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The emerging genomic landscape of endometrial cancer.

Cancers that arise in the body (corpus) of the uterus represent the eighth leading cause of cancer-related death among American women, accounting for an estimated 8190 deaths in 2013 (1). Worldwide, uterine corpus cancers caused approximately 74 000 deaths in 2008 (2). The majority of uterine corpus cancers are endometrial carcinomas, with the remaining cases (3%-5%) being sarcomas (stromal sarcomas, leiomyosarcomas, undifferentiated sarcomas, adenosarcomas) (3). Endometrial carcinomas can be further classified by histology as endometrioid adenocarcinoma, serous adenocarcinoma, clear cell adenocarcinoma, mixed cell carcinoma, mucinous adenocarcinoma, metaplastic carcinoma (carcinosarcoma), squamous cell carcinoma, transitional cell carcinoma, small cell carcinoma, undifferentiated carcinoma, and others (4). The classification of endometrial carcinomas by histologic subtype, clinical stage, and grade is important in assessing prognosis and in deciding the most appropriate treatment regimen [reviewed in (5)].

In the US, the survival rates for uterine corpus cancer show substantial racial disparity, with 5-year relative survival rates of only 57%-63% for African American women, compared with 84%-88% for white women (1). This difference in survival is explained at least in part by differences in socioeconomic status, access to healthcare, and the fact that compared with white women, African American women are more likely to be diagnosed with aggressive histologic subtypes, including serous carcinomas, clear cell carcinomas, and sarcomas [reviewed in (6)].

The majority of endometrial carcinomas arise sporadically via acquired somatic alterations. A large population-based, case control, genome-wide association study has recently identified a locus (rs1202524) on 1q42.2--in the vicinity of the CAPN9 [2] (calpain 9) gene--that maybe associated with an increased risk of endometrial cancer (7).

A small fraction of endometrial cancers are associated with an autosomal dominant inherited genetic susceptibility in the context of Lynch syndrome (hereditary nonpolyposis colorectal cancer) and Cowden syndrome (8-10). Lynch syndrome is attributed to germline mutations in mismatch-repair genes--MLH1 (mutL homolog 1), MSH2 (mutS homolog 2), MSH6 (mutS homolog 6), PMS2 [PMS2 postmeiotic segregation increased 2 (S. cerevisiae)]--as well as germline deletions of EPCAM (epithelial cell adhesion molecule) that produce transcriptional read-through leading to hypermethylation of the MSH2 promoter, which is located adjacent to EPCAM on chromosome 2p21. In contrast, Cowden syndrome is linked to germline mutations in the PTEN [3] tumor suppressor gene. A single-institution study found that the relative frequency of endometrioid and nonendometrioid carcinomas in endometrial cancer patients with Lynch syndrome was similar to their relative frequency in the general population (11). Recently, whole-genome sequencing of constitutional DNA from individuals diagnosed with multiple colorectal adenomas by age 60 years revealed that a germline mutation (Ser478Asn) in the POLD1 [polymerase (DNA directed), delta 1, catalytic subunit] gene, which encodes the catalytic subunit of polymerase [delta] that promotes lagging-strand synthesis during DNA replication, is linked to an inherited predisposition to both colorectal cancer and endometrial cancer (12). Several studies have suggested that serous endometrial carcinoma may be a component tumor of hereditary breast ovarian cancer syndrome [reviewed in (13)]. Strong epidemiologic evidence has shown that the increased incidence of serous endometrial carcinoma in carriers of BRCA1 (breast cancer 1, early onset) or BRCA2 (breast cancer 2, early onset) mutations is associated with prior tamoxifen treatment, rather than with an underlying genetic susceptibility (14). In this regard, it will be important to also ascertain whether tamoxifen use accounts for any of the documented increased risk for endometrial cancer associated with Cowden syndrome, which also includes breast cancer as a clinical manifestation.

A detailed discussion of the germline genomic alterations that confer susceptibility to endometrial cancer is the subject of another article in this special issue. In the present article, we review both the traditional histologic classification of endometrioid and serous endometrial carcinomas and the molecular classification of these tumors, which has emerged from a new appreciation of their somatic genomic landscapes (15-20).

Histologic Classification of Endometrial Carcinomas

ENDOMETRIOID ENDOMETRIAL CARCINOMA

Endometrioid endometrial carcinomas represent approximately 87%-90% of all diagnosed endometrial carcinomas (21). They are frequently estrogen-dependent tumors associated with epidemiologic risk factors that lead to unopposed estrogen exposure, including obesity, nulliparity, early age at menarche, and late age at menopause (22, 23). They maybe preceded by hyperplasia, atypical hyperplasia, and endometrial intraepithelial neoplasia, which is a premalignant outgrowth from benign endometrial hyperplasia [reviewed in (24)]. Most endometrioid tumors are diagnosed at an early clinical stage and are associated with an overall favorable prognosis (25). Treatment strategies for endometrioid endometrial carcinoma are guided not only by stage but also by tumor grade and depth of myometrial invasion, because a high tumor grade (grade 3) and/or infiltration of >50% of the myometrium are predictors of an increased risk for tumor recurrence [reviewed in (5)]. The treatment for patients with advanced-stage or recurrent disease is highly variable (26). The prognosis for advanced-stage disease is relatively poor, with one study noting 5-year overall-survival rates of 36%-56% for stage III disease and 21%-22% for stage IV disease (25). Although a number of molecularly targeted therapeutics are in clinical trials for endometrial carcinoma [reviewed in (5, 21)], there are currently no targeted therapies approved by the US Food and Drug Administration for this tumor type.

Over the past 2 decades in the era preceding next-generation sequencing, much effort was devoted to understanding the genetic etiology of endometrioid endometrial carcinomas [reviewed in (24)]. Most endometrioid endometrial carcinomas tend to be chromosomally stable, with diploid or near-diploid genomes (27). At the molecular level, these carcinomas are characterized by high-frequency genetic alterations in the PIK3CA, PIK3R1, and PTEN genes that produce inappropriate activation of the PI3K (phosphoinositide 3-kinase) [4] pathway (28-32). ARID1A, which encodes the BAF250A tumor suppressor, is somatically mutated in 40% of low-grade endometrioid endometrial carcinomas [reviewed in (24)]. Loss of BAF250A protein is likewise frequent and has been detected in 19% to 34% of endometrioid endometrial carcinomas overall, 26% to 29% of low-grade endometrioid endometrial carcinomas, 39% of high-grade endometrioid endometrial carcinomas, and 16% of endometrial hyperplasias with atypia suggesting that this phenomenon is an initiating event in endometrioid endometrial tumorigenesis [(33-35); reviewed in (24)]. Other signal transduction pathways that are frequently disrupted in endometrioid endometrial carcinomas include the RAS-RAF-MEK-ERK pathway, which is disrupted by somatic mutations in KRAS (approximately 18% of cases) or by hypermethylation of the RASSF1 [Ras association (RalGDS/AF-6) domain family member 1; alias, RASSF1A] promoter (62%-74% of cases) [(36); reviewed in (24)]. Somatic mutations in the FGFR2 receptor tyrosine kinase occur in approximately 12% of endometrioid endometrial carcinomas (36, 37). FGFR2 mutations and KRAS mutations are mutually exclusive (36). Although mutual exclusivity implies functional redundancy, the clinical correlates of KRAS and FGFR2 mutations are different, indicating possible differences in their biological effects (36). Endometrioid endometrial carcinomas often show disruption of the canonical WNT signaling pathway owing to somatic mutation of the CTNNB1 gene (2%-45% of cases) and stabilization of [beta]-catenin (36, 38, 39). Recent findings that CTNNB1 and KRAS mutations are mutually exclusive in endometrioid endometrial carcinomas have led to the proposal that functional cross talk between the RAS-RAF-MEK-ERK and WNT/TCF signaling pathways may occur in this cell type or that functional redundancy exists in the biological consequences of altered RAS-RAF-MEKERK and WNT/TCF signaling (36). In addition, endometrioid tumors often exhibit microsatellite instability (MSI), with an incidence of 34% MSI positivity noted in a recent large single-institution study of 466 cases (36) and 40% MSI positivity noted among endometrioid endometrial carcinomas selected for analysis by The Cancer Genome Atlas (TCGA) (15). The MSI phenotype in sporadic endometrial carcinomas has been attributed to defective mismatch repair, primarily due to hypermethylation of the MLH1 promoter, as well as to low-frequency somatic mutations in MSH6 and loss of MSH2 expression (40-42).

SEROUS ENDOMETRIAL CARCINOMA

Serous endometrial carcinomas, high-grade tumors that are often metastatic at presentation, have an associated 5-year relative survival rate of only 44.7%, compared with 91.2% for endometrioid endometrial carcinoma (43). Although they are rare at diagnosis, serous carcinomas are clinically aggressive and contribute substantially to the mortality from endometrial cancer. In one study, serous tumors constituted only 10% of endometrial cancer diagnoses but accounted for 39% of the deaths (44). Recent epidemiologic evidence suggests that, similar to endometrioid endometrial carcinoma, an increased body mass index may be a risk factor for serous endometrial carcinoma (23). Serous endometrial carcinomas may be preceded by precancerous cells with a so-called p53 signature, by endometrial glandular dysplasia, or by endometrial intraepithelial carcinoma [reviewed in (45)]. Treatment approaches for serous endometrial carcinoma are variable but generally include surgical staging and cytoreduction, followed by adjuvant chemotherapy and/or radiotherapy [reviewed in (46, 47)].

Although the genomic landscape of serous endometrial carcinoma has recently been deciphered (1518 ), prior molecular studies of individual genes and pathways have established that serous endometrial carcinomas are characterized by a high frequency (up to 90% of cases) of somatic mutations in TP53 and/or p53 stabilization (48, 49). TP53/p53 abnormalities are believed to be initiating events in the development of serous endometrial cancer on the basis of their occurrence in premalignant cells, in endometrial glandular dysplasia, and in endometrial intraepithelial carcinoma [reviewed in (24)]. Consistent with the idea that p53 dysregulation is an initiating event in serous endometrial tumorigenesis, mice with conditional deletion of TP53 in the genitourinary tract develop non-endometrioid endometrial carcinomas, including serous carcinomas (50). In addition to p53 alterations, human serous endometrial carcinomas also harbor frequent somatic mutations in the PPP2R1A gene (which encodes a subunit of the PP2A phosphatase) and in the PIK3CA, PIK3R1, and PTEN genes within the PI3K pathway [reviewed in (24)]. Increased amounts of the cell cycle proteins cyclin E and p16, amplification and overexpression of the ERBB2 [v-erb-b2 avian erythroblastic leukemia viral oncogene homolog 2] gene (which encodes the ERBB2 receptor tyrosine kinase), loss of BAF250A production, and altered amounts of the cell adhesion proteins claudin-3, claudin-4, L1CAM (L1 cell adhesion molecule), EpCAM (epithelial cell adhesion molecule), and E-cadherin have also been documented [reviewed in (24)].

HIGH-GRADE ENDOMETRIAL CARCINOMA

A substantial proportion of high-grade endometrial carcinomas can be difficult to classify reproducibly according to histologic subtype [reviewed in (51)]. For example, one study noted discordant subtype classification in approximately one-third of high-grade endometrial tumors (52). The difficulty in unambiguously classifying some high-grade endometrial carcinomas is problematic, because different histologic subtypes have different clinical behaviors and different treatment considerations [reviewed in (53)]. Immunochemical phenotyping for markers such as p53, estrogen receptor, progesterone receptor, PTEN, IMP3 (insulin-like growth factor 2 mRNA-binding protein 3), and p16 may serve as informative adjuncts to traditional histopathology for the classification of high-grade endometrial tumors, because unambiguously assigned histologic subtypes tend to show characteristic differences in the expression patterns of genes encoding these markers (54-56). In a combined analysis of immunohistochemical staining of grade 3 endometrioid endometrial carcinomas for MLH1, MSH2, p16, cyclin D1, ERBB2, WT1, and p53,37% of cases had molecular profiles that resembled endometrioid carcinomas, and the other 63% of cases resembled serous carcinomas at the molecular level (57). In the future, mutational profiles may also be useful adjuncts to histopathologic classification. For example, significant differences have been noted in the frequencies of mutations among the ARID1A, PTEN, PIK3CA, PPP2R1A (protein phosphatase 2, regulatory subunit A, alpha), TP53, and CTNNB1 genes in low-grade endometrioid endometrial carcinoma, high-grade endometrioid endometrial carcinoma, serous endometrial carcinoma, and endometrial carcinosarcomas, and the pattern of mutations in this 6-gene set has facilitated the histologic reclassification of some endometrial tumors (58). As we discuss later in this review, an integrated genomic analysis of endometrioid and serous endometrial carcinomas by TCGA has revealed that 19.6% of histologically classified high-grade (grade 3) endometrioid endometrial carcinomas in that study have genomic profiles that resemble those of serous carcinomas (15).

Molecular Classification of Endometrioid and Serous Endometrial Carcinomas

Although much progress has been made over the past several decades toward understanding the molecular etiology of endometrial carcinomas, the very recent application of next-generation sequencing to comprehensively search for somatic alterations in endometrial carcinomas has led to a rapid and substantial shift in our understanding of the molecular events underlying these tumors. Beginning in 2012, several studies, including one from our own group, reported the results of systematic searches for somatic mutations in serous and endometrioid endometrial carcinomas in the approximately 22 000 protein-encoding genes that constitute the exome (16-20). The first large-scale, fully integrated genomic analysis of endometrial carcinomas, which was reported in 2013 by TCGA (15), used whole-exome sequencing, whole-transcriptome sequencing, genome-wide copy number analysis, expression profiling, reverse-phase protein array, methylation profiling, and MSI assessment to interrogate 186 endometrioid, 42 serous, and 4 mixed-histology endometrial carcinomas in an integrated manner (15). A subset of TCGA tumors (n = 107) was also subjected to low-pass whole-genome sequencing to identify structural variants. Together, these studies have provided critical new insights into the molecular features of serous and endometrioid endometrial carcinomas, including the first observation (reported by TCGA)-based on an integrated analysis of somatic mutation rates, frequency of copy number alterations, and MSI status--that endometrial carcinomas can be broadly classified into 4 distinct molecular subgroups. The following sections provide an overview of the most salient features of the 4 molecular subgroups identified by TCGA. These subgroups are termed "POLE ultramutated," "hypermutated/microsatellite-unstable," "copy number low/microsatellite-stable" "copy number high (serous-like)."

POLE ULTRAMUTATED SUBGROUP

As the name suggests, ultramutated tumors have an extraordinarily high mutation rate (232 X [10.sub.-6] mutations/Mb; 867-9714 mutations/tumor) and an increased incidence of C>A transversions (15). Overall, 6.4% of low-grade endometrioid endometrial carcinomas and 17.4% of high-grade endometrioid endometrial carcinomas--but none of the mixed histology or serous tumors in the TCGA study--were ultramutated. The ultramutated phenotype is attributed to somatic mutations in the exonuclease domain of POLE, which encodes the catalytic and proofreading subunit of the polymerase e holoenzyme that catalyzes leading-strand synthesis during DNA replication and regulates cell cycle progression, chromatin remodeling, and DNA repair (59). In an earlier study, Church et al. described somatic mutations in the exonuclease domain of POLE in 7% of endometrioid, 25% of serous, and 33% of mixed-histology endometrial carcinomas, although it is important to note that the total number of serous and mixed-histology tumors in that study was small (60). Church et al. also noted a significant increase in the incidence of POLE mutations with high tumor grade (4.7% grade 1 tumors vs. 1.7% grade 2 tumors vs. 22.2% grade 3 tumors; P = 0.001) (60).

TCGA uncovered 190 significantly mutated genes (defined in that study as having a false-discovery rate in the convolution test of [less than or equal to] 2%) among POLE ultramutated tumors. Significantly enriched pathways (P values <0.01) associated with this subgroup involve gluconeogenesis, glycolysis, clathrin-mediated endocytosis signaling, tRNA charging, tricarboxylic acid cycle II (eukaryotic), and actin cytoskeleton signaling. Although the number of ultramutated endometrial carcinomas that have been described thus far is small, it is noteworthy that the progression-free survival ofpatients in the ultramutated subgroup are more favorable than for other molecular subgroups [hypermutated/microsatellite-unstable, copy number low/microsatellite-stable, or copy number high (serous-like)] (15).

HYPERMUTATED/MICROSATELLITE-UNSTABLE SUBGROUP

The so-called hypermutated/microsatellite-unstable endometrial cancer subgroup is composed of microsatellite-unstable tumors that have low-level somatic copy number alterations (15). Consistent with their MSI phenotype, the hypermutated/microsatellite-unstable subgroup also displays frequent MLH1 promoter methylation and reduced MLH1 gene expression. Hypermutated/microsatellite-unstable tumors are also associated with a heavily methylated subgroup suggestive of a CpG methylator phenotype. In the TCGA tumor cohort, 28.6% of low-grade endometrioid endometrial carcinomas and 54.3% of high-grade endometrioid endometrial carcinomas were within the hypermutated/ microsatellite-unstable subgroup. This observation is consistent with earlier reports that MSI positivity occurs at a significantly higher frequency in high-grade endometrioid endometrial carcinomas than in low-grade endometrioid endometrial carcinomas (61-63). None of the mixed-histology or serous endometrial carcinomas in the TCGA cohort were within the hypermutated/microsatellite-unstable subgroup (15). The absence of serous endometrial carcinomas from the hypermutated/microsatellite unstable subgroup is in accord with the infrequent (0%-4%) occurrence of MSI documented in serous tumors by TCGA and in earlier analyses of other large cohorts of serous endometrial carcinoma (15, 18, 58, 64).

Twenty-one significantly mutated genes (candidate pathogenic driver genes) have been identified in the hypermutated/microsatellite-unstable subgroup (Table 1), including 11 genes (ARID5B, CSDE1, CTCF, GIGYF2, HIST1H2BD, LIMCH1, MIR1277, NKAP, RBMX, TNFAIP6, ZFHX3) that were not previously known to be significantly mutated in endometrial carcinoma. Most of the remaining significantly mutated genes (PTEN, PIK3CA, PIK3R1, ARID1A, RPL22, KRAS, CTNNB1, ATR, FGFR2, CCND1) have well-documented roles in the endometrioid subtype, as discussed earlier in this review and elsewhere (24, 65). The role ofRPL22 in endometrioid endometrial carcinomas is emerging. Somatic mutations at a polynucleotide tract within RPL22, which lead to protein truncation, were previously demonstrated to occur in 52% of MSI-high endometrioid endometrial carcinomas and to correlate with a later age at diagnosis (67 vs. 63 years, P = 0.0005) (66). Although the functional effect of RPL22 mutations in endometrial cancer remains to be determined, it is noteworthy that RPL22 has been suggested to be a haploinsufficient tumor suppressor gene, based on observations that 10% of primary T-cell acute lymphoblastic leukemias exhibit monoallelic deletion of RPL22 and that haploinsufficiency for RPL22 accelerates tumorigenesis in a mouse model of T-cell lymphoma (67).

In addition to significantly mutated genes, a number of significantly enriched pathways have been recognized in the hypermutated/microsatellite-unstable subgroup, including the threonine degradation II, glycine degradation, and anandamide degradation pathways. The RTK (receptor tyrosine kinase)/RAS/[beta]-catenin pathway is altered in 69.5% of hypermutated/ microsatellite-unstable tumors and the PIK3CAPIK3R1-PTEN axis is genomically altered in 95.5% of cases. As noted previously, targeted therapies directed against the PI3K pathway are currently being evaluated in clinical trials for the treatment of endometrial cancer [reviewed in (21)]. KRAS alterations, which may confer resistance to PI3K pathway inhibitors [reviewed in (68)], were observed in 35% of hypermutated/ microsatellite-unstable endometrial tumors (15). An earlier, large study of endometrioid endometrial carcinomas demonstrated that somatic mutations in KRAS and FGFR2 were significantly more frequent among MSI-positive than MSI-negative endometrioid tumors, whereas CTNNB1 mutations were significantly more frequent among MSI-negative tumors (36).

Historically, there has been considerable interstudy variability regarding whether MSI status is associated with the clinical outcome of endometrial cancer. Factors proposed to account for this variability include differences in the numbers of patients between studies, as well as differences in the histopathologic composition of study cohorts (61). A recent large single-institution study of endometrioid endometrial cancer cases observed no significant correlation between MSI status and either overall survival or disease-free survival (61). Moreover, a recently published metaanalysis of 23 studies, including the aforementioned study (61), also observed no significant correlation between MSI and clinical outcome for endometrial cancer (69).

COPY NUMBER-LOW/MICROSATELLITE-STABLE SUBGROUP

The copy number-low/microsatellite-stable subgroup described by TCGA included 60.0% of low-grade endometrioid carcinomas, 8.7% of high-grade endometrioid carcinomas, 2.3% of serous carcinomas, and 25% of mixed-histology carcinomas. Sixteen significantly mutated genes were discerned in this molecular subgroup (Table 1): 9 genes previously implicated in endometrial cancer (PTEN, PIK3CA, CTNNB1, ARID1A, PIK3R1, KRAS, FGFR2, CHD4, SPOP) by us and others [(17, 18); reviewed in (24)], and 7 genes (BCOR, CSMD3, CTCF, MECOM, METTL14, SGK1, SOX17) not previously recognized to have a role in endometrial tumorigenesis. Although significantly mutated genes are generally indicative of probable pathogenic driver genes, the designation of CSMD3 as a significantly mutated gene in endometrial cancer likely reflects the inadequacy of statistical algorithms to account for the observations that late-replicating genes and low-expressed genes, such as CSMD3, exhibit higher background mutation rates than early-replicating genes or highly expressed genes (70). Therefore, the designation of CSMD3 as a significantly mutated gene in endometrial cancer likely reflects an increased background mutation rate rather than the accumulation of pathogenic driver mutations (70).

Almost all (92%) of the tumors in this subgroup have somatically altered the PI3K pathway. KRAS is altered in 16% of cases, considerably lower than the frequency of KRAS mutation in hypermutated/ microsatellite-unstable endometrial carcinomas, which is in accord with earlier observations that KRAS mutations are significantly more common in microsatellite-unstable endometrioid tumors than in microsatellite-stable endometrioid tumors (36). The RTK/RAS/[beta]-catenin pathway is also altered at high frequency (83%) among copy number-low/microsatellite-stable tumors, and within this pathway somatic mutations in CTNNB1 are particularly prevalent (52%). Mutations in SOX17, which regulate [beta]-catenin, are observed exclusively in this subgroup.

COPY NUMBER-HIGH (SEROUS-LIKE) SUBGROUP

In the TCGA study, 5.0% of low-grade endometrioid carcinomas, 19.6% of high-grade endometrioid carcinomas, 97.7% of serous carcinomas, and 75% of mixed-histology carcinomas were in the copy number-high tumor subgroup. That almost all serous endometrial carcinomas in the TCGA study are deemed copy number high is consistent with previous reports that serous endometrial carcinomas are often aneuploid and chromosomally unstable (16, 17, 71, 72).

The TCGA study described 8 significantly mutated genes, including CSMD3, among the 60 copy number-high (serous-like) tumors (Table 1). The inclusion of CSMD3, as discussed earlier in this review, probably reflects a statistical artifact rather than CSMD3 being a bona fide driver gene. The other significantly mutated genes in the serous-like subgroup were TP53, PIK3CA, PTEN, PIK3R1, and PPP2R1A, which have well-established roles in serous endometrial tumors [reviewed in (24) ], and FBXW7 and CHD4, which we and others previously identified as significantly mutated genes in serous endometrial carcinomas (16-18). With the exception of CHD4, each of the aforementioned genes is a bona fide cancer gene. As has previously been noted for TP53, the presence of somatic mutations within FBXW7, PIK3CA, and PPP2R1A in serous intraepithelial carcinoma and concurrent serous endometrial carcinomas implicates mutation of these genes as early events in the development of serous endometrial cancer (16). The functional consequences of mutations in CHD4, which encodes the catalytic subunit of the NuRD chromatin-remodeling complex, remain to be elucidated; however, the designation of CHD4 as a significantly mutated gene in serous and serous-like tumors (15, 17, 18) and the presence of mutation hot spots within this gene strongly suggest it is likely to be a causal driver gene.

Other genes that have emerged as significantly mutated genes in whole-exome sequencing studies of serous endometrial carcinomas are SPOP, a putative tumor suppressor gene; CDKN1A [cyclin-dependent kinase inhibitor 1A (p21, Cip1)], a bona fide cancer gene; TAF1; HCFC1R1 [host cell factor C1 regulator 1 (XPO1 dependent)]; CTDSPL [CTD (carboxy-terminal domain, RNA polymerase II, polypeptide A) small phosphatase-like]; YIPF3 (Yip1 domain family, member 3); and FAM132A (family with sequence similarity 132, member A) (17, 18). In terms of biological processes, genes that are involved in chromatin remodeling and ubiquitin-mediated protein degradation are frequently mutated in serous endometrial tumors (18). That is not to say that chromatin-remodeling genes and genes of the ubiquitin ligase complex are not also perturbed in the endometrioid subtype; indeed, a number of chromatin-remodeling genes, such as ARID1A, ARID5B, CTCF, and CHD4, are also causal or candidate driver genes in molecular subgroups dominated by endometrioid endometrial tumors (Table 1).

Statistical methods have been used to define a number of genomic regions of significant copy number alteration in serous-like tumors, including regions of focal amplification involving the MYC (v-myc avian myelocytomatosis viral oncogene homolog) oncogene, the ERBB2 (HER2) receptor tyrosine kinase gene, and CCNE1 (cyclin E1), which are each focally amplified in 23%-25% of cases (15). The mutual exclusivity in serous tumors of CCNE1 amplification and somatic alterations affecting FBXW7, which normally mediates the ubiquitin-mediated degradation of cyclin E, suggests that these genetic events are functionally redundant (16). The observation of frequent MYC, ERBB2, and CCNE1 gene amplification in serous-like endometrial carcinomas is consistent with prior observations of serous endometrial carcinomas [(16, 17); reviewed in (24)]. Numerous additional genes of interest, including PIK3CA, FBXW7, CHD4, and MBD3 (methyl-CpG binding domain protein 3), are located within larger regions of copy number alteration in serous and serous-like endometrial carcinomas (15-17).

Copy number-high (serous-like) endometrial tumors have a DNA methylation pattern similar to that of the normal endometrium. A large proportion (85%) of tumors in the copy number-high (serous-like) subgroup are also within a so-called mitotic subgroup, defined by altered mRNA production for genes involved in cell cycle regulation (15). RNA sequencing has also revealed transcriptional differences that form significantly enriched pathways in the copy number-high (serous-like) subgroup, including G1/S checkpoint regulation, growth hormone signaling, Her-2 signaling in breast cancer, endothelin-1 signaling, cyclins and cell cycle regulation, and molecular mechanisms of cancer (15). Furthermore, in the serous-like molecular subgroup, increased p53 protein levels and decreased phospho-AKT protein levels have been noted by reverse-phase protein array analysis (15).

The simultaneous assessment of the entire complement of protein-encoding genes by TCGA revealed that most of the ERBB2-amplified serous-like tumors also were PIK3CA mutated (P = 0.038). As noted (15), the co-occurrence of ERBB2 amplification and PIK3CA mutation in serous-like tumors may be clinically relevant, because in ERBB2-overexpressing breast cancer cell lines, activating mutations in PIK3CA are associated with decreased sensitivity to trastuzumab and lapatinib, therapeutic agents that target ERBB2 (73, 74). This observation illustrates the importance of evaluating the larger genomic context of druggable targets when, for example, considering the design and interpretation of clinical trials assessing targeted therapies. A small number of studies have assessed the clinical efficacy of trastuzumab for the treatment of ERBB2-positive advanced or recurrent endometrial cancer [reviewed in (75)], and additional clinical trials of trastuzumab or lapatinib for treating endometrial cancer are ongoing or planned (NCT01367002, NCT01454479). As these and other trials of targeted therapies directed against ERBB2 in endometrial cancer proceed, it maybe useful to assess whether PIK3CA mutation status has an effect on clinical response. The PIK3CA-PIK3R1-PTEN axis itself is altered in 73% of copy number-high (serous-like) tumors, whereas KRAS is mutated or amplified in 8% of serous-like tumors (15). The clinical efficacy of therapeutic agents targeting the PI3K/AKT/mTOR pathway in the treatment of endometrial cancer has recently been reviewed elsewhere (68).

One of the most interesting findings from the genomic analysis of endometrial tumors is that approximately one-fifth of tumors classified as grade 3 endometrioid endometrial carcinomas are "serous-like" at the molecular level. As noted in the TCGA study, the distinction between the histologic and molecular classification of these cases has important clinical implications--suggesting that patients who have grade 3 endometrioid endometrial carcinomas with a serous-like genomic profile might be treated more appropriately with regimens that are used for serous carcinoma. As is discussed earlier in this review, a subset of high-grade endometrial tumors is difficult to classify accurately by subtype at the histologic level. The newfound realization that serous and endometrioid endometrial tumors can be molecularly classified into 4 distinct subgroupings may provide future opportunities to devise a panel of biomarkers, or indeed use integrated genomic profiling, to augment the traditional histopathologic classification of endometrial carcinomas. In this regard, it is notable that 48 significantly mutated genes are altered at different frequencies across the 4 molecular subgroups of endometrial carcinoma reported by TCGA (Table 2). How the genomic profiles of endometrioid and serous endometrial carcinomas relate to the genomic profiles of other endometrial carcinoma subtypes remains to be determined.

Conclusions and Future Perspectives

In the past year, the pace of mutation discovery in endometrial cancer has been unprecedented. To date, the exomes of 96 serous and 233 endometrioid endometrial carcinomas have been deciphered (15-20). The integrated genomic analysis of these 2 subtypes of endometrial cancer by TCGA (15), as well as studies from individual laboratories (16-20), has provided unprecedented insights into the genomic, epigenomic, transcriptomic, and proteomic alterations that are present in serous and endometrioid endometrial tumors. Together, these studies have given the endometrial cancer community the most comprehensive view of the genomic landscape of this disease thus far. It is likely that our view of this landscape--and the genetic and biological context of the alterations that shape it--will continue to be refined and defined by the functional annotation of candidate cancer genes that have emerged from these studies and by the sequencing of additional endometrial tumors, including rare histologic subtypes. Prospective studies assessing the potential clinical utility of these findings will undoubtedly follow. One can envision that the molecular classification of endometrial tumors might assist in guiding a determination of prognosis and treatment decisions, in the discovery of new druggable targets and pathways, and in implementing molecular diagnostics to detect endometrial cancers at an earlier stage in their clinical course, when the prognosis is more favorable. In the latter case, it is noteworthy that the genomic analysis of cells collected during Papanicolaou tests holds promise for the early detection of endometrial carcinomas (19). In future studies, it will also be important to decipher the genomic landscape of metastatic disease and the precancerous lesions that precede endometrial carcinomas, as well as annotating and functionalizing somatic aberrations in the noncoding regions of the genome in endometrial carcinomas.

Author Contributions: All authors confirmed they have contributed to the intellectual content of this paper and have met the following 3 requirements: (a) significant contributions to the conception and design, acquisition of data, oranalysis and interpretation of data; (b) drafting or revising the article for intellectual content; and (c) final approval of the published article.

Authors' Disclosures or Potential Conflicts ofInterest: Upon manuscript submission, all authors completed the author disclosure form. Disclosures and/or potential conflicts ofinterest:

Employment or Leadership: None declared.

Consultant or Advisory Role: None declared.

Stock Ownership: None declared.

Honoraria: None declared.

Research Funding: D.W. Bell, Intramural Program of the National Institutes ofHealth.

Expert Testimony: None declared.

Patents: D.W. Bell, United States patent US 8,465,916 B2.

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Matthieu Le Gallo [1] and Daphne W. Bell [1] *

[1] Cancer Genetics Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD.

* Address correspondence to this author at: National Human Genome Research Institute, Cancer Genetics Branch, 50 South Dr., MSC-8000, Bethesda, MD 20892. Fax 301-594-1360; e-mail belldaph@mail.nih.gov.

Received July 15, 2013; accepted October 10, 2013.

Previously published online at DOI: 10.1373/clinchem.2013.205740

[2] Human genes: CAPN9, calpain 9; MLH1, mutL homolog 1; MSH2, mutS homolog 2; MSH6, mutS homolog 6; PMS2, PMS2 postmeiotic segregation increased 2 (S. cerevisiae); EPCAM, epithelial cell adhesion molecule; PTEN, phosphatase and tensin homolog; POLD1, polymerase (DNA directed), delta 1, catalytic subunit; BRCA1, breast cancer 1, early onset; BRCA2, breast cancer 2, early onset; PIK3CA, phosphatidylinositol-4,5-bisphosphate 3-kinase, catalytic subunit alpha; PIK3R1, phosphoinositide-3-kinase, regulatory subunit 1 (alpha); ARID1A, AT rich interactive domain 1A (SWI-like); KRAS, Kirsten rat sarcoma viral oncogene homolog; RASSF1, Ras association (RalGDS/AF-6) domain family member 1; alias, RASSF1A; FGFR2, fibroblast growth factor receptor 2; CTNNB1, catenin (cadherin-associated protein), beta 1, 88kDa; TP53, tumor protein p53; ERBB2, v-erb-b2 avian erythroblastic leukemia viral oncogene homolog 2; PPP2R1A, protein phosphatase 2, regulatory subunit A, alpha; POLE, polymerase (DNA directed), epsilon, catalytic subunit; ARID5B, AT rich interactive domain 5B (MRF1-like); CSDE1, cold shock domain containing E1, RNA-binding; CTCF, CCCTC-binding factor (zinc finger protein); GIGYF2, GRB10 interacting GYF protein 2; HIST1H2BD, histone cluster 1, H2bd; LIMCH1, LIM and calponin homology domains 1; MIR1277, microRNA 1277; NKAP, NFKB activating protein; RBMX, RNA binding motif protein, X-linked; TNFAIP6, tumor necrosis factor, alpha-induced protein 6; ZFHX3, zinc finger homeobox 3; RPL22, ribosomal protein L22; ATR, ataxia telangiectasia and Rad3 related; CCND1, cyclin D1; CHD4, chromodomain helicase DNA binding protein 4; SPOP, speckle-type POZ protein; BCOR, BCL6corepressor; CSMD3, CUB and Sushi multiple domains 3; MECOM, MDS1 and EVI1 complex locus; METTL14, methyltransferase like 14; SGK1, serum/glucocorticoid regulated kinase 1; SOX17, SRY (sex determining region Y)-box 17; FBXW7, F-box and WD repeat domain containing 7, E3 ubiquitin protein ligase; CDKN1A, cyclin-dependent kinase inhibitor 1A (p21, Cip1); TAF1, TAF1 RNA polymerase II, TATA box binding protein (TBP)associated factor, 250kDa; HCFC1R1, host cell factor C1 regulator 1 (XPO1 dependent); CTDSPL, CTD (carboxy-terminal domain, RNA polymerase II, polypeptide A) small phosphatase-like; YIPF3, Yip1 domain family, member 3; FAM132A, family with sequence similarity 132, member A; CCNE1, cyclin E1; MYC, v-myc avian myelocytomatosis viral oncogene homolog; MBD3, methylCpG binding domain protein 3; MKI67, antigen identified by monoclonal antibody Ki-67; FAT3, FAT atypical cadherin 3; SPTA1, spectrin, alpha, erythrocytic 1 (elliptocytosis 2); FAM135B, family with sequence similarity 135, member B; KMT2B, lysine (K)-specific methyltransferase 2B (also known as: MLL4, myeloid/lymphoid or mixed-lineage leukemia protein 4); USH2A, Usher syndrome 2A (autosomal recessive, mild); RRN3P2, RNA polymerase I transcription factor homolog (S cerevisiae) pseudogene 2; CDH19, cadherin 19, type 2; USP9X, ubiquitin specific peptidase 9, X-linked; COL11A1, collagen, type XI, alpha 1; ZNF770, zinc finger protein 770; SLC9C2, solute carrier family 9, member C2 (putative); PNN, pinin, desmosome associated protein; INPP4A, inositol polyphosphate-4-phosphatase, type I, 107kDa; AMY2B, amylase, alpha 2B (pancreatic); SIN3A, SIN3 transcription regulator family member A; HOXA7, homeobox A7; HPD, 4-hydroxyphenylpyruvate dioxygenase; NFE2L2, nuclear factor, erythroid 2-like 2; ESR1, estrogen receptor 1.

[3] See Tables 1 and 2 for the gene names for symbols not expanded on their first appearance in the text.

[4] Nonstandard abbreviations: PI3K, phosphoinositide 3-kinase; MSI, microsatellite instability; TCGA, The Cancer Genome Atlas; L1CAM, L1 cell adhesion molecule; EpCAM, epithelial cell adhesion molecule; IMP3, insulin-like growth factor 2 mRNA-binding protein 3; RTK, receptor tyrosine kinase.
Table 1. Significantly mutated genes (SMGs) in 3 molecular
subgroups of endometrial cancer. (a)

Molecular           No. of   Gene
subgroup             SMGs    symbol

Hypermutated/         21     PTEN
  microsatellite-            PIK3CA
  unstable                   PIK3R1
                             ARID1A
                             RPL22
                             KRAS
                             ZFHX3
                             ARID5B
                             CTCF
                             CTNNB1
                             ATR
                             GIGYF2
                             CSDE1
                             FGFR2
                             CCND1
                             LIMCH1
                             RBMX
                             NKAP
                             HIST1H2BD
                             TNFAIP6
                             MIR1277
Copy number low/      16     PTEN
  microsatellite-            PIK3CA
  stable                     CTNNB1
                             ARID1A
                             PIK3R1
                             CTCF
                             KRAS
                             FGFR2
                             CHD4
                             SPOP
                             CSMD3 (b)
                             SOX17
                             SGK1
                             BCOR
                             MECOM
                             METTL14
Copy number high      8      TP53
  (serous-like)              PIK3CA
                             FBXW7
                             PPP2R1A
                             PIK3R1
                             CHD4
                             PTEN
                             CSMD3 (b)

Molecular           Gene name                        Somatic-mutation
subgroup                                                frequency

Hypermutated/       Phosphatase and tensin homolog        87.7%
  microsatellite-   Phosphatidylinositol-4,5-             53.8%
  unstable            bisphosphate 3-kinase,
                      catalytic subunit alpha
                    Phosphoinositide-3-kinase,            41.5%
                      regulatory subunit 1 (alpha)
                    AT rich interactive domain 1A         36.9%
                      (SWI-like)
                    Ribosomal protein L22                 36.9%
                    Kirsten rat sarcoma viral             35.4%
                      oncogene homolog
                    Zinc finger homeobox 3                30.8%
                    AT rich interactive domain            23.1%
                      5B (MRF1-like)
                    CCCTC-binding factor                  23.1%
                      (zinc finger protein)
                    Catenin (cadherin-associated          20.0%
                      protein), beta 1, 88kDa
                    Ataxia telangiectasia and Rad3        18.5%
                      related
                    GRB10 interacting GYF                 16.9%
                      protein 2
                    Cold shock domain containing          15.4%
                      E1, RNA-binding
                    Fibroblast growth factor              13.8%
                      receptor 2
                    Cyclin D1                             12.3%
                    LIM and calponin homology             12.3%
                      domains 1
                    RNA binding motif protein,            12.3%
                      X-linked
                    NFKB activating protein               10.8%
                    Histone cluster 1, H2bd                7.7%
                    Tumor necrosis factor,                 7.7%
                      alpha-induced protein 6
                    microRNA 1277                          6.2%
Copy number low/    Phosphatase and tensin homolog        76.7%
  microsatellite-   Phosphatidylinositol-4,5-             53.3%
  stable              bisphosphate 3-kinase,
                      catalytic subunit alpha
                    Catenin (cadherin-associated          52.2%
                      protein), beta 1, 88kDa
                    AT rich interactive domain            42.2%
                      1A (SWI-like)
                    Phosphoinositide-3-kinase,            33.3%
                      regulatory subunit 1 (alpha)
                    CCCTC-binding factor                  21.1%
                      (zinc finger protein)
                    Kirsten rat sarcoma viral             15.6%
                      oncogene homolog
                    Fibroblast growth factor              13.3%
                      receptor 2
                    Chromodomain helicase                 12.2%
                      DNA binding protein 4
                    Speckle-type POZ protein              10.0%
                    CUB and Sushi multiple                10.0%
                      domains 3
                    SRY (sex determining                   7.8%
                      region Y)-box 17
                    Serum/glucocorticoid regulated         6.7%
                      kinase 1
                    BCL6 corepressor                       6.7%
                    MDS1 and EVI1 complex locus            4.4%
                    Methyltransferase like 14              3.3%
Copy number high    Tumor protein p53                     91.7%
  (serous-like)     Phosphatidylinositol-4,5-             46.7%
                      bisphosphate 3-kinase,
                      catalytic subunit alpha
                    F-box and WD repeat domain            21.7%
                      containing 7, E3 ubiquitin
                      protein ligase
                    Protein phosphatase 2,                21.7%
                      regulatory subunit A, alpha
                    Phosphoinositide-3-kinase,            13.3%
                      regulatory subunit 1 (alpha)
                    Chromodomain helicase DNA             13.3%
                      binding protein 4
                    Phosphatase and tensin homolog        10.0%
                    CUB and Sushi multiple                10.0%
                      domains 3

(a) The Cancer Genome Atlas Research Network et al. (15).

(b) Probable false positive [Lawrence et al. (70)).

Table 2. Forty-eight SMGs mutated at different frequencies across
4 molecular subgroups of serous and endometrioid endometrial
cancers. (a)

Gene        Gene Name
Symbol

TP53        Tumor protein p53
PTEN        Phosphatase and tensin homolog
POLE        Polymerase (DNA directed), epsilon, catalytic subunit
MKI67       Antigen identified by monoclonal antibody Ki-67
FAT3        FAT tumor suppressor homolog 3 (Drosophila)
TAF1        TAF1 RNA polymerase II, TATA box binding protein
              (TBP)-associated factor, 250kDa
ZFHX3       Zinc finger homeobox 3
RPL22       Rlbosomal protein L22
SPTA1       Spectrin, alpha, erythrocytic 1 (elllptocytosls 2)
FAM135B     Family with seguence similarity 135, member B
CSMD3 (b)   CUB and Sushi multiple domains 3
GIGYF2      GRB10 Interacting GYF protein 2
CSDE1       Cold shock domain containing E1, RNA-binding
KMT2B (c)   Lysine (K)-speclflc methyltransferase 2B
ATR         Ataxia telangiectasia and Rad3 related
CTNNB1      Catenln (cadherln-assoclated protein), beta 1, 88kDa
USH2A       Usher syndrome 2A (autosomal recessive, mild)
LIMCH1      LIM and calponln homology domains 1
RRN3P2      RNA polymerase I transcription factor homolog
              (S. cerevisiae) pseudogene 2
FBXW7       F-box and WD repeat domain containing 7, E3 ubiquitin
              protein ligase
CDH19       Cadherln 19, type 2
USP9X       Ubiquitin specific peptidase 9, X-linked
C0L11A1     Collagen, type XI, alpha 1
BCOR        BCL6 corepressor
ARID1A      AT rich Interactive domain 1A (SWI-like)
ZNF770      Zinc finger protein 770
ARID5B      AT rich interactive domain 5B (MRF1 -like)
SLC9C2      Solute carrier family 9, member C2 (putative)
KRAS        v-Ki-ras2 Kirsten rat sarcoma viral oncogene homolog
PNN         Pinin, desmosome associated protein
INPP4A      Inositol polyphosphate-4-phosphatase, type I, 107kDa
CTCF        CCCTC-binding factor (zinc finger protein)
CHD4        Chromodomain helicase DNA binding protein 4
AMY2B       Amylase, alpha 2B (pancreatic)
RBMX        RNA binding motif protein, X-linked
PPP2R1A     Protein phosphatase 2, regulatory subunit A, alpha
SIN3A       SIN3 transcription regulator family member A
TNFAIP6     Tumor necrosis factor, alpha-induced protein 6
PIK3R1      Phosphoinositide-3-kinase, regulatory subunit 1 (alpha)
SGK1        Serum/glucocorticoid regulated kinase 1
H0XA7       Homeobox A7
METTL14     Methyltransferase like 14
HPD         4-hydroxyphenylpyruvate dioxygenase
MIR1277     MicroRNA 1277
CCND1       Cydin D1
MECOM       MDS1 and EVI1 complex locus
NFE2L2      Nuclear factor, erythroid 2-like 2
ESRI        Estrogen receptor 1

                           Mutation frequency

Gene            POLE         Hypermutated/        Copy number
Symbol      ultramutated    microsatellite     low/microsatellite
              (n = 17)     unstable (n = 65)    stable (n = 90)

TP53            35%               8%                   1%
PTEN            94%               88%                 77%
POLE            100%              8%                   3%
MKI67           94%               18%                  2%
FAT3            76%               31%                  1%
TAF1            82%               25%                  1%
ZFHX3           82%               31%                  2%
RPL22           29%               37%                  0%
SPTA1           76%               14%                  6%
FAM135B         76%               11%                  4%
CSMD3 (b)       94%               22%                 10%
GIGYF2          59%               20%                  0%
CSDE1           59%               15%                  1%
KMT2B (c)       65%               22%                  4%
ATR             65%               9%                   0%
CTNNB1          41%               20%                 52%
USH2A           76%               18%                  4%
LIMCH1          53%               12%                  0%
RRN3P2           6%               0%                   0%
FBXW7           82%               9%                   6%
CDH19           59%               5%                   1%
USP9X           59%               17%                  1%
C0L11A1         71%               9%                   2%
BCOR            65%               17%                  7%
ARID1A          76%               37%                 42%
ZNF770          41%               5%                   0%
ARID5B          47%               23%                  6%
SLC9C2          53%               5%                   2%
KRAS            53%               35%                 16%
PNN             35%               6%                   0%
INPP4A          29%               9%                   2%
CTCF            41%               23%                 21%
CHD4            65%               6%                  12%
AMY2B           29%               8%                   0%
RBMX            24%               12%                  0%
PPP2R1A         29%               9%                   1%
SIN3A           35%               14%                  4%
TNFAIP6         29%               2%                   1%
PIK3R1          65%               40%                 33%
SGK1            35%               3%                   6%
H0XA7           18%               6%                   0%
METTL14         24%               5%                   3%
HPD             12%               6%                   0%
MIR1277         12%               6%                   0%
CCND1           18%               12%                  4%
MECOM           24%               5%                   4%
NFE2L2          12%               11%                  3%
ESRI            24%               2%                   6%

                Mutation frequency

Gene            Copy          All 4
Symbol       number high    subgroups
            (serous-like)   (n = 232)
              (n = 60)

TP53             92%           29%
PTEN             10%           64%
POLE             2%            11%
MKI67            0%            13%
FAT3             0%            15%
TAF1             5%            15%
ZFHX3            7%            17%
RPL22            0%            13%
SPTA1            0%            12%
FAM135B          2%            11%
CSMD3 (b)        10%           19%
GIGYF2           7%            12%
CSDE1            0%            9%
KMT2B (c)        0%            13%
ATR              2%            8%
CTNNB1           3%            30%
USH2A            5%            14%
LIMCH1           0%            7%
RRN3P2           0%            0%
FBXW7            22%           16%
CDH19            5%            7%
USP9X            2%            10%
C0L11A1          8%            11%
BCOR             0%            12%
ARID1A           5%            34%
ZNF770           0%            4%
ARID5B           0%            12%
SLC9C2           3%            7%
KRAS             3%            21%
PNN              0%            4%
INPP4A           0%            6%
CTCF             0%            18%
CHD4             13%           15%
AMY2B            0%            4%
RBMX             0%            5%
PPP2R1A          22%           11%
SIN3A            0%            8%
TNFAIP6          0%            3%
PIK3R1           13%           32%
SGK1             2%            6%
H0XA7            0%            3%
METTL14          0%            4%
HPD              0%            3%
MIR1277          0%            3%
CCND1            0%            6%
MECOM            0%            5%
NFE2L2           0%            5%
ESRI             2%            5%

(a) The Cancer Genome Atlas Research Network et al. (15).
Mutation frequencies of protein-encoding genes were retrieved
via cBioPortal (http://www.cbioportal.org/public-portal/),
The mutation frequency of MIR1277 was retrieved via the TCGA
data portal (https://tcga-data.nci.nih.gov/tcga/),

(b) Probable false positive [Lawrence et al. (70)].

(c) HUGO-approved gene symbol and name. Also known
as MLL4 (myeloid/lymphoid or mixed-lineage leukemia protein 4).
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Author:Le Gallo, Matthieu; Bell, Daphne W.
Publication:Clinical Chemistry
Article Type:Report
Date:Jan 1, 2014
Words:9056
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