p53 mutation in adenocarcinoma arising in retrorectal cyst hamartoma (tailgut cyst): report of 2 cases--an immunohistochemistry/immunoperoxidase study.

Retrorectal cyst hamartoma (RCH), also commonly known as tailgut cyst, is a rare benign cystic lesion located in the retrorectal space and is believed to derive from persistence of embryologic remnants of the post anal gut (tailgut), which appears at the 3.5-mm stage of the human embryo. (1)

A few cases of true RCH have been described in the medical literature. In all cases the lesion was located within the retrorectal space, which is defined anteriorly by the rectum, posteriorly by the sacrum, superiorly by the peritoneal reflection, inferiorly by the elevator ani and coccygeus muscle, and laterally by the ureters and iliac vessels. The cysts are usually circumscribed, multilocular, and filled with cell debris or mucus. Microscopically, the cysts or locules are lined by intestinal or ciliated columnar cells, (1-3) resembling embryonic gut, although squamous and transitional cell lining has also been reported. (2,4) In addition, the cysts are characteristically surrounded by discontinuous bundles of smooth muscle and lack neural plexus. (2)

Malignancies arising in such cysts are extremely rare, with few cases reported in the medical literature. Therefore, little is known about the malignant transformation in RCH. In colonic adenocarcinoma, the transformation from an adenomatous (dysplastic) change to carcinoma is associated with several well-characterized molecular events, including the mutation in the ras oncogene and in the tumor suppressor gene p53. (5) Herein, we report 2 cases of RCH with mucinous adenocarcinoma and characterize a dysplasia-carcinoma progression in RCH by analyzing the immunoreactivity of the tumors for p53, p21, and Ki-67/ MIB-1.

REPORT OF CASES

Case 1

A 64-year-old woman presented with a 2-month history of constipation, sensation of pelvic pressure, and increased urinary frequency. She denied any gynecologic complaints or weight loss. Her medical history included a cholecystectomy, appendectomy, and ovarian cystectomy for a benign cyst, all performed approximately 20 years before this presentation. On physical examination, a mass was palpable posteriorly, protruding from below the coccyx. On rectal examination, the mass was external to the rectum and tethered in the retrorectal space. A pelvic magnetic resonance image was obtained, which demonstrated a large, presacral, circumscribed cystic mass that measured 12 x 10 cm, which displaced the rectum, uterus, and bladder anteriorly and protruded posteriorly below the coccyx. The mass was heterogeneous in nature with nonenhancing content. There was no evidence of invasion into surrounding structures. The entire colon was free of tumor. The patient underwent surgical resection of the lesion.

Case 2

A 68-year-old woman presented with a complaint of a sensation of rectal "fullness" for many years. Pelvic and rectal examination demonstrated a soft mass palpable through the posterior wall of the rectum. No intraluminal rectal mass was detected (including by sigmoidoscopic examination). No other abnormalities were detected in the cervix, uterus, ovaries, or fallopian tubes. The remainder of the physical examination was unremarkable.

Imaging studies of the pelvis, including computed tomography and magnetic resonance imaging, demonstrated a large, multiloculated cyst located in the presacral space. The mass displaced the rectum anteriorly and compressed its posterior wall. The cystic spaces showed contents of variable density, but all within the range of water or tissue density. The wall of the cyst had variable thickness. Focal calcifications were seen. No intraluminal masses were seen in the colon or rectum. No other abnormalities were seen in the pelvis, abdomen, or chest cavity.

MATERIALS AND METHODS

Histologic Testing

Representative sections were fixed in formalin and embedded in paraffin. Tissue sections were stained with hematoxylin-eosin and analyzed with a light microscope.

Immunohistologic Testing

Histologic sections were deparaffinized, rehydrated in alcohol gradient, and submitted to antigen retrieval technique. Briefly, sections were boiled using a microwave in 0.1 mol/L citrate buffer (pH 8.0) for 20 minutes. Sections were allowed to cool to room temperature in the boiling solution before immunoperoxidase staining. Study sections (with respective negative and positive controls) were stained using monoclonal antibodies to p53 antigen (Santa Cruz Biotechnology, Santa Cruz, Calif, at a dilution of 1:50), Ki-67 (Zymed Laboratories, San Francisco, Calif, 1:20), p21 protein (Oncogene Science Inc, Uniondale, NY, 1:40), cytokeratin 20 (Dako Corporation, Carpinteria, Calif, 1:20), and cytokeratin 7 (Dako, 1:50) using a diaminobenzidine detection kit (Ventana Medical Systems, Tucson, Ariz). Staining was carried out in an automated stainer (Ventana).

PATHOLOGIC FINDINGS

Case 1

The specimen consisted of a circumscribed cystic mass that measured 12 x 9 x 4 cm with a fibrous capsule. The cyst was unilocular and filled with yellow, creamy material. It also contained multiple gelatinous masses, both floating and attached to the cyst wall. The cyst lining was yellow to brown. No solid areas were identified.

Case 2

This patient underwent resection of the mass followed 6 months later by a resection of a recurrent mass. The first excision, which rendered the diagnosis of adenocarcinoma in a RCH, consisted of portions of fibromembranous, tan tissue with multilocular cysts that measured in total 18 x 4 x 2 cm. The cysts were filled with gelatinous content. The walls of the cysts were mostly membranous with variable thickness. The cyst lining was yellow and glistening. The second specimen was an abdominoperineal resection. The overall dimensions of the specimen were 36 x 9 x 7 cm. There was a bulging nodule in the perirectal fat posterior to the rectum at the level of the dentate line. Sections through the retrorectal tissue revealed a multilocular cyst with thin walls and smooth cyst lining, with the exception of one locule that measured 4.0 x 3.5 x 2.5 cm and was filled with glistening gelatinous content. There was no fistula tract to perianal skin or rectal mucosa. The tumor was confined to the retrorectal space. The colon and rectum were unremarkable.

Microscopically, the cyst walls in all cases showed discontinuous bundles of smooth muscle without a neural plexus, thus confirming the existence of an RCH (Figure 1, A). The lining of the cysts (not involved by carcinoma) showed benign squamous, cuboidal, ciliated, and mucin-secreting epithelium with goblet cells. In all cases there were foci of intense inflammatory infiltrates, rich in histiocytes within the cyst wall, consistent with cyst rupture. In addition, epithelial dysplasia consisting of a picket fence arrangement of the nuclei with focal cytologic atypia was seen in some cyst locules, adjacent or contiguous to the mucinous adenocarcinoma (Figure 1, B). In case 1, the carcinoma involved only one locule. It was moderately to poorly differentiated with abundant extracellular and intracellular mucin. In case 2, almost the entire cyst wall was lined by a well-differentiated mucinous adenocarcinoma. Invasion of the cyst wall by the adenocarcinoma was noted in both cases (Figure 1, C and D). No lymphovascular invasion was observed. No carcinoma was found in any lymph node recovered from the resection in the abdominoperineal resection specimen (case 2). Carcinoma or epithelial dysplasia was not seen in the overlying rectal mucosa.

[FIGURE 1 OMITTED]

IMMUNOHISTOLOGIC FINDINGS

There was marked overexpression of p53 in the mucinous adenocarcinoma arising in the RCH (Figure 2, A) and in the dysplastic epithelium adjacent to the tumor. In both cases there was up-regulation of the expression of MIB-1 (Ki-67 antibody), indicating a high proliferation rate in the dysplastic and malignant epithelium (Figure 2, B). To confirm that the up-regulation of both markers was a consequence of a mutated p53 gene, the sections were stained for p21 antigen, (5,7) a regulatory protein of the proliferation cycle. There was no difference in the levels of expression of p21 among the normal, dysplastic, or malignant epithelium (Figure 2, C), thus suggesting that the up-regulation of p53 expression in the adenocarcinoma was a result of a mutation in the p53 gene, which was associated with a dysregulation in cell proliferation. (6,7) In contrast, there was weak nuclear expression of p53, MIB-1, and p21 in the cells of the overlying normal rectal mucosa and in the benign lining of the RCH (not shown). The benign squamous epithelium of some locules, differently from the other epithelial lining, showed positive nuclear staining for p53, Ki-67, and p21, thus, indicating a higher proliferation rate of the benign squamous epithelium, but no mutation in the p53 gene (not shown). In addition, the cells lining the RCH and adenocarcinoma stained strongly positive for cytokeratin 20 and were negative for cytokeratin 7.

[FIGURE 2 OMITTED]

COMMENT

Retrorectal cyst hamartoma or tailgut cyst is a rare malformation of the retrorectal space. Although RCHs may be found at essentially any age group, they are most often found in mid adult life. Most RCH occurs in women, as illustrated in the present cases. Approximately half of the patients are symptomatic, with most complaining of pain in the rectal area and lower back or symptoms related to a mass effect. (2) Most of the cases of RCH in asymptomatic patients are discovered by physical examination or by imaging studies for unrelated purposes. (8)

The differential diagnosis for RCH includes teratoma, dermoid cyst, duplication cyst (enterogenous cysts), and anal gland cyst. Teratomas (sacrococcygeal teratomas) contain a much wider variety of tissues than RCH, which has a characteristic appearance consisting only of elements contained in the normal or embryonic gastrointestinal tract. (1,2) Dermoid cysts are lined by squamous epithelium only and contain skin adnexal structures and hair, which are not present in RCH. Rectal duplication cysts show the presence of all layers of the intestinal wall, including well-formed smooth muscle layers with neural plexus. Although some smooth muscle is usually present in RCH, it lacks a neural plexus. Anal gland cysts may show a lining epithelium similar to RCH, but may be distinguished by their different anatomic location (anal mucosa) and lack of associated smooth muscle.

The differential diagnosis of an adenocarcinoma arising in the RCH includes the possibility of a carcinoma arising in the colorectal mucosa with invasion into the preexisting RCH. However, careful examination of the rectal mucosa in the present cases failed to demonstrate any in situ or invasive carcinoma in the overlying rectal mucosa.

In the few reported cases of malignancies arising in an RCH, adenocarcinoma, (3,4,9) carcinoid tumors, (3,4,10) and a sarcoma (8) have been described. In the present case, the finding of dysplastic columnar epithelium within the cysts provides evidence for the site of origin of the carcinoma. Although based on the analysis of only 2 cases, the immunohistochemical study provides evidence of p53 mutation in the dysplastic epithelium, thus suggesting a common molecular event in support of a dysplasia-carcinoma sequence in RCH similar to the one described in colonic carcinomas. (5-7)

The wild-type p53 gene exerts its function as a tumor suppressor gene by encoding a protein that will induce the expression of yet another gene that regulates the cell cycle, the p21 gene, which arrests cell division. The immunostaining pattern of the squamous epithelium in the present cases illustrated the normal functioning of this complex interaction. In cells with a high proliferation rate, a wild-type p53 gene expression is associated with positive staining for p21. In the case of a mutant p53, a high proliferation rate is seen, marked by the expression of Ki67 (proliferation-associated nuclear antigen), but without the regulatory induction of p21 (negative nuclear staining). Thus, our study supports the finding of a malignant transformation in RCH associated with mutation in the tumor-inhibitory gene p53. (5-7)

The prognosis of adenocarcinomas arising in RCH is not well defined, because of the extremely small number of reported cases. Complete resection of RCH is recommended because of the possibility of the development of malignancy. In the present cases, the patient are well and disease free 10 (case 1) and 29 months (case 2) after the resection of the RCH that contained mucinous adenocarcinoma.

We thank Kenneth Eng, MD, and Elliot Newman, MD, for the clinical and follow-up information of the patients, the residents of the anatomic pathology program at New York University for examining the surgical specimens, and Herman Yee, MD, PhD, for help in preparing the figures.

References

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(2.) Hjermstad BM, Helwig EB. Tail gut cysts: report of 53 cases. Am J Clin Pathol. 1988;89:139-147.

(3.) Marco V, Autonell JA, Farre J, Fernandez-Layos M, Doncel F. Retrorectal cyst-hamartomas: report of two cases with adenocarcinoma developing in one. Am J Surg Pathol. 1882;6:707-714.

(4.) Prasad AR, Amin MB, Randolph TL, Lee CS, Ma CK. Retrorectal cystic hamartoma: report of 5 cases with malignancy arising in 2. Arch Pathol Lab Med. 2000;124:725-729.

(5.) Ieda S, Watatani M, Yoshida T, Kuroda K, Inui H, Yasutomi M. Immunohistochemical analysis of p53 and ras p21 expression in colorectal adenocarcinomas and early carcinomas. Surg Today. 1996;26:230-235.

(6.) Doglioni C, Pelosio P, Laurino L, et al. P21/WAF1/CIP1 expression in normal mucosa and in adenomas and adenocarcinomas of the colon: its relationship with differentiation. J Pathol. 1996;179:248-253.

(7.) Tominaga O, Nita ME, Nagawa H, Fujii S, Tsuruo T, Muto T. Expression of cell cycle regulators in human colorectal cancer cell lines. Jpn J Cancer Res. 1997;88:855-860.

(8.) Moulopoulos LA, Karvouni E, Kehagias D, Dimopoulos MA, Gouliamos A, Vlahos L. MR imaging of complex tail-gut cysts. Clin Radiol. 1999;54:118-122.

(9.) Graadt van Rogen JF, Welvaart K, de Roos A, Offerhaus GJA, Hogendoorn PCW. Adenocarcinoma arising within a tailgut cyst: clinicopathological description and follow up of an unusual case. J Clin Pathol. 1999;52:310-312.

(10.) Horenstein MG, Erlandson RA, Gonzales-Cueto DM, Rosai J. Presacral carcinoid tumors: report of three cases and review of the literature. Am J Surg Pathol. 1998;22:251-255.

Accepted for publication March 30, 2001.

From the Department of Pathology, New York University Medical Center, New York, NY.

Reprints: Jonathan Melamed, MD, Department of Pathology, New York University Medical Center, 560 First Ave, New York, NY 10016 (e-mail: [e-mail]).