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Follicular Dendritic Cell Sarcoma.

Follicular dendritic cell sarcoma (FDCS) was first described in 1986 by Monda et al, (1) in a series of 4 cases with initial presentation of unilateral cervical adenopathy, as a nonlymphomatous primary lymph node malignancy with features suggesting dendritic reticulum cell origin. Follicular dendritic cell sarcoma is a neoplastic proliferation of spindled to ovoid cells with morphologic and immunophenotypic features similar to those of normal follicular dendritic cells and is classified under histiocytic and dendritic cell neoplasms by the World Health Organization Classification of Tumours. (2) Follicular dendritic cells are normally present in both nodal and extranodal lymphoid follicles and serve as antigenpresenting cells to B-cell lymphocytes, serving an important role in B-cell migration, proliferation, and differentiation. (3) In addition to storing antigens as cell surface immune complexes for long periods of time, follicular dendritic cells are a nonmigrating population likely derived from the stroma that assist in the architectural support of the lymphoid follicles via cellto-cell attachments and desmosomes. (4,5)


There is a wide age range associated with FDCS, mostly affecting young to middle-aged adults (mean age, 44 years; median age in the fifth decade) of both sexes, although there is a female predilection for the inflammatory pseudotumorlike variant of FDCS, an uncommon and distinct variant of FDCS. (2) There is also the possibility that FDCS may occur more among certain ethnicities or in certain geographic locations because many cases have been reported from East Asia. (6)

Most cases do not have a known etiology. Human herpesvirus 8 is not associated with FDCS. (7) The inflammatory pseudotumor-like variant of FDCS is an uncommon tumor that is consistently associated with the Epstein-Barr virus. It has selective involvement to the liver and spleen and is characterized by marked female predominance and frequent presence of systemic symptoms. (8) Epstein-Barr virus-encoded RNA is found in almost all neoplastic cells, and Southern blot studies have shown that the virus has a monoclonal episomal form. (2)

Approximately 10% to 20% of FDCS cases are associated with antecedent or concurrent Castleman disease, a benign lymphoproliferative disorder, mostly the hyaline vascular variant (Figure 1). Some cases of antecedent Castleman disease demonstrate areas of follicular dendritic cell proliferation, and FDCS is hypothesized to arise in these areas. (9) Additionally, a shared feature of Castleman disease and FDCS is expression of epidermal growth factor receptor (EGFR). (10)


Most patients generally present with an asymptomatic, slow-growing, painless cervical lymphadenopathy. Approximately one-third of FDCS cases occur in extranodal sites, including skin, mediastinum, tonsil, gastrointestinal tract, and soft tissue. (11,12) Most cases are asymptomatic, although patients with abdominal disease may present with abdominal pain, and systemic symptoms can include fatigue, fever, and night sweats.

Additionally, there may be an association between FDCS and autoimmune disease: paraneoplastic pemphigus and myasthenia gravis. Paraneoplastic pemphigus has been seen in patients with FDCS, either with or without evidence of previous Castleman disease. (13,14) There have also been at least 6 reports of FDCS in patients with concurrent diagnoses of myasthenia gravis. Their tumors show aggregates of small lymphocytes composed of predominantly immature T cells, which are uncharacteristic of FDCS. This suggests another paraneoplastic manifestation of FDCS. (6,15)


Follicular dendritic cell sarcomas are characteristically well circumscribed or even encapsulated, bosselated masses that are solid with pink or white to tan-grey cut surfaces. The size has been reported to range from 1 to 15 cm, largely dependent on the tumor location, with a median size of approximately 5 cm. (9,16) The average size of extranodal tumors is 7.4 cm with a range from 1 to 20 cm. (17) Larger tumors may show necrosis or gross hemorrhage.


Most FDCSs are considered low-grade sarcomas. Histologic sections demonstrate a spindle cell proliferation with a varied architectural pattern in storiform (most common) or whorled (meningioma-like) bundles, fascicles, trabecular, or diffuse sheets (Figure 2). (18) Several growth patterns can often be seen in the same tumor. Prominent lymphocytes can be spread throughout the tumor in between tumor cells and in perivascular spaces, with some cases predominantly B-cell lymphocytes and other cases predominantly T-cell lymphocytes. Scattered multinucleated cells, although in small numbers, can be seen and can resemble Warthin-Finkeldey giant cells. (9) The cell borders are generally indistinct, imparting a syncytial appearance, and the cytoplasm is moderately abundant, lightly eosinophilic, and can have a fibrillary quality. The tumor cells have elongated or ovoid nuclei with a thin nuclear membrane, vesicular or granular chromatin, and small nucleoli. Nuclear pseudoinclusions can occasionally be seen, with frequency increased after radiation therapy. (19) Mitotic rate is usually low with 0 to 10 mitoses per 10 high-power fields and necrosis is not commonly seen. Most cases are relatively bland and uniform but cytologic atypia may be seen in some cases with pleomorphic cells (Figure 3).

High-grade histologic features may include significant cellular atypia (irregular nuclear membranes and large hyperchromatic nuclei), high mitotic count (reported cases of 11 to 35 mitoses per 10 high-power fields), and extensive necrosis. (16) High-grade features are associated with deep-seated lesions and recurrent or metastatic lesions. (9)

The inflammatory pseudotumor-like follicular dendritic cell tumor is a variant of FDCS with distinct histologic features. This variant shows a loose fascicular and sheetlike growth pattern of spindle or ovoid cells with vesicular nuclei in a background of abundant lymphocytes and plasma cells. (8) Nuclear atypia can be variable with some nuclei resembling Reed-Sternberg cells.

Cytomorphology of FDCS is characteristic but may be difficult to recognize, and often requires further confirmation with immunohistochemical studies. Aspiration cytology of a lesion will show large, spindle to ovoid epithelioid cells singly, in small clusters, and in syncytial sheets; moderate to abundant cytoplasm; indistinct cell borders; irregular nuclear membranes; fine to vesicular chromatin; and conspicuous nucleoli. (20)


Immunohistochemical studies are essential in the diagnosis of FDCS (Figure 4, a through c). Nodal and extranodal FDCSs have similar immunophenotypes. Follicular dendritic cell sarcomas generally demonstrate the immunophenotype of nonneoplastic follicular dendritic cells and are usually positive for dendritic cell markers CD21 (C3b complement receptor), CD23, and/or CD35 (C3d complement receptor), exhibiting cell membrane staining, although cytoplasmic staining can also be seen. (9,18,21) Clusterin is a glycoprotein associated with many cellular functions, including apoptosis, and shows strong positivity in follicular dendritic cell tumors with weak to no expression in other dendritic cell tumors. (22) Strong diffuse clusterin staining has high specificity and sensitivity for FDCS. (23) Podoplanin (D2-40) is another marker shown to have high sensitivity for FDCS with strong membranous staining. (24) [gamma]-Synuclein is a relatively recent marker shown to strongly stain follicular dendritic cell meshwork and may also be considered helpful in identifying FDCS. (25)

Additionally, the tumor is usually positive for vimentin, fascin, desmoplakin, EGFR, and human leukocyte antigenDR. It is variably positive for epithelial membrane antigen, S100, and CD68, which can present diagnostic pitfalls. Staining for CD1a, lysozyme, myeloperoxidase, CD34, CD3, CD79a, CD30, HMB-45, desmin, and high-molecular weight cytokeratins is negative. Ki-67 labeling ranges from 1% to 25%.2,9


Diagnostic ultrastructural features of FDCS include long, slender, interdigitating cytoplasmic processes, sometimes producing a labyrinth-like pattern and desmosome-like junctions (Figure 5). (18) The cytoplasm often contains few organelles. Birbeck granules and lysosomes are not seen.


Follicular dendritic cell sarcoma has no B-cell or T-cell gene rearrangements and only isolated cases of cytogenetic abnormalities have been reported. Based on the literature, it seems that FDCS is frequently associated with complex cytogenetic abnormalities, although consistent or specific aberration has not been established to date in this entity.

Recently, a multicenter study performed by Go et al (26) examined the BRAF pathway and its contribution to the pathogenesis of histiocytic and dendritic cell neoplasms, including FDCS. Through direct Sanger sequencing, as well as peptide nucleic acid clamp quantitative polymerase chain reaction, the authors found that the [BRAFV.sup.600E] mutation was positive in 18.5% (5 of 27) of FDCS cases, and in both conventional as well as inflammatory pseudotumor-like types. Notably, [BRAFV.sup.600E] was found in 40% (2 of 5) of inflammatory pseudotumor-like subtypes. The authors note that BRAF mutations could potentially help differentiate inflammatory pseudotumor-like FDCS from inflammatory myofibroblastic tumor. (26)


Follicular dendritic cell sarcoma can often be misdiagnosed, with reports of 30% to 58% misdiagnosed cases, especially when arising from extranodal sites. (11,17) Differential diagnoses of FDCS include interdigitating dendritic cell sarcoma, thymoma, spindle cell carcinoma, metastatic undifferentiated carcinomas, malignant melanoma, and gastrointestinal stromal tumor (GIST). Interdigitating dendritic cell sarcomas are rare entities and usually arise from lymph nodes or the spleen, and thus may be considered a differential diagnosis for FDCS when a lesion arises from those sites. Interdigitating dendritic cell sarcomas have a paracortical distribution in lymph nodes and lack the storiform and whorled patterns of FDCS. (27) Unlike FDCS, interdigitating dendritic cell sarcomas are diffusely positive for S100, negative for dendritic cell markers (CD21, CD35), and lack desmosomes on electron microscopy. When arising from the mediastinum, a FDCS can be confused with a thymoma because of similar histomorphology, but thymomas stain for cytokeratins and p63 and do not express follicular dendritic cell markers. A helpful morphologic distinguishing feature is the presence of Hassall corpuscles in thymomas. Spindle cell carcinomas also express cytokeratin positivity. Follicular dendritic cell sarcoma with epithelial membrane antigen expression may be mistaken for metastatic undifferentiated or sarcomatoid carcinomas; however, FDCSs are usually negative for cytokeratins. (27) Malignant melanomas are positive for HMB-45 and Melan-A. Follicular dendritic cell sarcomas arising in the gastrointestinal tract may be mistaken for KIT-negative GIST but dense lymphocytic infiltrates are uncommon in GIST; GIST is also negative for CD21 and CD35, whereas FDCS is negative for CD34 and DOG1. (27) Other entities that should be considered in the list of differential diagnoses include sarcomas such as malignant fibrous histiocytoma, malignant peripheral nerve sheath tumors, histiocytic sarcoma, and carcinomas, particularly lymphoepithelioma-like carcinomas.

The inflammatory pseudotumor-like variant of FDCS that arises in the liver and spleen can resemble inflammatory myofibroblastic tumor. It is positive for Epstein-Barr virus-encoded RNA. The location of the tumor is helpful in diagnosis. Also, unlike FDCS, inflammatory myofibroblastic tumor is positive for smooth muscle actin, may express desmin, and 50% are positive for ALK, with ALK gene arrangements. (27)

In the right context, a high index of suspicion is required in the diagnosis of FDCS and should be seriously considered when there is an unusual-appearing cytokeratin-negative neoplasm, thymoma-like tumor presenting outside the mediastinum, meningioma-like tumor outside the dura, and GIST rich in lymphoid cells. (18) It is important to remember that FDCS has a distinctive immunophenotype, and the absence of cytokeratin staining can rule out many carcinoma entities. Also, expression of dendritic cell markers is very specific.


Follicular dendritic cell sarcoma has a variable clinical course and there is no uniform treatment strategy at present. Follicular dendritic cell sarcoma was traditionally considered to act like a low-grade neoplasm. However, further studies with longer follow-up periods, and the recognition of increased cytologic atypia, have indicated that FDCS is a more high-grade lesion, or at the very least an intermediategrade lesion characterized by local recurrences and occasional distant metastases. While the role of radiation therapy and chemotherapy is not well defined, complete surgical resection appears to be the treatment of choice for both primary and recurrent lesions. (6,16)

For FDCSs with the [BRAF.sup.V600E] mutation, there is potential for vemurafenib, a BRAF enzyme inhibitor, as a targeted therapy as it was shown to exhibit dramatic effects in other dendritic and histiocytic neoplasms such as Erdheim-Chester disease and Langerhans cell histiocytosis. (28) Another potential class of therapeutic agents is EGFR inhibitors, particularly in cases with moderate to strong expression of EGFR. (10)

Local recurrences are common, occurring in approximately 40% to 50% of cases. Tumors arising in lymph nodes are often indolent, with low rate of metastases (approximately 10%), whereas extranodal tumors, especially abdominal tumors, have higher metastatic potential (>20%). Common metastatic sites include liver, lung, and lymph nodes. Unfavorable prognostic factors include intra-abdominal location, large tumor size (greater than 6 cm), coagulative necrosis, mitotic count greater than 5 mitoses per 10 high-power fields, and significant cellular atypia, with intraabdominal location the single most important unfavorable prognostic factor. (2,16,17,19,27) Although for many patients the disease responds to treatment, the relapse rate can be as high as 80%. (21) The mortality rate is approximately 20%, usually after a protracted course.


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(23.) Grogg KL, Macon WR, Kurtin PJ, Nascimento AG. A survey of clusterin and fascin expression in sarcomas and spindle cell neoplasms: strong clusterin immunostaining is highly specific for follicular dendritic cell tumor. Mod Pathol. 2005; 18(2):260-266.

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(25.) Zhang H, Maitta RW, Bhattacharyya PK, et al. [gamma]-Synuclein is a promising new marker for staining reactive follicular dendritic cells, follicular dendritic cell sarcoma, Kaposi sarcoma, and benign and malignant vascular tumors. Am J Surg Pathol. 2011; 35(12):1857-1865.

(26.) Go H, Jeon YK, Huh J, et al. Frequent detection of BRAF(V) (600E) mutations in histiocytic and dendritic cell neoplasms. Histopathology. 2014; 65(2):261-272.

(27.) Hornick JL. Soft tissue tumors with prominent inflammatory cells. In: Hornick J, ed. Practical Soft Tissue Pathology: A Diagnostic Approach. Philadelphia, PA: Elsevier Saunders; 2013:257-261.

(28.) Haroche J, Cohen-Aubart F, Emile JF, et al. Dramatic efficacy of vemurafenib in both multisystemic and refractory Erdheim-Chester disease and Langerhans cell histiocytosis harboring the BRAF V600E mutation. Blood. 2013; 121(9):1495-1500.

Annie Wu, MD; Sheeja Pullarkat, MD

Accepted for publication November 24, 2014.

From the Department of Pathology & Laboratory Medicine, David Geffen School of Medicine at UCLA, Los Angeles, California.

The authors have no relevant financial interest in the products or companies described in this article.

Reprints: Annie Wu, MD, Department of Pathology & Laboratory Medicine, David Geffen School of Medicine at UCLA, 10833 Le Conte Ave, Room 13-145G, Los Angeles, CA 90095-1732 (e-mail:

Caption: Figure 1. Castleman disease hyaline vascular variant demonstrating regressed follicles with penetrating vessel and vascular proliferation (hematoxylin-eosin, original magnification X200).

Caption: Figure 2. Follicular dendritic cell sarcoma, with highly cellular areas showing varied fascicular, whorled, and storiform architecture, low- and high-power (inset) views (hematoxylin-eosin, original magnifications X40 and X200 [inset]).

Caption: Figure 3. High-grade features in a follicular dendritic cell sarcoma with cellular atypia including irregular nuclear membranes and large hyperchromatic nuclei (hematoxylin-eosin, original magnification with oil X1000).

Caption: Figure 4. Immunohistochemical profile of follicular dendritic cell sarcoma including (a) [CD23.sup.+] cells, (b) variable CD68 staining, and (c) epidermal growth factor receptor staining (original magnification X200 [a through c]).

Caption: Figure 5. Electron micrograph of follicular dendritic cell sarcoma shows well-developed, long interdigitating cytoplasmic processes and desmosome-like junctions; no Birbeck granules are seen (original magnification X20 000).

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Author:Wu, Annie; Pullarkat, Sheeja
Publication:Archives of Pathology & Laboratory Medicine
Date:Feb 1, 2016
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