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Extranodal Follicular Dendritic Cell Tumor of the Abdominal Wall

Roderich E. Schwarz, Peiguo Chu, Daniel A. Arber

City of Hope National Medical Center, Departments of General Oncologic Surgery and Anatomic Pathology, Duarte, CA

A 62-year-old man presented with a lower abdominal mass and some abdominal and left-sided groin pain. Computed tomography showed that this mass extended maximally to 15 cm in diameter, arose from the anterior abdominal wall, and lacked visceral involvement despite an intra-abdominal expansile growth (Fig 1A and 1B). The remaining examination and laboratory and imaging workup did not suggest the presence of metastatic disease. A fine-needle aspiration of the mass was consistent with a poorly differentiated sarcoma. The patient underwent operative treatment, with excision of some overlying skin, and radical resection of the soft tissue mass. Although displaced by tumor from the abdominal wall, the parietal peritoneum was not violated (Fig 2). Closure involved a dual mesh reconstruction. Pathologic analysis revealed a fleshy tan neoplasm with focal necrosis and negative surgical margins (Fig 3). Histologic examination demonstrated a spindle cell neoplasm with a whorling storiform pattern (Fig 4). The immunohistochemical staining pattern, including CD21 positivity (Fig 5) and CD35 positivity (Fig 6), was consistent with a follicular dentritic cell tumor (FDCT). The patient, who recovered uneventfully and underwent adjuvant external-beam radiation therapy to the abdominal wall, is currently disease-free after 8 months.

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Follicular dendritic cells (FDCs) are found in primary and secondary lymphoid follicles and play an essential role in antigen presentation for the B-cell compartment, as well as regulation of the germinal center reaction.¹ The exact origin of FDCs remains unclear, and hematopoietic lineage origin or stromal-cell derivation have been proposed. Proliferation of FDCs can lead to benign reactive lesions or generate neoplastic conditions. The diagnosis of a FDCT can be made based on immunohistochemical CD21 and CD35 positivity and/or characteristic ultrastructural findings of long, complex, and occasionally interdigitating cytoplasmic processes joined by desmosomes.²

After initial case descriptions of tumors arising from follicular dendritic reticulum cells within lymphatic tissues,^3-5 FDCTs have been increasingly recognized as a specific oncologic entity.^6,7 The term follicular dendritic cell sarcoma is also used to describe the same entity. Fifty-one cases of FDCT have been described to date,⁸ and most of them have arisen in lymphatic tissue, primarily of the neck.⁹

Intra-abdominal tumor location can involve the liver, spleen, or pancreas, in addition to the mesenteric or retroperitoneal lymph nodes. FDC proliferations may also be associated with the hyaline-vascular type of Castleman disease or, rarely, Epstein-Barr virus–positive hepatic or splenic inflammatory pseudotumors.¹⁰ Only two patients with soft tissue FDCTs, both arising in the neck, have been described,⁶ but it is unclear whether these tumors originated in lymphatic tissue as well. Because FDCs normally occur only in lymphoid follicles, we assume that even the FDCT of our patient likely arose from lymphatic tissue within the abdominal wall, rather than in a truly "extranodal" tissue site.

The immunohistochemical diagnosis of FDCT relies on markers characteristically expressed on FDCs, including CD21 and CD35, which recognize complement receptors C3d and C3b, respectively.⁷ In that sense, FDCTs are clearly distinct from interdigitating reticulum cell sarcomas (IRCSs) (CD45RB-negative, S100 protein-negative, and histiocytic marker–positive), of which 21 cases have been described to date.⁸ The clinical or histopathologic distinction between IRCSs and FDCTs may be quite difficult to make. IRCSs may display a more aggressive course.⁸ The clinical behavior of FDCTs resembles that of soft tissue sarcomas rather than that of lymphomas, with local recurrences in 36% and metastases in 28%.⁷ Intra-abdominal location has been linked to a worse prognosis.⁶ Although the optimal treatment for FDCT is not known because of the limited experience, it seems sensible to apply therapeutic guidelines similar to those used for soft tissue sarcomas of high grade. Complete surgical resection is the therapy of choice, with the possibility of adjuvant radiation or chemotherapy for large or deep lesions.⁷ Responses to "sarcoma-type" systemic treatment have been observed that should be considered in cases with high-risk clinicopathologic features.⁶ Our case illustrates that FDCT can occur within soft tissue without intimate proximity to major nodal drainage basins and that FDCT should be included in the differential diagnosis of soft tissue neoplasms. The optimal combination treatment for FDCT has yet to be defined.

REFERENCES

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