Extranodal follicular dendritic cell sarcoma: clinical, pathologic, and histogenetic characteristics of an underrecognized disease entity.

It has been more than 10 years since follicular dendritic cell (FDC) sarcoma was first reported to occur in extranodal sites, yet extranodal FDC sarcoma still appears underrecognized, and its clinical and pathological characteristics remain to be defined. This study analyzed the clinical and pathological findings of three such cases that the authors encountered recently and 43 previously reported cases identified in the literature. Assessment of all 46 cases showed a slight female predominance (1.2:1) with a median age of 41.5 years. One-third of the cases were misdiagnosed at initial evaluation mainly because the possibility of FDC sarcoma was not considered. When considered, this disease had distinct pathological characteristics that allowed an accurate diagnosis. Staining for FDC markers, CD21, CD35, and clusterin was particularly helpful. The pathogenesis of the disease appeared heterogeneous, and associated factors included Epstein-Barr virus infection (in hepatic cases) and inflammatory pseudotumor-like conditions. Treatment modality varied widely although surgical resection was often included. With a median follow-up of 18 months, 43% of the cases recurred and 7% died of disease. The 5-year recurrence-free survival was 27.4%. From data available at the current time, we were not able to identify prognostically significant pathologic factors.