Extranodal Follicular Dendritic Cell Sarcoma: Clinicopathologic and Immunohistochemical Profile of a Rare Sarcoma

Background: Follicular Dendritic Cell Sarcoma (FDCS) is a rare malignant neoplasm characterized by spindled-to-ovoid cells exhibiting morphological and immunophenotypic features of follicular dendritic cells.FDCS can occur in both nodal and extranodal sites. Methods:We identified nine cases of FDCS from pathology archives over a period of 30 years.From these nine cases, we did a comprehensive evaluation, including histology, immunostains, imaging, and clinical data. Results:We identified 9 FDCS cases, including 3 male and 6 female patients (M:F ratio of 1:2).Median age was 67 years (range: 40-89).All patients were of Caucasian ethnicity.The tumors presented in diverse locations: neck soft tissue (2 cases), perigastric area (1 case), mediastinum (2 cases), gluteal area (1 case), liver (1 case), thigh mass (1 case), and pancreas (1 case).Immunohistochemical analysis consistently demonstrated CD21 and CD23 positivity in all cases, with clustering in 6 cases.Epstein-Barr virus-encoded small RNA (EBER) in situ hybridization studies were performed on 3 cases and were negative.No cases exhibited immunoreactivity for keratin markers or S100.Remarkably, one case presented as a pancreatic mass, prompting a Whipple procedure.Castleman disease was absent.Six cases (67%) developed distant metastasis to various sites, including the pleura (2 cases), prehepatic tissue, peritoneum, ileum (1 case), liver (2 cases), and mediastinum. Conclusion:These nine FDCS cases highlight the clinical and pathological diversity of this exceedingly rare malignancy.FDCS occurring in atypical anatomical sites, such as the pancreas, accentuates diagnostic complexities.Furthermore, the absence of Castleman disease underscores the need for meticulous differentiation.