EXTRANODAL FOLLICULAR DENDRITIC CELL-SARCOMA OF THE GASTROINTESTINAL-TRACT - MORPHOLOGIC, IMMUNOHISTOCHEMICAL AND ULTRASTRUCTURAL ANALYSIS OF 2 CASES

Tumors showing differentiation toward follicular dendritic cells are r are and usually occur in lymph nodes. Their occurrence at extranodal s ites was recognized recently. This report documents two further extran odal cases, one arising in the small intestine of a 23-year-old woman and the second in periduodenal retroperitoneal soft tissue of a 63-yea r-old man, Both neoplasms displayed a typical biphasic morphologic pat tern, composed of large cells with indistinct cytoplasmic borders crea ting a syncytial appearance, admired with spindle cell areas resemblin g malignant fibrous histiocytoma, and infiltrated by numerous small T lymphocytes, Expression of CD21 and CD35, together with ultrastructura l demonstration (in one case) of long cytoplasmic processes connected by desmosomes, confirmed follicular dendritic cell differentiation. On e case also expressed HLA-DR, and both showed aberrant epithelial memb rane antigen staining, Neither tumor showed CD45 expression. In both c ases the tumors were treated by local excision, Case 1 has shown an un usually aggressive course with extensive intraperitoneal recurrence. T he biphasic morphologic pattern and tumor immunophenotype are discusse d in relation to increasing evidence of immunophenotypic and morpholog ic heterogeneity of normal follicular dendritic cells.