Sarcomatoid tumours of lymph nodes showing follicular dendritic cell differentiation.

Putative sarcomas of follicular dendritic cells are extremely uncommon and only small case numbers have been clearly documented. A major difficulty in their delineation has been the persistent controversy over the phenotype and ontogeny of normal follicular dendritic cells. Two new cases arising in adult females are presented herein, both of which had initially been mistaken for metastases from a true soft tissue sarcoma. Their morphology, immunophenotype, and ultrastructure (in one case) are described in order to aid their wider recognition. In the light of these findings, the nature and origin of follicular dendritic cells are discussed.