Unusual Presentation of a Rare Tumor: Histiocytic Sarcoma Presenting as a Finger Growth.

Histiocytic sarcoma (HS) is a malignant neoplasm with histiocytic differentiation. It presents most commonly at extranodal sites. We report a case of HS in a 15-year-old female with a history of trauma to the right little finger. Radiograph of the hand was reported as malignant tumor primarily arising from bone and invading soft tissues. Histologically, tumor cells are characterized by abundant eosinophilic cytoplasm and eccentric round to oval nuclei with atypia. One or more small and distinct nucleoli are present. The tumor cells were positive for CD68, S100, CD4 and lymphocyte common antigen, while epithelial membrane antigen, HMB-45, CK AE1/AE3, myogenin, desmin, CD1a, CD21 and SALL-4 were negative thus ruling out rhabdomyosarcoma, extrarenal rhabdoid tumor, Langerhans cell sarcoma and malignant melanoma.