Mast cell sarcoma: a rare and potentially under-recognized diagnostic entity with specific therapeutic implications.

[cutaneous mastocytosis]

Mast cell sarcoma is a rare , aggressive neoplasm composed of cytologically malignant mast cells presenting as a solitary mass . Previous descriptions of mast cell sarcoma have been limited to single case reports , and the pathologic features of this entity are not well known . Here , we report three new cases of mast cell sarcoma and review previously reported cases . Mast cell sarcoma has a characteristic morphology of medium-sized to large epithelioid cells , including bizarre multinucleated cells , and does not closely resemble either normal mast cells or the spindle cells of systemic mastocytosis . One of our three cases arose in a patient with a remote history of infantile cutaneous mastocytosis , an association also noted in one previous case report . None of our three cases were correctly diagnosed as mast cell neoplasms on initial pathological evaluation , suggesting that this entity may be under-recognized . Molecular testing of mast cell sarcoma has not thus far detected the imatinib-resistant KIT D 816 V mutation , suggesting that recognition of these cases may facilitate specific targeted therapy .