Malignant transformation of mastocytoma developed on skin mastocytosis into cutaneous mast cell sarcoma.

Mastocytosis is a group of disorders characterized by abnormal mast cell proliferation, involving the skin in 80% of cases. Cutaneous mastocytosis, which appears in childhood in 60% of cases, usually has a benign course with a gradually regressive evolution before puberty. Mast cell sarcomas, part of the systemic forms of mastocytosis, are very rare tumors characterized by a destructive growth of highly atypical mast cells, with secondary spread, poor prognosis, and low survival rates. We report the first known case of primary cutaneous mast cell sarcoma due to the transformation of a benign solitary mastocytoma in an adult suffering from an unregressive localized cutaneous mastocytosis. Histologic characteristics of the tumor, mutation analysis, and c-Kit expression were compared with available data. Wide surgical excision of the tumor followed by adjuvant local radiotherapy were performed, and for the first time the use of imatinib was attempted, as neoplastic mast cells expressed the CD117 marker. However, they failed to control the progression of sarcoma. To date, no treatment is known to be effective for this disease, which is associated with short-term survival of the patients.