Malignant cellular blue nevus: a clinicopathological study of 6 cases.

BACKGROUND: Malignant cellular blue nevus (MCBN) is a rare entity due to the malignant transformation of a preexisting cellular blue nevus (CBN). OBJECTIVE and METHODS: The clinical and pathologic features of 6 patients with MCBN are described. RESULTS: Three tumors were located on the scalp, 2 on the trunk and 1 on the neck. The lesions, present from birth or childhood, had enlarged rapidly in the last months before excision. Histologically, there was a dermal proliferation of spindle and epithelioid atypical melanocytic cells. Some of them were heavily pigmented. Numerous atypical mitoses were seen. In 2 cases, foci of necrosis were detected. In 2 cases, remnants of CBN were also noted. MCBN has a poor prognosis and may be difficult to differentiate from so-called atypical blue nevus, metastasis of malignant melanoma and malignant transformation of combined nevus. CONCLUSIONS: CBN may represent a precursor of malignant melanoma. In MCBN, malignant changes seem to occur in clear cells.