Regressing malignant melanoma.

: Malignant melanoma may undergo spontaneous regression. This phenomenon may cause difficulty in clinical or pathologic diagnosis. The cases reported in the literature as complete spontaneous regression of primary malignant melanomas have been diagnosed only in retrospect, after the patient presented with metastatic malignant melanoma. Two cases of malignant melanoma with partial regression are reported. In these cases the areas of complete regression cannot be recognized as malignant melanoma. The definitive diagnosis of malignant melanoma can be made only in the areas with at least two of three characteristic features of melanoma, (1) melanocytic cells with atypical nuclei and prominent nucleoli, (2) mitoses in melanocytic cells, and (3) invasion of the epidermis by atypical melanocytic cells. Clinical features suggesting regressing malignant melanoma include changes in color, especially areas of depigmentation, variations in color in different areas of a pigmented mole, and decrease in size of a mole. Histopathologic features of regression include loss of melanin pigment from the epidermis, melanophages in the dermis, telangiectasia of capillaries in the dermis, and lymphocytic infiltration in the dermis in a band-like or perivascular pattern. These histologic findings may also be found in inflammatory lesions such as lichen planus and in regressing benign melanocytic nevi.