Histopathology of borderline and early malignant melanomas
Two groups of patients with pigmented lesions of the skin of borderline malignancy have been described. The first was characterized by an atypical intraepidermal melanocytic hyperplasia and the second, by an early invasive form of superficial spreading malignant melanoma, less than 0.76 mm in tumor thickness and of low risk. The sites of occurrence were similar in the two groups. The mean age of the 228 patients in the atypical hyperplasia group was 38 years, whereas that of the 148 patients in the superficial melanoma group was 44 years. Within the spectrum of atypical melanocytic hyperplasias, three patterns were defined: atypical intraepidermal melanocyte hyperplasia 1) without cellular host response; 2) with host response; and 3) with host response and microinvasion. The first pattern was found in 40 of the 228 cases, the second in 158 cases, and the third in 30 cases. An associated benign pigmented nevus was found in 50% of the total atypical hyperplasia group and 53% of the superficial melanoma group. Atypical melanocytic hyperplasia can be distinguished from various forms of benign melanocytic hyperplasia, including lateral lentigionus extension adjacent to enlarging but benign nevi, the more usual form of benign lentigo, and the Spitz nevus, or spindle cell/epithelioid cell nevus. The association of atypical melanocyte hyperplasia with malignant melanoma is discussed, together with some therapeutic implications of the observations.