Utility of a proliferation marker in distinguishing between benign naevocellular naevi and naevocellular naevus-like lesions with malignant properties.

In the present study we have investigated the utility of the proliferation marker MIB 1 in distinguishing between benign naevocellular naevi and naevocellular naevus-like lesions with malignant potential. Percentages of MIB 1 immunoreactivity in the intradermal portion of the lesions were determined. In benign congenital and acquired naevi, as well as in dysplastic naevi, there was no or only a slight intradermal melanocytic proliferation (0-2%), whereas vertical growth phase melanomas exhibited a substantial proliferative activity (11-48%). In five cases of naevus-lke lesions, which had all relapsed as unmistakable malignant melanomas (locally or metastatically) after primary surgery, there was also clear proliferative activity (9-67%). Our findings suggest that MIB 1 may be a useful tool in the routine histopathological examination of problematic naevocellular lesions.