P53 EXPRESSION IS RARE IN CUTANEOUS MELANOMAS

Alterations in the tumor-suppressor gene p53 are common in many types of human malignancies, but the potential role of p53 in the pathogenes is of cutaneous melanoma is controversial. The gene product, p53 prote in, is normally present in very small amounts in noncancerous tissues. Missense mutations lead to accumulation of mutant p53 in the cells, w hich makes it detectable immunohistochemically in many cancers. Formal in-fixed, paraffin-embedded sections of 14 primary invasive melanomas, 3 cutaneous melanoma metastases, and 10 predominantly intradermal mel anocytic nevi were reacted with a panel of three anti-p53 monoclonal a ntibodies (mAbs) (PAb240, PAb1801, and DO7) and a mAb against Ki-67 (M IB-1), a marker of cellular proliferation. p53 was not detected in mor phologically normal epidermal melanocytes or nevus cells. A single pri mary invasive melanoma, having a very high index of proliferation (Ki- 67 expression in >50% of cells), had diffuse nuclear labeling with all three anti-p53 mAbs used. Abnormalities of p53 expression occur rarel y in cutaneous melanomas, but overexpression of p53 may occur in a sub set of melanomas with a high index of proliferation.