P53 ONCOPROTEIN EXPRESSION AND PROLIFERATION INDEX IN KERATOACANTHOMAAND SQUAMOUS-CELL CARCINOMA

Background and Design: Whether solitary keratoacanthoma (KA) is a mali gnant neoplasm despite its self-limited clinical behavior, and the dis tinction between KA and squamous cell carcinoma (SCC) are related aspe cts of a long-standing debate among dermatopathologists. Recent advanc es toward understanding the molecular basis of malignant transformatio n may allow this issue to be resolved. Mutant p53 tumor-suppressor pro tein has been shown to accumulate in cutaneous SCC and other tumors, a nd may be a relatively specific marker of malignancy. We studied 20 SC Cs, 20 KAs, and an additional 10 regressing KAs (rKA) by immunohistoch emistry for the expression of p53 protein. Since p53 is believed to pl ay a pivotal role in the regulation of cell division, we also quantita ted proliferation in the tumors by examining Ki-67 antigen expression. Results: Sixteen (80%) of the KAs showed nuclear staining with anti-p 53 antibody, distributed along the outermost layers of the aggregates of neoplastic cells, while 12 (60%) of the SCCs were p53 positive. Eig ht (80%) of the rKAs also showed p53 positivity. Mean Ki-67 proliferat ion fraction was higher for KA than for SCC (55% vs 46%), but this dif ference was not statistically significant. p53 Expression did not corr elate with the grade of SCC. Conclusions: A majority of KA, rKA, and S CC contain stainable quantities of p53 protein, supporting the view th at KA is a type of regressing SCC.