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February 1994

p53 Oncoprotein Expression and Proliferation Index in Keratoacanthoma and Squamous Cell Carcinoma

Author Affiliations

From the Departments of Pathology (Drs Kerschmann, McCalmont, and LeBoit) and Dermatology (Drs LeBoit and McCalmont), University of California at San Francisco.

Arch Dermatol. 1994;130(2):181-186. doi:10.1001/archderm.1994.01690020047007

Background and Design:  Whether solitary keratoacanthoma (KA) is a malignant neoplasm despite its self-limited clinical behavior, and the distinction between KA and squamous cell carcinoma (SCC) are related aspects of a long-standing debate among dermatopathologists. Recent advances toward understanding the molecular basis of malignant transformation may allow this issue to be resolved. Mutant p53 tumor-suppressor protein has been shown to accumulate in cutaneous SCC and other tumors, and may be a relatively specific marker of malignancy. We studied 20 SCCs, 20 KAs, and an additional 10 regressing KAs (rKA) by immunohistochemistry for the expression of p53 protein. Since p53 is believed to play a pivotal role in the regulation of cell division, we also quantitated proliferation in the tumors by examining Ki-67 antigen expression.

Results:  Sixteen (80%) of the KAs showed nuclear staining with anti-p53 antibody, distributed along the outermost layers of the aggregates of neoplastic cells, while 12 (60%) of the SCCs were p53 positive. Eight (80%) of the rKAs also showed p53 positivity. Mean Ki-67 proliferation fraction was higher for KA than for SCC (55% vs 46%), but this difference was not statistically significant. p53 Expression did not correlate with the grade of SCC.

Conclusions:  A majority of KA, rKA, and SCC contain stainable quantities of p53 protein, supporting the view that KA is a type of regressing SCC.(Arch Dermatol. 1994;130:181-186)

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