p53 oncoprotein expression and proliferation index in keratoacanthoma and squamous cell carcinoma.
METHODS
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 20SCCs, 20KAs, 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.
Kerschmann
R L
RL
Department of Pathology, University of California at San Francisco.
McCalmont
T H
TH
LeBoit
P E
PE
D002294:Carcinoma, Squamous Cell / Q000235:genetics / Q000378:metabolism*; D002455:Cell Division; D016158:Genes, p53; D006801:Humans; D007150:Immunohistochemistry; D015603:Keratinocytes / Q000378:metabolism; D007636:Keratoacanthoma / Q000235:genetics / Q000378:metabolism*; D019394:Ki-67 Antigen; D009363:Neoplasm Proteins / Q000302:isolation & purification; D009687:Nuclear Proteins / Q000302:isolation & purification; D012878:Skin Neoplasms / Q000235:genetics / Q000378:metabolism*
D019394:Ki-67 Antigen; D009363:Neoplasm Proteins; D009687:Nuclear Proteins