P63 expression in merkel cell carcinoma predicts poorer survival yet may have limited clinical utility

Objectives: To determine the clinical utility of p63 expression, which has been identified in several cohorts as a predictor of poorer prognosis in Merkel cell carcinoma (MCC). Methods: Immunohistochemistry was used to determine p63 expression on MCC tumors from 128 patients. Results: Of the patients, 33% had detectable p63 expression. p63 Positivity was associated with an increased risk of death from MCC (hazard ratio, 2.05; P = .02) in a multivariate Cox regression model considering stage at presentation, age at diagnosis, and sex. Although p63 expression correlated with diminished survival in this largest cohort reported thus far, the effect was weaker than that observed in prior studies. Indeed, within a given stage, p63 status did not predict survival in a clinically or statistically significant manner. Conclusions: It remains unclear whether this test should be integrated into routine MCC patient management.