High Expression of the Mismatch Repair Protein MSH6 Is Associated With Poor Patient Survival in Melanoma.

OBJECTIVES: The outcome of patients with primary melanoma (PM) cannot be completely explained based on currently adopted clinical-histopathologic criteria. In this study, we evaluated the potential prognostic value of mismatch repair protein expression in PMs. METHODS: We examined the immunohistochemical staining of mismatch repair proteins in 18 benign nevi and 101 stage I to III PMs and investigated their association with tumor clinicopathologic variables and melanoma mortality. RESULTS: Expression of MSH2, MLH1, and PMS2 was high in benign nevi and reduced in a subset of PMs. Conversely, MSH6 expression was absent or extremely low in benign nevi and increased in a subset of PMs. In the multivariate analysis, including sex, age, Breslow thickness, and ulceration, high MSH6 expression in PMs (ie, immunostaining in >20% of tumor cells) was significantly associated with an increased risk of melanoma mortality (relative risk, 3.76; 95% confidence interval, 1.12-12.70). CONCLUSIONS: MSH6 protein expression can be a valuable marker to improve prognosis assessment in PMs.