MSH6 and Merkel cell skin cancer: In the present study, we investigated whether mismatch repair (MMR) protein deficiency also occurred in Merkel cell carcinoma cases at our center or not with immunohistochemical staining for MMR proteins (MLH1, PMS2 [postmeiotic segregation increased 2], MSH2 [mutS homolog 2], and MSH6 [mutS homolog 6]) expression.