INSM1 and Merkel cell skin cancer: However, only upon targeted deletion of TP53 did the mice develop skin tumors with classic MCC histopathology, localized to the dermis without clear connection to the epidermis or hair follicles, and with characteristic immunophenotypic features, including dot-like expression of KRT8, SOX2, ISL1, insulinoma-associated protein 1 (INSM1), and POU3F2 [46].