INSM1 and Merkel cell skin cancer: The strengths of our study are the following: (1) the comparison of well-established IHC markers (CKAE1/AE3, CK20, synaptophysin, chromogranin A, and NF) with recently available new antibodies (SATB2 and INSM1) for MCC metastasis identification; (2) the high number of evaluated cases; (3) providing assessment intertumoral heterogeneity in multiple metastases; (4) emphasis on the practical aspects by implementing a user-friendly, semiquantitative, reproducible scoring system that pathologists could apply in routine diagnostics.