TTF1 and melanoma: A combination of CK20 which is highly sensitive for MCCs, together with thyroid transcription factor-1 (TTF-1) and CK7 which are expressed in SCLCs but consistently absent in MCCs as well as HBM45, NKI/C3, and S-100 markers, which are positive in melanoma but negative in MCCs, can be used to identify MCCs [24, 51–53].