CD99 and Merkel cell skin cancer: Additionally, MCC is typically negative for thyroid transcription factor 1 (TTF-1), leukocyte common antigen/cluster of differentiation 45 (LCA/CD45), other lymphocytic/lymphoblastic markers (CD20, CD3, and TdT), S100, SOX10, other melanocytic markers (Melan A/Mart-1, HMB45), vimentin, CK7, CD99, and sal-like protein 4 (SALL4) [92,93,94,95,96,97,98].