Tumor-Associated Macrophages in Merkel Cell Carcinoma: Old Balances, New Checks

A recent report sheds light on the tumor-associated macrophages (TAM) in Merkel cell carcinoma (MCC), and the association of S100A8-expressing TAMs with resistance to anti-PD-(L)1 inhibitors. These data improve our understanding about why some tumors with brisk tumor-infiltrating lymphocytes do not respond to immunotherapy and provide a compelling rationale to target myeloid checkpoints in MCC. See related article by Tabachnick-Cherny et al., p. 1189