IDO1 and neoplasm: Along with the observations that cytotoxic T-lymphocyte antigen 4 (CTLA4), programmed cell death ligand-1 (PD-L1), and indolamine 2,3-dioxygenase 1 (IDO1) expression levels were upregulated in signature 3 tumors and that BRCA-mutated BCs showed increased tumor infiltrating lymphocytes (TILs) compared with BRCA wild-type, these data suggest the potential of using immune checkpoint inhibitors in BRCA-signature tumors16,17.