APM, antigen processing machinery; BRCA, Breast Cancer gene; FDR, false‐discovery rate; HER2, human epidermal growth factor receptor‐2; IDO1, indoleamine 2,3‐dioxygenase‐1; PD‐1, programmed death‐1; PD‐L1, programmed death‐ligand‐1; PD‐L2, programmed death‐ligand‐2; PGR, progesterone receptor; SD, standard deviation; TIGIT, T‐cell immunoreceptor with immunoglobulin and immunoreceptor tyrosine‐based inhibition motif domains; TIS, tumor inflammation signature. Here, IDO1 is linked to breast cancer.