Our study fills an important knowledge gap in metastatic breast cancer in two main regards: (i) the immune phenotype and PD-1/LAG-3 expression within metastatic breast cancer are significantly different from the primary tumor and among anatomical metastatic sites and (ii) PD-1+/LAG-3+ expression is strongly associated with a “hot” immune phenotype. Here, PDCD1 is linked to breast cancer.