Limitations of the dose-escalation part of this phase 1 study are: 60% of patients had received ≥3 lines of systemic therapy before enrollment; there were a variety of tumor types; and most patients had tumors that were not expected to have strong responses to anti-PD-1 monotherapy, including colorectal, pancreatic, ovarian, prostate, and breast cancers (23–27). This evidence concerns the gene PDCD1 and breast cancer.