PDCD1 and cancer: To date, not only anti-PD-1 antibodies (e.g., nivolumab and pembrolizumab) but also anti-PD-L1 (e.g., atezolizumab, avelumab, and durvalumab) and anti-CTLA-4 (e.g., ipilimumab) antibodies have been approved worldwide as therapeutic medicines for multiple cancer types [18–23].