PDCD1 and cancer: Over the past decades, inhibition on immune brakes effects of cytotoxic T lymphocyte-associated protein 4 (CTLA-4) and the programmed cell death protein 1 (PD-1) by using immune checkpoint inhibitors (ICIs) have revolutionized the therapeutic strategies of cancer treatment, and become routine part of care for more than 20 different indications, including solid tumors and hematological malignancies (Schoenfeld and Hellmann, 2020).