PDCD1 and neoplasm: The use of checkpoint inhibitors (CPIs) targeting T cell co-inhibitory receptors like cytotoxic T lymphocyte associated protein 4 (CTLA-4) or programmed death protein 1 (PD-1), induced strong and durable anti-tumoral responses in several tumor types and improved clinical outcomes for patients with a wide range of cancers; however, a substantial proportion of patients remain unresponsive to CPIs, so a significant unmet need remains [2].