PDCD1 and neoplasm: In addition, a KD can enhance the efficacy of anti- programmed cell death 1 (PD-1) immunotherapy in animal models of RET melanoma, renal cell carcinoma, and lung cancer [26] and anti- cytotoxic T lymphocyte-associated protein-4 (CTLA-4) immunotherapy in breast and colon cancer cells and improved overall survival in mouse tumor models [177].