PDCD1 and neoplasm: Recent studies have divided solid tumors into two subtypes: “hot” tumor and “cold” tumor.38,39 The latter, with less TILs, usually represented poor response to immunotherapy,40 which was a major obstacle to effective treatment with anti-PD-1 among CRC patients.41,42 And researchers tried to develop strategies to turn “cold” tumors into “hot” tumors these days.