PDCD1 and breast cancer: At present, studies have validated the specific antitumor function of CD39+CD8+ T cells in non-small cell lung cancer (NSCLC) tumor tissues, which confirmed that CD39+CD8+ T cells could be the predictor of prognosis in patients with NSCLC after anti-PD-1/PD-L1 therapy (41) and defined the protective prognostic role of CD39high tissue memory CD8+ T cells in luminal-like breast cancer (42).