As inhibition of LSD1 stimulates antitumor immunity and enhances antitumor efficacy of PD-1/PD-L1 blockers in breast cancer and melanoma [21, 22], and PD-L1 is an effective target of immunotherapy that can inhibit T-cell activation by binding PD-1 [39–41], we conjectured that LSD1 may be mainly involved in the development of GC by inhibiting the activation and proliferation of T cells through PD-L1. Here, PDCD1 is linked to breast cancer.