PDCD1 and neoplasm: PCSK9 levels were found to be elevated in tumor tissues correlating with poorer prognosis in patients. Reducing PCSK9 expression through pharmacological inhibitors or siRNA could inhibit the cancer cells’ stemness-like characteristics in a LDLR-dependent process. Inhibiting PCSK9 increased the infiltration of CD8+ T cells and enhanced the efficacy of anti-PD-1 immunotherapy against tumors.