PTGDS and neoplasm: Even though the risk models for the tumor microenvironment, immune cell infiltration, and energy metabolism of LUAD have been reported (37–39), we constructed a 9-gene prognostic risk model based on CYP4B1, KLF4, DPEP2, PTGDS, CYP27A1, ACSS3, HSD17B13, HPGDS, and FA2H, which was validated by an external dataset.