PDCD1 and neoplasm: The non-cumulative probability ranking results suggest that PD-1 + Chemo ranks highest in terms of efficacy, which may be related to the immune microenvironment of SCLC, where PD-L1 inhibitors can only inhibit the binding of PD-1 to PD-L1, and the tumor cells may evade the anti-tumor immune response through the binding of PD-L2 and PD-1 (23, 24).