In patients with metastatic solid tumors including relapsed SCLC, targeting other immune checkpoints, such as PD-1 and CTLA-4, with immunotherapies, including TIM3 and LAG3, are being evaluated in clinical trials in combination with anti-PD-1 or anti-PD-L1 antibodies (NCT03708328, NCT03365791). Here, PDCD1 is linked to small cell lung carcinoma.