Although the preliminary trials on PD‐1, PD‐L1, and CTLA‐4 immunotherapy displayed encouraging outcomes with SCLC patients, it seems that the clinical efficacy of immunotherapy for SCLC was far less pronounced than that for solid tumors, such as NSCLC and melanoma (Nagai & Muto, 2018). Here, CTLA4 is linked to melanoma.