GDF15 and neoplasm: Since PD-L1 expression in tumor tissues, such as soluble PD-1 and PD-L1, was also not significantly related to plasma GDF15 levels, these results suggest an important association between PD-1+ CD8+ T cells and PD-1+ Treg cells and plasma GDF15 levels in advanced NSCLC patients treated with PD-1/PD-L1 inhibitors.