Since we previously reported that circulating regulatory T (Treg) cells represent a promising potential dynamic biomarker to predict efficacy after immunotherapy in patients with NSCLC (Kang et al. 2022), we analyzed the immune cell populations, including Treg cells, soluble PD-1, and soluble PD-L1 levels between the low GDF15 group and high GDF15 group in patients with lung cancer (Table 2). Here, GDF15 is linked to lung cancer.