Association between skeletal muscle loss and the response to nivolumab immunotherapy in advanced gastric cancer patients.

BACKGROUND Skeletal muscle loss is a hallmark of malignancies, including advanced gastric cancer (GC). Although programmed death (PD)-1 inhibitors, including nivolumab, have promising anti-cancer effects, there is limited information regarding markers that can predict these therapeutic effects, which include PD-ligand 1 (PD-L1) expression and the tumor mutation burden. Therefore, we evaluated whether the baseline psoas muscle mass index (PMI, a surrogate for skeletal muscle mass) could predict the response of GC to nivolumab treatment, based on progression-free survival (PFS), the objective response rate, and the disease control rate. METHODS This retrospective study evaluated 31 Japanese patients who received nivolumab for advanced GC and underwent imaging analysis between November 2017 and November 2019. The computed tomography results were used to estimate the psoas major muscle mass. Sex-specific cut-off values were used for the PMI, with low PMI values defined as < 3.6 cm2/m2 for male patients and < 2.9 cm2/m2 for female patients. RESULTS The median PFS interval was 2.3 months for the patients with stage IV GC. Nine patients (29%) had a low baseline PMI, and these patients had significantly shorter median PFS than the group with a non-low baseline PMI (0.5 months vs. 2.4 months, P = 0.004). CONCLUSIONS As a surrogate marker for skeletal muscle loss, the PMI may be useful for predicting the response to nivolumab among patients with advanced GC.