Prognostic Impact of Ectopic Fat Deposition within Psoas Muscle in Stage IV Gastric Cancer Patients Undergoing Systemic Chemotherapy

Aims: In this study, we focused on the fat ratio within psoas muscle (FRPM) and sought to clarify the impact of FRPM on overall survival (OS) in stage IV gastric cancer (GC) patients undergoing systemic chemotherapy (n = 79, median age = 69 years, 59 males). Methods: The median FRPM was 1.67 %. Forty patients with FRPM ≥1.67 % were defined as the FRPM-high group, and the remaining 39 patients was defined as the FRPM-low group. The median PMI in male and female patients was 4.35 cm(2)/m(2) and 2.88 cm(2)/m(2). Thirty male patients with PMI ≥4.35 cm(2)/m(2) and 10 female patients with PMI ≥2.88 cm(2)/m(2) was defined as the PMI-high group, and the remaining 39 patients was defined as the PMI-low group. Results: The 1-, 2- and 3- year cumulative OS rate for all cases was 70.8%, 24.3% and 14.6%. The proportion of ECOG-PS 2 or 3 in patients with FRPM-high and FRPM-low was 17.5% (7/40) and 2.6% (1/39). The 1-, 2- and 3- year cumulative OS rate in patients with FRPM-high and FRPM-low was 67.3%, 14.3% and 7.6% in the FRPM-high group and 74.8%, 40.5% and 32.4% in the FRPM-low group (P = 0.0341). The 1-, 2- and 3- year cumulative OS rate in patients with PMI-high and PMI-low was 86.7%, 40.4% and 30.0% in the PMI-high group and 55.8%, 12.8% and 6.4% in the PMI-low group (P < 0.0001). In the multivariate analysis of factors associated with OS, PMI (P = 0.0047) and FRPM (P = 0.0019) were independent predictors for the OS. Conclusion: Higher FRPM can be associated with decreased physical activity, and not only skeletal muscle mass but also skeletal muscle function can be an essential prognostic factor in stage IV GC patients undergoing systemic chemotherapy.