Depletion of Psoas Muscle Mass after Systemic Chemotherapy Is Associated with Poor Prognosis in Patients with Unresectable Pancreatic Cancer

SIMPLE SUMMARY: The psoas muscle mass index (PMI) is a simplified tool used in the quantification of skeletal muscle. The aim of our study was to investigate whether the PMI at diagnosis or its decrease during chemotherapy can influence the prognosis of unresectable pancreatic cancer. The median overall survival (OS) was 278.0 (95% confidence interval (CI), 199.1–356.9) days in the high-PMI group, and 221.0 (95% CI, 90.9–351.1) days in the low-PMI group (p = 0.329). The median OS was 347.0 (95% CI, 289.1–404.9) days in the group without PMI decrease and 172.0 (95% CI, 129.8–214.2) days in the group with PMI decrease (p = 0.001). We determined that the PMI at diagnosis was not associated with OS in patients with unresectable pancreatic cancer receiving systemic chemotherapy, whereas PMI decrease during chemotherapy influenced the OS. ABSTRACT: The impact of the psoas muscle mass index (PMI) on survival is still poorly understood in unresectable pancreatic cancer. Thus, we aimed to investigate whether the PMI at diagnosis or its decrease during chemotherapy can influence the prognosis of unresectable pancreatic cancer. The data of 100 patients were analyzed, and they were divided into two groups according to the median PMI in each sex. Subsequently, 72 patients undergoing computed tomography (CT) within 30–100 days from CT at diagnosis were evaluated in terms of PMI change rate, and divided into two groups based on the median. We evaluated the clinical characteristics and outcomes in terms of the PMI at diagnosis or its decrease during chemotherapy. The median PMI was 5.00 in males, and 3.66 in females. The median overall survival (OS) was 278.0 days in the high-PMI group and 221.0 days in the low-PMI group (p = 0.329). The median PMI change rate was −2.4%. The median OS was 347.0 days in the group without PMI decrease and 172.0 days in the group with PMI decrease (p = 0.001). We determined that a pivotal prognostic factor was not the PMI at diagnosis, but rather PMI decrease during chemotherapy in unresectable pancreatic cancer.