Psoas mass index at the level of the third lumbar vertebra on computed tomography is a prognostic predictor for metastatic castration-sensitive prostate cancer

Abstract Background Computed tomography-defined low skeletal muscle mass is associated with oncological outcomes in prostate cancer. However, its association with the outcomes in hormone-treated metastatic castration-sensitive prostate cancer is unclear. This study aimed to determine the association between metastatic castration-sensitive prostate cancer and psoas muscle parameters. Methods We retrospectively reviewed 121 patients with N1 and/or M1 metastatic castration-sensitive prostate cancer who underwent primary androgen deprivation therapy either with a luteinizing hormone-releasing hormone agonist/antagonist or with surgical castration accompanied by first-generation anti-androgen bicalutamide treatment between 2005 and 2021. Before treatment, the psoas muscle index at the level of the third lumbar vertebra (psoas muscle area [cm2]/height2 [m2]) and the mean Hounsfield units of the psoas muscle were evaluated in relation to oncological outcomes using non-contrast computed tomography. Results The median follow-up was of 56.9 months. Furthermore, 82 (67.7%) and 53 (43.8%) patients progressed to castration-resistant prostate cancer and died during follow-up, respectively. Multivariate analysis of castration-resistant prostate cancer-free survival and overall survival showed significant differences in the Gleason score, clinical N stage, and psoas muscle index (median cut-off: 3.044 cm2/m2). Kaplan–Meier curves of a novel prognostic model using these three risk factors showed significant differences (P <0.001). Conclusions A pretreatment low psoas muscle index was an independent predictor of a poor castration-resistant prostate cancer-free survival and overall survival in patients with N1 and/or M1 metastatic castration-sensitive prostate cancer. Our novel prognostic model could help predict worse outcomes in susceptible patients.