Defining Low Muscle Mass in Cancer Patients: Sex-Specific Computed Tomography-Derived Cutoff Values and Survival Impact-A Multicenter Cohort Study.

Abstract

Low skeletal muscle mass is associated with adverse cancer outcomes and is a key diagnostic criterion for malnutrition in the Global Leadership Initiative on Malnutrition, emphasizing the importance of muscle mass assessment. This study aimed to establish sex-specific cutoff values for skeletal/psoas muscle mass index (SMI/PMI), calculated from computed tomography, in cancer patients for predicting prognosis. In this multicenter cohort study, preoperative SMI and PMI were analyzed in patients with gastric cancer who underwent gastrectomy without preoperative therapy between 2011 and 2016. Using 80% of the cases as a training set, sex-specific cutoffs for overall survival (OS) were determined via the optimal stratification method, adjusted for age and stage. The remaining 20% were used to validate OS differences between high and low muscle-mass groups. Of 3841 registered patients from 17 hospitals, 3797 were analyzed. Spline plots showed a strong association between lower muscle mass and worse OS in males, but a weaker association in females. The SMI cutoffs were 40 cm²/m² (males) and 31 cm²/m² (females); PMI cutoffs were 3.7 cm²/m² (males) and 2.9 cm²/m² (females). In the validation set, low SMI and PMI were significantly associated with poor OS in males. In females, only PMI remained significant; body mass index better stratified prognosis than muscle indices. The proposed cutoffs may facilitate the early identification of muscle loss or malnutrition, supporting timely intervention. The observed sex differences highlight the necessity to develop sex-specific strategies for nutritional and muscle mass management during cancer treatment.