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

[BACKGROUND] 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.

[METHODS] 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.

[RESULTS] 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 cm/m (males) and 31 cm/m (females); PMI cutoffs were 3.7 cm/m (males) and 2.9 cm/m (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.

[CONCLUSIONS] 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.