Development and validation of a grading system for assessing muscle mass phenotype using mid‐upper arm muscle area and handgrip strength in patients with incurable cancer

Abstract Background This study aimed to develop and validate a distinct method to evaluate muscle mass phenotype in patients with incurable cancer based on a combination of mid‐upper arm muscle area (MUAMA) and handgrip strength (HGS). Methods This prospective cohort study was conducted with patients with incurable cancer who were enrolled at the palliative care unit of a cancer institute. The 1,660 patients were randomized into two data sets: training (70%; n = 1162), used to determine the muscle mass phenotype groups, derived from a combination of MUAMA and HGS cutoff points related to 180‐days mortality; and validation (30%; n = 498), used to evaluate the relationship of the proposed muscle phenotype grading system with performance status, body composition, nutrition status, and mortality. Results The training data set resulted in three distinct groups formed by combining the cutoff points of MUAMA and HGS, with the best muscle mass phenotype being group 1, the group with any impairment of muscle mass being the 2, and the worst muscle mass phenotype being group 3. In the validation data set, lower performance status (both sexes p < 0.001), worse skeletal muscle index (both sexes p < 0.001), muscle radiodensity (men, p = 0.001; women, p = 0.008), and nutritional status (men, p = 0.003; women, p < 0.001) were observed as MUAMA and HGS values diminished. Patients in group 3 presented significantly higher risk of 180‐day mortality (both sexes p < 0.001). Conclusion The muscle mass phenotype grading system proved to be able to identify patients with lower performance status, worse body composition measurements and nutritional status, and higher risk of death in 180 days.