Background: Sarcopenia negatively impacts survival outcomes, treatment tolerability and functionality in cancer patients. However, there is a limited appreciation of its true prevalence, due inconsistent diagnostic methods and limited oncologist training. Methods: 29 French healthcare establishments participated in this cross-sectional study, recruiting patients with those metastatic cancers most frequently encountered in routine practice (colon, breast, kidney, lung, prostate). The primary

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... ome was low muscle mass prevalence, as diagnosed by estimating the skeletal mass index (SMI) at the third-lumbar vertebrae (L3) level via computed tomography (CT). Other objectives included an evaluation of nutritional management, physical activity, and toxicities related to ongoing treatment.Results: 766 patients (49.9% males) were enrolled with a mean age of 65.0 years. Low muscle mass prevalence was 69.1%. Cachexia prevalence among patients was 44.5%, but only one-third of sarcopenic patients benefited from nutritional support. Physicians highly underdiagnosed those patients identified with low muscle mass, as defined by the primary objective, by 74.3% and 44.9% in obese and non-obese patients, respectively. Multivariate analyses revealed a lower risk of low muscle mass for females (OR: 0.22, P<0.01) and those without brain metastasis (OR: 0.34, P<0.01). Low muscle mass patients were more likely to have delayed treatment administration due to toxicity (11.9% versus 6.8%, P=0.04). Conclusions: There is a critical need to raise awareness of low muscle mass diagnosis among oncologists, and for improvements in nutritional management and physical therapies of cancer patients to curb potential sarcopenia. This calls for cross-disciplinary collaborations among oncologists, nutritionists and physiotherapists.