Skeletal muscle wasting is considered the central feature of cachexia, but the potential for skeletal muscle anabolism in patients with advanced cancer is unproven. Objective: We investigated the clinical course of skeletal muscle wasting in advanced cancer and the window of possible muscle anabolism. Design: We conducted a quantitative analysis of computed tomography (CT) images for the loss and gain of muscle in populationbased cohorts of advanced cancer patients (lung, colorectal, and

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... s cancer and cholangiocarcinoma) in a longitudinal observational study. Results: Advanced-cancer patients (n = 368; median survival: 196 d) had a total of 1279 CT images over the course of their disease. With consideration of all time points, muscle loss occurred in 39% of intervals between any 2 scans. However, the overall frequency of muscle gain was 15.4%, and muscle was stable in 45.6% of intervals between any 2 scans, which made the maintenance or gain of muscle the predominant behavior. Multinomial logistic regression revealed that being within 90 d (compared with .90 d) from death was the principal risk factor for muscle loss (OR: 2.67; 95% CI: 1.45, 4.94; P = 0.002), and muscle gain was correspondingly less likely (OR: 0.37; 95% CI: 0.20, 0.69; P = 0.002) at this time. Sex, age, BMI, and tumor group were not significant predictors of muscle loss or gain. Conclusions: A window of anabolic potential exists at defined early phases of the disease trajectory (.90 d survival), creating an opportunity for nutritional intervention to stop or reverse cachexia. Cancer patients within 90 d of death have a low likelihood of anabolic potential. Am J Clin Nutr