PurposeThe aim of this study was to evaluate the combined prognostic value of calf circumference (CC) and serum albumin on mortality in patients with cancer cachexia aged ≥65 years. MethodsThis multicenter cohort study involved 5322 older patients with cancer cachexia from hospitals. The combined indicator of CC and albumin was defined as the calf circumference-albumin index (CCA). Harrell's C index, a time-dependent receiver operating characteristic (ROC) curve analysis, was used to assess the prognostic performance of the CCA and other indices. Optimal threshold was used to determine the cutoff values of CC and albumin, and the association between the CCA and all-cause mortality was assessed using Kaplan-Meier analysis and COX proportional hazard regression models. ResultsThere were 3875 men and 1447 women with a mean age of 72.0 (68.0, 78.0) years and a mean follow-up time of 55.0 (25.0, 85.0) months. A total of 1269 patients were classified into the low CCA group (0 score) by the optimal thresholds method. In the overall population, the CCA showed better differentiating power in predicting mortality in older patients with cancer cachexia compared to CC or albumin alone (C-index = 0.639, 95%CI = 0.612-0.666, P<0.05). The time-dependent ROC showed that the CCA had the highest prognostic value of all the measures studied (P<0.05). In the overall population, male and female patients with the high CCA (2 score) had better performance than those with the low CCA (0 score, 1 score). ConclusionsThe CCA index, combined CC and albumin together, could significantly predict the mortality of older patients with cancer cachexia, which might provide new help for future clinical management.