Background: Handgrip strength (HGS) and platelet-to-albumin ratio (PAR) are established prognostic markers of cancer cachexia. This study evaluates the combined efficacy of HGS and PAR using a single index (HPA) for predicting survival outcomes in cancer patients with cachexia aged >= 18 years. Methods: The multicenter Nutrition Status and Its Clinical Outcomes in Common Cancers study, conducted from July 2013 to April 2022, enrolled 5189 participants. Thresholds for HGS and PAR were determined using optimal stratification, leading to the development of HPA index. Prognostic accuracy was assessed using time-dependent receiver operating characteristic analysis, Kaplan-Meier survival curves, and Cox proportional hazards models. Results: The cohort consisted of 3127 men and 2062 women, with a median follow-up of 36 months, and mean age of 58 years. Low HGS thresholds were 19 kg (female) and 31.9 kg (male), and high PAR cut-offs were 9.07 x 10(9) (female) and 6.52 x 10(9) (male). Both low HGS and high PAR levels were linked to increased mortality risk. The HPA index showed superior prognostic accuracy (C-index = 0.611; 95% confidence interval: 0.58-0.61; P < 0.001) compared with HGS or PAR alone. Kaplan-Meier analysis indicated significantly reduced survival in patients with low HGS and high PAR. Conclusions: The HPA index is a clinically significant prognostic tool for cancer cachexia, enhancing survival prediction and guiding patient management. (c) 2025 Elsevier Inc. All rights are reserved, including those for text and data mining, AI training, and similar technologies.