Purpose: In advanced cancer, oncological treatment is influenced by performance status (PS); however, this has limitations. Biomarkers of systemic inflammation may have prognostic value in advanced cancer. The study compares key factors in prognosis (performance status, patient-reported outcomes; PRO) with an inflammation-based score (Glasgow Prognostic Score, mGPS). A new method of prognosis in advanced cancer (combining performance status and mGPS) is tested and then validated. Experimental Design: Two international biobanks of patients with advanced cancer were analyzed. Key prognostic factors [performance status, PROs (European Organisation for Research and Treatment of Cancer Quality of Life Questionnaire C-30), and mGPS (using C-reactive protein and albumin concentrations)] were examined. The relationship between these and survival was examined using Kaplan-Meier and Cox regression methods, in a test sample before independent validation. Results: Data were available on 1,825 patients (test) and 631 patients (validation). Median survival ranged from 3.2 months (test) to 7.03 months (validation). On multivariate analysis, performance status (HR 1.62-2.77) and mGPS (HR 1.51-2.27) were independently associated with, and were the strongest predictors of survival (P < 0.01). Survival at 3 months varied from 82% (mGPS 0) to 39% (mGPS 2) and from 75% (performance status 0-1) to 14% (performance status 4). When used together, survival ranged from 88% (mGPS 0, PS 0-1) to 10% (mGPS 2, performance status 4), P < 0.001. Conclusion: A systemic inflammation-based score, mGPS, and performance status predict survival in advanced cancer. The mGPS is similar to performance status in terms of prognostic power. Used together, performance status and mGPS act synergistically improving prognostic accuracy. This new method may be of considerable value in the management of patients with advanced cancer.