Standardized Added Metabolic Activity Predicts Survival After Intra-arterial Resin-Based 90Y Radioembolization Therapy in Unresectable Chemorefractory Metastatic Colorectal Cancer to the Liver.

Purpose: Standardized added metabolic (SAM) activity is a functional objective measurement of the total tumoral metabolic activity that avoids partial volume effect and thresholding, which limit conventional PET parameters. The purpose of this study is to investigate the role of SAM in predicting survival in unresectable, chemorefractory colorectal hepatic metastatic disease treated with resin-based Y-90 radioembolization. Materials and Methods: This is a prospective correlative study of patients with unresectable, chemorefractory colorectal liver metastasis who underwent F-18-FDG PET/CT and CT/MRI before and after Y-90. Target RECIST, PERCIST, change in total glycolytic activity (Delta TGA), and Delta SAM treatment response were assessed. Percentage changes in diameter, SUVpeak, TGA, and SAM were calculated pre- and post-Y-90 therapy and objective response was defined as >30% change (responders). Survival analysis by Kaplan-Meier, log-rank, and Cox proportional hazard models were performed and significance was set at <0.05. Results: Sixteen patients (mean age of 61.6) were enrolled and performed a total of 20 Y-90 therapies. After Y-90, target Delta SAM showed an objective response rate of 40% vs. 35%, 30%, and 22.2% based on target Delta TGA, PERCIST, and RECIST criteria, respectively. Median overall survival (OS) of the cohort after Y-90 was 9.2 months (CI 95% 2.2-16.2). Patients demonstrating objective response based on Delta SAM had a median OS of 22.7 months (CI 95% 12.4-33.0) vs. 6.7 (CI 95% 4.2-9.2) in non-responders (P = 0.007). On multivariate analysis, hazard ratios for the objective response group based on target Delta SAM were 0.01 (P = 0.03) vs. 0.05 (P = 0.08), 0.20 (P = 0.29), and 0.91 (P = 0.98) based on target Delta TGA, PERCIST, and RECIST criteria, respectively. Conclusions: In unresectable colorectal liver metastatic disease refractory to standard chemotherapy,Delta SAM predicted OS for assessment of response following Y-90 radioembolization therapy, whereas RECIST, PERCIST, and Delta TGA did not.