Early post-treatment FDG PET predicts survival after 90Y microsphere radioembolization in liver-dominant metastatic colorectal cancer

The aim of this study was to evaluate the predictive value of early metabolic response 4 weeks post-treatment using F-18-fluorodeoxyglucose (FDG) positron emission tomography (PET)/CT in patients with unresectable hepatic metastases of colorectal cancer (CRC) undergoing radioembolization (RE) with Y-90-labelled microspheres. A total of 51 consecutive patients with liver-dominant metastases of CRC were treated with RE and underwent F-18-FDG PET/CT at baseline and 4 weeks after RE. In each patient, three hepatic metastases with the highest maximum standardized uptake value (SUVmax) were selected as target lesions. Metabolic response was defined as > 50 % reduction of tumour to liver ratios. Survival analyses using Kaplan-Meier and multivariate analyses were performed to identify prognostic factors for overall survival (OS). Investigated baseline characteristics included age (> 60 years), performance status (Eastern Cooperative Oncology Group > 1), bilirubin (> 1.0 mg/dl), hepatic tumour burden (> 25 %) and presence of extrahepatic disease. The median OS after RE was 7 months [95 % confidence interval (CI) 5-8]; early metabolic responders (n = 33) survived longer than non-responders (p < 0.001) with a median OS of 10 months (95 % CI 3-16) versus 4 months (95 % CI 2-6). Hepatic tumour burden also had significant impact on treatment outcome (p < 0.001) with a median OS of 5 months (95 % CI, 3-7) for patients with > 25 % metastatic liver replacement vs 14 months (95 % CI 6-22) for the less advanced patients. Both factors (early metabolic response and low hepatic tumour burden) remained as independent predictors of improved survival on multivariate analysis. These are the first findings to show that molecular response assessment in CRC using F-18-FDG PET/CT appears feasible as early as 4 weeks post-RE, allowing risk stratification and potentially facilitating early response-adapted treatment strategies.