Combined Metabolically Active Tumor Volume and Early Metabolic Response Improve Outcome Prediction in Metastatic Colorectal Cancer

Stratification of metastatic colorectal cancer (mCRC) patients is mostly based on clinical and biological characteristics. This study aimed to validate the prognostic value of ¹⁸F-FDG PET/CT-based biomarkers such as baseline whole-body metabolically active tumor volume (WB-MATV) and early metabolic response (mR) in mCRC. Methods: The development cohort included chemorefractory mCRC patients enrolled in two prospective Belgian multicenter trials evaluating last-line treatments (multikinase inhibitors). The validation cohort included mCRC patients from an Italian center treated with chemotherapy and bevacizumab as first-line. Baseline WB-MATV was defined as the sum of metabolically active volumes of all target lesions identified on the baseline ¹⁸F-FDG PET/CT. Early metabolic response (mR) assessment was performed following usual response criteria (PERCIST-30%, PERCIST-15%, EORTC) and the so-called CONSIST method, which defines response as a decrease of SULmax ≥ 15% for all target lesions. Baseline WB-MATV and early mR assessment were investigated along with usual clinical factors and correlated with overall and progression-free survival (OS/PFS). Results: Clinical factors, baseline WB-MATV and early mR were evaluable in 192/239 and 94/125 patients of the development and validation cohorts, respectively. Except for PERCIST-30%, all response methods were equivalent in terms of outcome prediction and CONSIST was found to be the most accurate. Baseline WB-MATV and early mR using CONSIST method were independent prognostic parameters after adjustment for clinical factors in the development and validation sets for both OS (HR WB-MATV: 1.87 (1.17-2.97), P = 0.005, and HR early mR: 1.79 (1.08-2.95), P = 0.02 for the validation set), and PFS (HR WB-MATV: 1.94 (1.27-2.97), P = 0.002, and HR early mR: 1.69 (1.04-2.73), P = 0.03 for the validation set). Conclusion: Baseline WB-MATV and early mR are strong independent prognostic biomarkers for OS/PFS in mCRC, regardless of treatment received. Therefore, combining these biomarkers improves risk stratification for OS/PFS in mCRC.