Comparison of EORTC criteria and PERCIST for PET/CT response evaluation of patients with metastatic colorectal cancer treated with irinotecan and cetuximab.

The study aim was to compare European Organization for Research and Treatment of Cancer (EORTC) criteria with PET Response Criteria in Solid Tumors (PERCIST) for response evaluation of patients with metastatic colorectal cancer treated with a combination of the chemotherapeutic drug irinotecan and the monoclonal antibody cetuximab. From 2006 to 2009, patients with metastatic colorectal cancer were prospectively included in a phase II trial evaluating the combination of irinotecan and cetuximab every second week, as third-line treatment. (18)F-FDG PET/CT was performed between 1 and 14 d before the first treatment and after every fourth treatment cycle until progression was identified by CT with Response Evaluation Criteria in Solid Tumors (RECIST). Response evaluation with (18)F-FDG PET/CT was retrospectively performed according to both EORTC criteria and PERCIST, classifying the patients into 4 response categories: complete metabolic response (CMR), partial metabolic response (PMR), stable metabolic disease (SMD), and progressive metabolic disease (PMD). Individual best overall metabolic response (BOmR) was registered with both sets of criteria, as well as survival within response categories, and compared. A total of 61 patients and 203 PET/CT scans were eligible for response evaluation. With EORTC criteria, 38 had PMR, 16 had SMD, and 7 had PMD as their BOmR. With PERCIST, 34 had PMR, 20 had SMD, and 7 had PMD as their BOmR. None of the patients had CMR. There was agreement between EORTC criteria and PERCIST in 87% of the patients, and the corresponding κ-coefficient was 0.76. Disagreements were confined to PMR and SMD. Median overall survival (OS) in months with EORTC criteria was 14.2 in the PMR group and 7.2 in the combined SMD + PMD group. With PERCIST, it was 14.5 in the PMR group and 7.9 in the SMD + PMD group. Response evaluation with EORTC criteria and PERCIST gave similar responses and OS outcomes with good agreement on BOmR (κ-coefficient, 0.76) and similar significant differences in median OS between response groups. Compared with EORTC criteria, we find PERCIST unambiguous because of clear definitions and therefore more straightforward to use.