Early prediction by 18F-FDG PET/CT for progression-free survival and overall survival in patients with metastatic colorectal cancer receiving third-line cetuximab-based therapy

OBJECTIVE: In metastatic colorectal cancer (mCRC) with wild-type K-ras, cetuximab-based regimen is an option for third-line therapy. The objective of this study was to assess if early response evaluation by ¹⁸F-FDG PET/CT can predict progression-free survival (PFS) and overall survival (OS) in these patients. PATIENTS AND METHODS: Patients with mCRC going to receive third-line cetuximab-based therapy were enrolled. F-FDG PET/CT studies were arranged at baseline and at the ends of the first and fourth weeks of therapy. Treatment response was evaluated with 2 methods: method 1 based on PET response criteria in solid tumors 1.0 and method 2 based on the assumption that an increase in peak tumor metabolism implies nonresponse. Progression-free survival was counted to tumor progression based on the Response Evaluation Criteria in Solid Tumors 1.1 or death. The predictive powers for PFS and OS were analyzed using the Kaplan-Meier method and the log-rank test. RESULTS: Twenty-seven patients were eligible with a median PFS of 5.8 months and a median OS of 9.1 months. Method 2 predicts PFS (P = 0.001) and OS (P < 0.001) at the end of the first week, whereas method 1 does not. Both methods predict PFS and OS at the end of the fourth week. CONCLUSIONS: Early response evaluation by F-FDG PET/CT predicts PFS and OS in patients with mCRC receiving third-line cetuximab-based therapy. Early therapeutic change may be possible for nonresponsive patients after 1 week of treatment.