Pet/Ct in the Evaluation of Response to Treatment with Bevacizumab and Chemotherapy in Patients with Advanced Colorectal Cancer

Background: Bevacizumab has efficacy in first-line treatment of advanced colorectal cancer. The overall response with Bevacizumab is low in some studies. Not know the ideal method of assessing response to therapy with bevacizumab. Metabolic imaging of tumor viability with 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET), and simultaneous anatomic localization provided by low-dose non-enhanced computed tomography (CT), can be obtained in a combined modality FDG-PET/CT scan. The purpose of this study was to evaluate the possible contribution of FDG-PET/ CT as a surrogate marker to evaluate treatment response in patients with metastatic colorectal cancer (mCRC) who had been treated with bevacizumab and standard chemotherapy. Methods: Retrospective analysis of 28 patients with advanced colorectal cancer who had been treated in the Hospital Universitario Virgen de las Nieves in Granada. Analyses included all patients who initiated bevacizumab in combination with either first-line oxaliplatin or irinotecan based regimens. FDG-PET/CT scans were performed before the start of the treatment and after six cycles of therapy. Results were compared to concurrent contrast-enhanced CT. Response to treatment was determined according to RECIST size criteria obtained from data from thin (3-5mm) slice CT, and changes in uptake of 18F-FDG uptake on PET. Results: A total of 28 patients were evaluated. Overall, 22 patients had favorable response to treatment, and only 6 had progression of disease. Complete response (CR) was evident on FDG-PET in 6/28 (21,4%) patients whereas only 5 were deemed CR by CT and partial response (PR) in 15/28 (64,3%) with both techniques. Similarly, only 1/ 28 (3,6%) lesion appeared stable by FDG-PET and CT criteria. Progression of disease (PT) was evident on FDG-PET in 6/28 (21,4%) patients whereas only 5 were deemed PT by CT. There was a strong correlation between metabolic response (changes in SUV) and objective response (r = 0.81, P