Impact of third-line treatment with irinotecan plus cetuximab on non-tumor standardized uptake values in patients with metastatic colorectal cancer.

The correct interpretation of metabolic response in cancer cells to therapy requires knowledge of how tumor-free tissue responds to the same treatment. The aim of this study was to evaluate standardized uptake values (SUVs) in tumor-free regions of patients with metastatic colorectal cancer prior to and following therapy, via the use of 18-fluoride fluoro-2-deoxy-D-glucose (18F-FDG) positron emission tomography/computed tomography (PET/CT). On baseline 18F-FDG PET/CT scans (n=51), volumes of interest (VOI) were obtained from tumor-free tissue (aortic arch, liver and spleen) and SUVs normalized to total body mass were registered. The procedure was repeated for a follow-up scan two weeks following a single administration of the third-line treatment with irinotecan plus cetuximab. The mean differences in SUV prior to and following therapy were non-significant (P>0.05) in all the registered tumor-free regions. Correlation coefficients indicated a significant result between the variables (0.74-0.84; P<0.001). This study suggests that the early assessment of metabolic response may be made following the administration of third-line therapy with irinotecan plus cetuximab in patients with metastatic colorectal cancer refractory to second-line treatment with irinotecan.