FDG PET/CT and Colonoscopy Combine Synergistically in Primary Colorectal Cancer Diagnosis

Colonoscopy is the standard for primary colorectal cancer (CRC) detection, but is invasive and imperfect. This study aimed to assess the accuracy of 18F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) and colonoscopy in the diagnosis of primary CRC. Methods: A retrospective analysis of all patients identified as undergoing an FDG PET/CT scan and a colonoscopy within six months of each other, with no intervening malignancy treatment, over 12 months in a single university teaching hospital. Results: Two hundred and sixty-two patients had FDG PET/CT and colonoscopy within six months. 206 were excluded for prior treatment. 56 patients were included; 26 (46%) with confirmed primary CRC tumors and 30 (54%) without. Multivariate logistic regression analysis indicated that CRC diagnosis was more likely when colonoscopy was performed before the FDG PET/CT (OR: 21.9, CI 2.6-183) and when CRC was diagnosed on FDG PET/CT (OR 12.3, CI 3.0-51.0). The ROC-AUC for FDG PET/CT and colonoscopy was 0.81 (CI 0.70-0.93, P<0.001) and 0.96 (CI 0.90-1.0, P<0.001), respectively. Conclusions: Colonoscopy is very good and FDG PET/CT is good as diagnostic tests for CRC primary diagnosis. Together, they facilitated diagnosis in all primary cases of CRC. PET/CT should be considered in patients with incomplete colonoscopy where there is suspicion for primary CRC