Clinicopathological Features of Second Primary Colorectal Cancer Incidentally Identified by 18F-FDG-PET

As positron emission tomography using F18-fluorodeoxyglucose (FDG-PET) is becoming a common imaging modality the number of colorectal cancers incidentally detected by FDG-PET is expected to increase. In this study, we investigated the clinicopathological features of 15 cases of second primary colorectal cancer incidentally detected by PET during other cancer evaluation in patients who underwent surgery. We also discussed the significance of FDG-PET in evaluating cancer status. None of the patients had undergone FDG-PET for suspected colorectal disease; 6 were being evaluated by FDG-PET for lung cancer, 5 for nasopharyngeal or laryngeal cancer, 3 for gastrointestinal cancer, and 1 for uterine cancer. The average tumor size was 36.1 ± 14.4 mm (range, 25-70 mm) and the mean maximum standardized uptake value (SUVmax) was 11.9 ± 6.0 (range, 3.0-29.6). Although 4 cases (26.7%) had distant metastasis, 3 (20%) were Tis or T1 cancer, 3 (20%) were T2 cancer. Of the 15 cases, 6 (40%) could have been underwent laparoscopic surgery. Our study found that asymptomatic cases of colorectal cancer can be detected by FDG-PET during evaluation for other cancer. Therefore, in some cases, FDG-PET is useful for detecting second primary colorectal cancer at a relatively early and curable stage.