Postoperative positron emission tomography–computed tomography (PET-CT) in patients (Pts) with pathological stage III colon cancer (CC): Results from the first prospective validation study.

Abstract

3621 Background: A significant proportion of pts with pathological stage III CC recur despite the absence of metastatic disease on pre-operative imaging. In a previous large retrospective study from our group on 348 pts, we reported that early postoperative PET-CT modified the staging and management of 13.4% of pathological stage III CC pts. The aim of the current study was to prospectively validate these findings. Methods: A prospective, single-center study of pts with pathological stage III CC who underwent early postoperative PET-CT (< 3 months from surgery) between the years 2013-2023. All pts had no evidence of overt or equivocal metastatic disease at pre-operative CT-based imaging. Results: 144 pts were accrued and 134, 50% males, median age 67 years (range, 21-92) were evaluable for the primary endpoint i.e. early postoperative PET-CT results. Pathological stage was IIIA, IIIB and IIIC in 9 (6.7%), 81 (60.4%) and 44 (32.8%) pts, respectively. The median number of lymph nodes examined and of positive nodes were 19 (range, 6-134) and 2 (range, 0-26), respectively. The median time from surgery to PET-CT was 1.7 months (range, 0.9-3.2). Post-operative PET-CT findings were significant in 18 pts (13.4%): 12 pts (9.0%) were upstaged to stage IV, 4 (3.0%) were diagnosed with a second primary malignancy, 1 (0.7%) was both upstaged and diagnosed with another cancer and one pt (0.7%) had local recurrence. Metastatic sites identified by the PET-CT were liver (9 pts), peritoneum (4), lymph nodes (2) and lung (1), and the second malignancies detected by the test were breast in 2 pts and thyroid, palatine tonsil and rectum in one pt each. Of the 13 pts found to have metastatic disease, 5 (38.4%) underwent potentially curative surgery. At a median follow-up of 39.0 months (range, 4.7–123.3), 20 of the 116 pts (17.2%) with true stage III CC recurred; the estimated 3-year disease-free survival rate was 83.9%. The estimated 5-year overall survival rate for the entire cohort was 85.2%; the rates for true stage III pts and for pts found to have metastatic disease were 89.8% and 56.2%, respectively ( P<0.0001). Conclusions: Results from the first prospective study to evaluate the role of early postoperative PET-CT in pts with pathological stage III CC have validated earlier retrospective data: the use of PET-CT in this setting changed the staging and management of 13.4% of pts, allowing early detection of potentially curable metastatic disease or other malignancies. Moreover, the stage migration phenomenon observed in our study, seems to have an impact on the pts overall outcome, compared to the literature. In light of the accumulating data from our center, suggesting a favorable cost-benefit of early postoperative PET-CT in pathological stage III CC, incorporation of the test into the routine management of these pts should be considered.