Postoperative PET-CT in patients (pts) with pathological stage III colon cancer (CC): Interim results from the first prospective validation study.

Abstract

e15599 Background: A substantial number of pts with pathological stage III CC recur despite the absence of metastatic disease on pre-operative CT. In a previous large retrospective study from our institution on 348 pts, we reported that early postoperative PET-CT modified the staging and management of 13.4% of assumed stage III CC pts. The aim of the current study was to prospectively validate these results. Methods: A prospective, single-center study of pts with pathological stage III CC who underwent early postoperative PET-CT between the years 2013-2021. Results: 83 pts were accrued and 81 (48.1% males, median age 66y) were evaluable for the primary endpoint i.e. PET-CT results. Pathological stage was IIIA, IIIB and IIIC in 7 (8.6%), 56 (69.1%) and 17 (21%) of pts, respectively. Median number of lymph nodes examined and of positive nodes were 17 (range, 9-134) and 2 (range, 0-15), respectively. Post-operative PET-CT findings were significant in 7 pts (8.6%): 4 pts (4.9%) were upstaged to stage IV, 2 (2.5%) were diagnosed with a second primary malignancy, and 1 (1.2%) was both upstaged and diagnosed with another cancer. Three additional pts (3.7%) are currently undergoing evaluation for suspicious PET-CT findings. At a median follow-up of 30.6 months (range, 6.2-92), 13 of the 71 pts with true stage III CC recurred; the estimated 3y disease-free survival rate was 81%. The estimated 5y overall survival rates for the entire cohort and for true stage III pts were 82% and 90%, respectively. Of the 5 pts found to have metastatic disease based on PET-CT findings, one is scheduled to undergo potentially curative surgical removal of a solitary liver metastasis. Conclusions: Interim results from the first prospective study to evaluate the impact of early postoperative PET-CT in pts with pathological stage III CC seem to support earlier retrospective data: the use of PET-CT in this setting changed the staging and management of 8.6% of pts, including the possibility for early detection of potentially curable metastatic disease. Additional data, with more pts and longer follow-up, will be presented at the meeting.