EP223 - Progression of Rectal Polyposis following Ileorectal Anastomosis in FAP

Purpose/Background: The natural history of rectal polyps in familial adenomatous polyposis (FAP) patients following total abdominal colectomy with ileorectal anastomosis (TAC/IRA) remains controversial. While early spontaneous regression of rectal polyps post-IRA has been reported in some studies, rectal polyposis is known to progress over time. This study primarily aims to characterize initial rectal polyposis changes post-TAC/IRA by evaluating rectal polyp counts at first surveillance endoscopy post-IRA.

Methods/Interventions: FAP patients post-TAC/IRA (1993-2023) were identified via a hereditary GI neoplasia registry. Change in rectal polyp count was defined as the difference between rectal polyps at baseline (at TAC/IRA) and first follow-up (6-24 months post-IRA). Depending on distribution, differences were reported as means (95% normal-theory CI) or medians (95% distribution-free CI). Paired t-tests and Wilcoxon signed-rank tests were used; negative values indicate a decrease, and positive values an increase in rectal polyp count. A sub-analysis stratified patients by baseline rectal polyp count (0-10, 11-20, >20). A secondary model used continuous baseline rectal polyp count to predict mean 1-year post-IRA rectal polyp counts. Patients without accurate baseline data were excluded.

Results/Outcomes: Among 277 patients (median 6 follow-up endoscopies, range 1-21), the median time from TAC/IRA to first follow-up was 1.5 years (range 0.85-4.4), and median to last follow-up was 8.6 years (range 4.5-16.1). At the time of surgery, 61% (170/277) had 0-10 rectal polyps, 26% (71/277) had 11-20, and 13% (36/277) had more than 20. The final analytic cohort (n = 95) included patients with first follow-up surveillance scope 6-24 months post-TAC/IRA, with a median time to first follow-up of 12.1 months (IQR: 9.2-14.0). Overall, there was no significant reduction in rectal polyp counts from baseline to first follow-up. However, among patients with 0-10 rectal polyps at baseline (n = 49), there was a small but statistically significant increase in rectal polyp count at first follow-up (median difference: 1.0, 95% CI: 0.0 to 2.0; p = 0.02). In contrast, patients with higher baseline rectal polyp counts demonstrated decreases in median polyp counts, though these changes were not statistically significant. Specifically, patients with 11-20 baseline rectal polyps (n = 26) had a median change of -10.0 (95% CI: -14.0 to 3.0; p = 0.11), and those with more than 20 rectal polyps at baseline (n = 20) had a median change of -17.0 (95% CI: -29.0 to 0.0; p = 0.15). Using the entire cohort (n=277), a second model adjusting for continuous baseline rectal polyp count was used to predict mean 1-year post-IRA rectal polyp counts and demonstrated a significant positive association between baseline and follow-up counts (Figure 1).

Conclusion/Discussion: Among FAP patients undergoing TAC/IRA, no significant reduction in rectal polyp count was observed at first follow-up surveillance. These findings indicate that early rectal polyp changes post-IRA vary according to baseline rectal polyp disease severity. This highlights the need for risk-stratified surveillance strategies to optimize timing of post-operative endoscopy and inform surgical management.

Table 1
Change in Rectal Polyp Counts from Baseline at TAC/IRA to First Postoperative Follow-Up
Figure 1
Adjusted Predicted Mean 1-Year Rectal Polyp Counts with 95% Confidence Intervals