Treatment and survival of non-metastatic rectal cancer in patients with inflammatory bowel disease: nationwide cohort study.

Background: Patients with inflammatory bowel disease have an increased risk of colorectal cancer. There is a scarcity of large studies with a focus on rectal cancer in patients with inflammatory bowel disease. This study aimed to compare survival in resected patients with rectal cancer with and without inflammatory bowel disease.

Methods: This national population-based study used the Colorectal Cancer Data Base. All Swedish patients ≥18 years of age with a diagnosis of stage I-III rectal cancer between 1997 and 2021, surgically treated with curative intent, were included and followed up until 2022. The outcome of interest was recurrence-free survival. Flexible parametric survival models adjusted for time since surgery, year of diagnosis, sex, age at diagnosis, and Charlson Co-morbidity Index were used to estimate proportional and time-dependent hazard ratios of recurrence-free survival with 95% confidence intervals.

Results: Overall, 22 082 patients with rectal cancer were included, among whom 323 (1.5%) had inflammatory bowel disease. Neoadjuvant radiotherapy/chemoradiotherapy was given to 55% and 63% of patients with and without inflammatory bowel disease respectively. The median follow-up time was 5.2 years (interquartile range (i.q.r.) 2.3-10) in patients with inflammatory bowel disease and 5.9 years (i.q.r. 2.9-10) in patients without inflammatory bowel disease. Based on the adjusted proportional hazards model, no overall difference in recurrence-free survival was found (HR 1.05, 95% c.i. 0.87 to 1.26). In the time-dependent adjusted model, patients with rectal cancer with inflammatory bowel disease experienced a lower recurrence-free survival during the first year after surgery (1 year HR 1.36, 95% c.i. 1.06 to 1.73), after which there was no difference in comparison with patients without inflammatory bowel disease (5 years HR 0.77, 95% c.i. 0.56 to 1.06).

Conclusion: Despite lower recurrence-free survival during the first year among those with inflammatory bowel disease, there were no long-term differences between patients with or without inflammatory bowel disease.