Risk of Incident Cancer in Patients With Inflammatory Bowel Disease With Prior Breast Cancer: A Multicenter Cohort Study.

Background & Aims: Breast cancer is the most common malignancy observed in patients with inflammatory bowel diseases (IBD). The aim of our study was to evaluate incident cancer rate (recurrence or new-onset cancer) in a cohort of patients with IBD with a history of breast cancer according to the subsequent IBD treatment provided.

Methods: A multicenter retrospective study included consecutive patients with IBD with prior breast cancer. The inclusion date corresponded to the diagnosis of index malignancy. Follow-up lasted from cancer diagnosis until the occurrence of incident cancer.

Results: Among 207 patients included (median disease duration, 13 years [interquartile range, 6-21]), first-line treatment (median interval of 28 months [interquartile range, 7-64]) was a conventional immunosuppressant in 19.3% of patients, anti-tumor necrosis factor in 19.8%, vedolizumab in 7.2%, and ustekinumab in 1.9%. After a median follow-up of 71 months (interquartile range, 34-148), 42 (20%) incident cancers were observed (34 breast cancer recurrences). Adjusted incidence rates per 1000 person-years were 10.2 (95% confidence interval, 6.0-16.4) for the untreated arm and 28.9 (95% confidence interval, 11.6-59.6) for exposed patients (P = .0519). There was no significant difference between treated patients and control subjects regarding incident cancer-free survival rates (P = .4796). In multivariable analysis, factors associated with incident cancer were stage T4d (P = .036), triple negative tumor (P = .016), and follow-up of less than 71 months (P = .005).

Conclusions: We did not find a statistically significant increase in incident breast cancer related to IBD treatment beyond the already known poor prognostic factors of breast cancer.