Risk of incident cancer in patients with Inflammatory Bowel Disease with prior breast cancer: a multicenter cohort study.

Background and 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 IBD patients with a history of breast cancer according to the subsequent IBD treatment provided.

Methods: A multicenter retrospective study included consecutive IBD patients 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 [IQR 6 - 21]), first line treatment (median interval of 28 months [IQR 7 - 64]) was a conventional immunosuppressant in 19.3 % of patients, anti-TNF in 19.8 %, vedolizumab in 7.2 % and ustekinumab in 1.9 %. After a median follow-up of 71 months [IQR, 34 - 148], 42 (20%) incident cancers were observed (34 breast cancer recurrences). Adjusted incidence rates per 1000 person-years were 10.2 (95%CI 6.0- 16.4) for the untreated arm and 28.9 (95%CI 11.6-59.6) for exposed patients (p= 0.0519). There was no significant difference between treated patients and controls regarding incident-cancer free survival rates (p=0.4796). In multivariable analysis, factors associated with incident cancer were stage T4d (p=0.036), triple negative tumor (p=0.016) and follow-up of less than 71 months (p=0.005).

Conclusion: 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.