Smoking and colorectal neoplasia in patients with inflammatory bowel disease: Dose‐effect relationship

BACKGROUND AND AIMS: Prior studies on the effect of smoking on the risk of colitis‐associated colorectal neoplasia (CRN) have reported conflicting results. We aimed to further elucidate the association between smoking, including possible dose‐effects, and the development of colorectal neoplasia in patients with inflammatory bowel disease (IBD). METHODS: We performed a prospective multicenter cohort study including patients with colonic IBD enrolled in a surveillance program in four academic hospitals between 2011 and 2021. The effects of smoking status and pack‐years at study entry on subsequent recurrent events of CRN (including indefinite, low‐ and high‐grade dysplasia, and colorectal cancer [CRC]) were evaluated using uni‐ and multivariable Prentice, Williams, and Peterson total‐time Cox proportional hazard models. Adjustment was performed for extensive disease, prior/index dysplasia, sex, age, first‐degree relative with CRC, primary sclerosing cholangitis, and endoscopic inflammation. RESULTS: In 501 of the enrolled 576 patients, at least one follow‐up surveillance was performed after the study index (median follow‐up 5 years). CRN occurred at least once in 105 patients. Ever smoking was not associated with recurrent CRN risk (adjusted hazard ratio [aHR] 1.04, 95% confidence interval [CI] 0.75–1.44), but an increasing number of pack‐years was associated with an increased risk of recurrent CRN (aHR per 10 pack‐years 1.17, 95% CI 1.03–1.32; p < 0.05). Separate analyses per IBD type did not reveal differences. CONCLUSIONS: This study found that an increase in pack‐years is associated with a higher risk of recurrent CRN in patients with IBD, independent of established CRN risk factors (NCT01464151).