PHILADELPHIA—Treatment with thiopurines is associated with an increased risk of squamous cell carcinoma of the skin in patients with inflammatory bowel diseases, according to a new study.

Researchers from the Corporal Michel J. Crescenz VAMC and the University of Pennsylvania Perelman School of Medicine, both in Philadelphia, studied outcomes of patients with IBD who developed SCC while receiving thiopurine therapy.

Results of the retrospective cohort study of 54,919 patients with IBD followed in the nationwide VA Healthcare System from Jan. 1, 2000, through May 23, 2018, were reported in Clinical Gastroenterology and Hepatology.1

From the larger cohort, the study team created a subcohort of patients with an incident diagnosis of SCC, confirmed by review of patients’ medical records. Those who had received treatment with thiopurines (exposed group) vs. those treated with 5-ASA and no prior exposure to thiopurines or tumor necrosis factor antagonists (unexposed group) were identified.

Defined as the primary outcome was death associated with SCC (SCC mortality). Data also was collected on baseline demographic features, exposure to ultraviolet light, Charlson comorbidity index, smoking status and environmental exposures.

For the study, followup began at the time of incident SCC diagnosis and ended at death or last recorded date in the health system. Cause-specific hazard models were used to estimate the adjusted and unadjusted hazard ratio, with 95% CIs, for SCC mortality.

Overall, 467 patients with incident SCC and included 449 patients—161 exposed and 288 unexposed—were used in the final analysis. Of those, 11 patients died from complications of SCC, eight in the exposed group and three in the unexposed group.  The estimated five- and 10-year cumulative mortality values were 2.9% and 2.9% in the exposed group and 0.4% and 0.9% in the unexposed group, respectively, according to the researchers.

The unadjusted and adjusted cause-specific HRs for SCC mortality associated with exposure were 7.0 (95% CI, 1.8-28.0; P=.006) and 8.0 (95% CI, 2.0-32.8; P=.004), respectively, the study calculated.

“Although the cause-specific mortality is relatively low, patients with IBD exposed to thiopurines who develop SCC have an increased risk of SCC-associated death compared to patients exposed to only 5-ASA,” study authors concluded.

Khan N, Lee H, Trivedi C, Kavani H, Medvedeva E, Xie D, Lewis JD, Yang YX. Mortality Associated With Development of Squamous Cell Cancer in Patients With Inflammatory Bowel Disease Receiving Treatment With Thiopurines. Clin Gastroenterol Hepatol. 2019 Mar 7. pii: S1542-3565(19)30254-X. doi: 10.1016/j.cgh.2019.03.005. [Epub ahead of print] PubMed PMID: 30853615.