PHILADELPHIA—Treatment with thiopurines is associated with an increased risk of squamous cell carcinoma of the skin in patients with inflammatory bowel diseases.

An article in Clinical Gastroenterology and Hepatology discussed results of a study that looked at outcomes of patients with IBD who developed SCC while receiving thiopurine therapy.1

Researchers from Corporal Michel J. Crescenz VAMs and the Perelman School of Medicine at the University of Pennsylvania conducted a retrospective cohort study of 54,919 patients with IBD followed in the nationwide VA health system from Jan. 1, 2000, through May 23, 2018.

A subcohort was created of patients with an incident diagnosis of SCC, confirmed by review of patients’ medical records. The study team looked at those who had received treatment with thiopurines (exposed group) vs. those treated with mesalamine and no prior exposure to thiopurines or tumor necrosis factor antagonists (unexposed group). Identifying 467 patients with incident SCC, researchers included 449 patients (161 exposed and 288 unexposed) in their final analysis.

Defined as the primary outcome was death associated with SCC. Among the data collected were baseline demographic features, exposure to ultraviolet light, Charlson comorbidity index, smoking status and environmental exposures. For the study, follow-up began at the time of incident SCC diagnosis and ended at death or last recorded date in the health system. 

With 11 patients dying from complications of SCC, including 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. The study calculated the unadjusted and adjusted cause-specific HRs for SCC mortality associated with exposure as 7.0 (95% CI, 1.8-28.0; P = .006) and 8.0 (95% CI, 2.0-32.8; P = .004), respectively.

“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 mesalamine,” the study authors concluded.

1. 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.