According to a study published in Gastroenterology, ongoing and past exposure to thiopurines significantly increases the risk of nonmelanoma skin cancer (NMSC) in patients with inflammatory bowel disease (IBD).

The prospective observational study involved a cohort of 19,486 patients with IBD in whom the incidence of NMSC was determined in comparison to data from the general population, used for reference, from the French Network of Cancer Registries.

The following results were reported:

• Before the age of 50 years, the crude incidence rates of NMSC among patients currently receiving or who previously received thiopurines were 0.66/1000 and 0.38/1000 patient-years, respectively; these values were 2.59/1000 and 1.96/1000 patient-years for the age group of 50 to 65 years and 4.04/1000 and 5.70/1000 patient-years for patients older than 65 years.

• Among patients who had never received thiopurines, the incidence of NMSC was zero before the age of 50 years, 0.60/1000 for the ages of 50 to 65 years, and 0.84/1000 for those older than 65 years.

The researchers concluded that patients with IBD who have past or present thiopurine exposure are at increased risk for developing NMSC, even before the age of 50 years, and these patients should be protected against UV radiation and receive lifelong dermatological screening.

A separate study in the same issue of the journal evaluated the risk of NMSC among patients with IBD with and without exposure to immunosuppressant medications.

The Canadian study involved a total of 9618 individuals with IBD (55% women; 51% with Crohn’s disease) who were followed up for a median of 11.7 years (interquartile range, 5.7–18.7 years) and 91,378 individuals without IBD (55% women) who were followed- up for a median of 11.5 years (interquartile range, 5.7–18.8 years). The following results were reported:

• Of the 237 individuals with IBD diagnosed with NMSC, 203 (86%) were diagnosed with basal cell skin cancer (BCC). Among the individuals without IBD, 1800 were diagnosed with NMSC, of which 1493 (82%) were diagnosed with BCC (hazard ratio, 1.20; 95% confidence interval [CI], 1.03–1.40) compared with controls.

• Among individuals with IBD exposed to immunosuppressant medications, there was a 4- to 7-fold increased relative risk (hazard ratio, 3.83–7.11) of squamous cell skin cancer (SCC), as compared with individuals without IBD (hazard ratio, 5.40; 95% CI, 2.00–14.56), compared with controls.

The researchers concluded that this study suggests that use of thiopurines increases the risk of SCC among individuals with IBD and patients with IBD and their physicians should be reminded about skin care (use of sun protection strategies and not to ignore new skin lesions), especially among those exposed to thiopurines.