Thiopurines have been taking the rap for non-melanoma skin cancers in patients with IBD – but a new Australian study suggests that researchers may have been looking in the wrong place.

According to research presented at the 12th Congress of the European Crohn’s and Colitis Organisation (ECCO) in Barcelona, UV exposure and skin type were more important than thiopurine exposure in the development of skin cancers.

Dr Clare Wu, a gastroenterologist at Sydney’s St Vincent’s Hospital, told the limbic a study of 691 patients from four specialist IBD centres in Australia and New Zealand did not support an association between thiopurine exposure and non-melanoma skin cancers.

“In our univariate analysis we found an association between thiopurine and skin cancer however with multivariate analysis, the association became not significant.”

There was no association with thiopurine dose, duration or levels of its metabolite 6-thioguanine nucleotides (6-GTN) and skin cancer.

Instead, age, place of residence, sun exposure and skin type were the significant factors.

Participants from Brisbane, a city with the highest UV exposure index of the four study sites, had more than three times the risk of developing non-melanoma skin cancers compared to participants from Christchurch with the lowest UV exposure.

Never staying in the shade contributed almost four times the risk than mostly using shade, and skin that never tans contributed almost seven times the risk as other skin types.

Dr Wu said the information could be used to better target dermatology reviews.

For example, people with dark skin who spend a lot of time indoors may not require as frequent skin cancer checks as a fair-skinned Queenslander who enjoys the outdoors.

“Patients with IBD are already being screened for bone health and via national screening programs. We want to prescribe screening for conditions that are real risks but we don’t want to screen excessively.”