Background
Both NMSC and IBD primarily manifest in the Caucasian population. Given the predominance of Caucasians in the New Zealand population, and New Zealand’s specific latitude and ozone layer depletion, it is not surprising that NZ has amongst the highest rates of both IBD and NMSC. This is a major concern as thiopurine immunosuppression in IBD patients in NZ predisposes these patients to even higher risk of NMSC, given the peak background levels of the disease.
Aims
The aim of this study was to investigate the rate of non-melanoma skin cancer in patients with inflammatory bowel disease treated with thiopurine immunomodulators (azathioprine and mercaptopurine) in New Zealand.
Methods
180 thiopurine-immunosuppressed IBD patients from Dunedin and North Shore (Auckland) were examined to investigate the incidence of NMSC. Age- and gender-matched controls were recruited in both centres. All patients and controls completed a consent form and study questionnaire. Participants then received a full body skin examination to identify the presence of a suspicious skin lesion. Suspicious lesions were filmed and reviewed by the study dermatologist who then made recommendations as to which lesions require further following by the patient’s general practitioner.
Results
359 participants were recruited (Auckland controls n=87, Auckland patients n=83, Dunedin controls n=92, Dunedin patients n=97) with a mean age of 41.4. Overall 43.2% were male. Among the 180 patients, AZA doses were available for 157 with 145 known to have used AZA for at least 6 months (median duration 42 mo, range 6 mo–300 mo). Out of the 145 patients who had received AZA, 13 cases of skin cancers were recalled, compared to 6 among the 201 who did not receive AZA. An additional 16 suspicious lesions were found among the AZA group (including 2 for patients already with a history of skin cancer) and 8 among the non-AZA group. Based on the mean 60.4 months of AZA use reported, this would give crude incidence rates for skin cancer or suspicious lesions of 37/1000 patient years for the AZA group and 14/1000 patient years for the non-exposed group. From unadjusted regression, AZA use of 6 mo or more was associated with higher risk of skin cancer or suspicious lesions (RR 2.67, 95% CI 1.40–5.10, p=0.003). This association persisted after separately adjusting for confounders (skin complexion, age, gender, tanning bed use, sunblock use and duration of sun exposure).
Conclusion
The results of this project support reports of increased risk of NMSC in IBD patients with use of thiopurines, as suggested by international studies. Despite peak background rates of NMSC in New Zealand, thiopurines raised NMSC risk even further. It was also evident immunosuppressed IBD patients were generally unaware of their increased NMSC risk and experience poor sun-safety. The majority of patients denied prior skin checks. As a result of our findings, it is recommended that IBD patients be advised regarding NMSC and sun safety, and also be scheduled for regular skin monitoring. These services can be provide by the IBD nurse.
