A123 NON-MELANOMA SKIN CANCER IN IBD PATIENTS TAKING 6-TGN ANTIMETABOLITES A POPULATION STUDY

Abstract

Background

Non-melanoma skin cancer (NMSC) rates have been shown to increase in Inflammatory Bowel Disease (IBD) patients taking 6-thioguanine (6-TGN) antimetabolites (Azathioprine and 6-Mercatopurine). There is limited population-based data assessing the risk of NMSC in IBD patients on 6-TGN and anti-tumor necrosis factor (anti-TNF) therapy.

Aims

To determine the risk of NMSC amongst IBD patients on 6-TGN antimetabolites and anti-TNF therapies in a longitudinal, population-based Canadian cohort

Methods

This was a retrospective cohort study using population-based administrative data from Saskatchewan (1970 to 2011). IBD and NMSC cases were identified through application of validated administrative definitions to ICD billing codes. Using population-based drug dispensal data IBD cases were classified as “exposed” and “unexposed” to each of 6-TGN antimetabolites and anti-TNF therapies. Univariate and multivariate conditional logistic regression and cox-proportional hazard analyses were performed. Hazard ratios were adjusted for age, sex, location, and medication.

Results

A total of 8713 prevalent IBD cases were identified for inclusion, 51.6% CD and 48.4% UC. There were 349 cases of NMSC, 68 patients were exposed to 6-TGN and 281 non-exposed. The unadjusted hazard ratio (HR) was 0.74 in IBD patients exposed to 6-TGN compared to non exposed, p 0.0276 (95% CI 0.57–0.97). Stratified by age (<50 or 50 and older) the adjusted HR was 1.18 in IBD patients <50 years old, p 0.40 (0.8–1.74) and 1.38 ≥50 years old, p 0.1708 (0.87–2.20). The adjusted HR in CD patients < 50 years old was 1.08, p 0.7531 (0.67–1.73) and 1.78 ≥50 years old, p 0.030 (1.06–3.00). The adjusted HR in UC patients < 50 years old was 1.32, p 0.4232 (0.67–2.57) and 0.47 ≥50 years old, p 0.2624 (0.12 – 1.77)

Conclusions

Overall, lower rates of NMSC in IBD patients taking 6-TGN compared to those not exposed to 6-TGN were observed. However when stratified for age CD patients greater than age 50 exposed to 6-TGN had statistically higher rates of NMSC compared to those not exposed, suggesting an age-related effect. Analyses to better understand the association between 6-TGN on NMSC risk which explore cumulative exposure to 6-TGN therapy and the impact of anti-TNF on NMSC will be performed. This study contributes additional data that further elucidates the relationship between 6-TGN exposure and development of NMSC

IBD Type	Number of events with exposure	Unadjusted			Adjusted
		HR	95% CI	p-value	HR	95% CI	p-value
Age < 50 years only
IBD (159/6228)	43	0.96	0.67–1.36	0.7989	1.18	0.8–1.74	0.4015
CD (85/3400)	32	0.91	0.58–1.41	0.6623	1.08	0.67–1.73	0.7531
UC (74/2828)	11	1.04	0.55–1.97	0.906	1.32	0.67–2.57	0.4232
Age 50+ years only
IBD (190/2455)	25	1.32	0.86–2.01	0.203	1.38	0.87–2.20	0.1708
CD (91/1096)	22	1.52	0.94–2.46	0.0863	1.78	1.06–3.00	0.0300
UC (99/1389)	<6	0.49	0.16–1.56	0.2285	0.47	0.12–1.77	0.2624

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