In stratified analyses, the incidence of nonmelanoma skin cancer during thiopurine use increased with patient age from younger than 40 years to 40-65 years to older than 65 years (0.6, 9.1, and 12.2 per 1,000 person-years); was greater among patients living in high-UV zones versus low- or medium-UV zones (10.3 vs. 6.0 per 1,000 person-years); and increased with number of VA visits annually from fewer than six, to 6-12, and then more than 12 (1.2, 9.4, and 12.3 per 1,000 person-years).
Finally, the rate rose with the cumulative duration of exposure to thiopurines. It increased steadily during the first 2 years of use, stabilized through the fourth year of use, and rose sharply in the fifth year of use to 13.6 per 1,000 person-years.
Dr. Abbas disclosed no relevant conflicts of interest.
*Correction 12/10/13: A previous version of this article incorrectly reported Dr. Ali Abbas' university affiliation. This version has been updated.