To the Editor: We read with interest the article by Kopylov et al, particularly with respect to the increased risk of nonmelanoma skin cancer (NMSC) seen in patients with inflammatory bowel disease (IBD) on thiopurines. Previous studies have also shown that patients with IBD with previous and ongoing exposure to thiopurines are at increased risk. Importantly, unlike lymphoma risk,4 the risk of NMSC persists even after discontinuation of thiopurines, suggesting a mechanism of nonreversible DNA damage
