Here's what the fda says:
The U.S. Food and Drug Administration (FDA) is informing the public that it continues to receive reports of a rare cancer of white blood cells (known as Hepatosplenic T-Cell Lymphoma or HSTCL), primarily in adolescents and young adults being treated for Crohn’s disease and ulcerative colitis with medicines known as tumor necrosis factor (TNF) blockers, as well as with azathioprine, and/or mercaptopurine.
www.fda.gov/Drugs/DrugSafety/ucm250913.htmIt's hardly a sure thing, just a small increased risk.