There is controversy over whether the treatment of patients with ulcerative colitis with thiopurines increases their risk of lymphoma.
Dr Nabeel Khan and colleagues from Louisiana, USA evaluated the risk of lymphoma among thiopurine-treated patients with ulcerative colitis.
The researchers obtained nationwide data from the Veterans Affairs (VA) health care system from 2001 to 2011.
The team performed a retrospective cohort study, analyzing data on 36,891 patients from their date of diagnosis of ulcerative colitis in the VA health care system to a diagnosis of lymphoma or 2011.
Thiopurine exposure was assessed using the VA pharmacy database.
|Incidence rates of lymphoma were 2.3 per 1000 person-years in those treated with thiopurines|
Patients who developed lymphoma were identified based on ICD-9 codes and confirmed by manual chart review.
In total, 4734 patients with ulcerative colitis were treated with thiopurines for a median of 1 year.
The research team observed that lymphoma developed in 119 patients who had not been treated with thiopurines, 18 who were treated with thiopurines, and 5 who had discontinued treatment with thiopurines.
The incidence rates of lymphoma were 0.60 per 1000 person-years among patients who had not been treated with thiopurines, 2.3 among patients who were treated with thiopurines, and 0.28 among patients who had discontinued treatment with thiopurines.
The incidence rates of lymphoma during the first year, second year, third year, fourth year, and more than 4 years of thiopurine therapy were 0.9, 1.6, 1.6, 5, and 8.9 per 1000 person-years, respectively.
The age-, sex-, and race-adjusted hazard ratios of developing lymphoma were 4.2 while being treated with thiopurines, and 0.5 after discontinuing treatment with thiopurines compared with patients who had not been treated with thiopurines.
Dr Khan's team concludes, "Based on a retrospective, nationwide cohort study, patients with ulcerative colitis have a 4-fold increase in risk of lymphoma while being treated with thiopurines compared with patients who have not been treated with thiopurines."
"The risk increases gradually for successive years of therapy. Discontinuing thiopurine therapy reduces the risk of lymphoma."