Malignancy Risk with Thiopurines

Based on a large retrospective, nationwide cohort study, it has been estimated that patients with ulcerative colitis have a 4-fold increase in the risk of lymphoma compared with patients who have not been treated with thiopurines (Gastroenterol 2013; 145: 1007-15).  While this study enrolled data from 36,891 patients followed for a median of 6.7 years, this study should not be interpreted in isolation.  The editorial (pages 927-30) provides some important context.

Besides the risk of lymphoma in patients treated with the thiopurines, the editorial briefly states the potential for life-threatening infections, primarily varicella and hemophagocytic lymphohistiocytosis which may complicate primary EBV infection.  The latter is much more common in younger patients.

With regard to malignancy, besides lymphoma, thiopurines also increase the frequency of nonmelanoma skin cancer.  Since these are not life-threatening, in many patients the risk of lymphoma is “the major limiting factor for the prolonged use of thiopurines.”  Furthermore, the risk of lymphoma may increase relative to treatment duration according to the above-referenced study. The editorial notes that there are three types of lymphoma to be considered:

  1. Posttransplant-like lymphoma associated with EBV seropositivity. Absolute risk in all IBD patients ~ 1 per 1000 patient-years.  All EBV-seropositive patients are at risk.
  2. Early post-mononucleosis lymphomas. Absolute risk in all IBD patients ~0.1 per 1000 patient-years; however, the risk in young men who are seronegative for EBV (<35 years) is ~3 per 1000 patient-years.
  3. Hepatosplenic T-cell lymphomas.  Absolute risk in all IBD in all IBD patients ~0.05 per 1000 patient-years; again, in young patients (mostly men) the risk is ~0.1 per 1000 patient-years.

The second and third types of lymphomas can be reduced by limiting thiopurines in young men.

Despite the risks posed by thiopurines, the overall benefit-risk balance needs to consider the fact that the risk of colorectal cancer “is markedly reduced in patients with long-standing extensive colitis exposed to thiopurines.”  Thus, the lowered risk of colorectal cancer “may outweigh the excess risk of lymphoma.”

Also, in considering thiopurines:

Inflamm Bowel Dis 2013; 19: 2801-08.  “Thiopurines are Associated with a Reduction in Surgical Re-resections in Patient’s with Crohn’s Disease.”  This study was a retrospective review of 567 patients of whom 237 (41.8%) developed a surgical recurrence after a median of 70 months.  Taking thiopurine was associated with a hazard ratio of 0.51.  Due to small numbers, the results with anti-TNF therapy was not conclusive, but “seems promising as well.”

Related blog posts:

1 thought on “Malignancy Risk with Thiopurines

  1. Pingback: Cancers Complicating Inflammatory Bowel Disease | gutsandgrowth

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