Laurent Beaugerie and colleagues from the St Antoine Hospital in Paris studied data from 19,486 patients who had Crohn's disease or ulcerative colitis.
The patients were assessed over an average of 35 months.
The researchers found that patients' risk of developing lymphoproliferative disorders was over five times higher for those treated with thiopurines, compared with those who had never received the drugs.
Old age, male sex and longer duration of inflammatory bowel disease were also associated with an increased risk of incident lymphoproliferative disorder.
However, the absolute risk remains low, the researchers pointed out, at around 90 cases per 100,000 patients.
The researchers believe that the excess risk may be due to the inflammatory process itself, or to thiopurine exposure, or to a combination of the two.
However, they said that it was not clear whether the risk of incident lymphoproliferative disorder was also increased in patients receiving other immunosuppressants.
In addition, they do not suggest that use of thiopurines should be reconsidered.
'Extrapolating our results, the absolute cumulative risk of lymphoproliferative disorder in young patients receiving a 10-year course of thiopurines remains low (<1%) and does not undermine the positive risk-benefit ratio of these drugs,' they said.
'For elderly patients and unlimited treatment periods, the question should be addressed in dedicated studies,' they added.
