Background: Inflammatory bowel disease (IBD) is commonly treated with immunomodulators such as azathioprine and 6-mercaptopurine (6-MP). Studies examining lymphoma risk in IBD patients treated with these medications have been underpowered and have yielded conflicting conclusions. Aims: The purpose of this meta-analysis was to provide a more precise estimate of the relative risk of lymphoma among IBD patients treated with azathioprine or 6-MP. Methods: Studies were included if they were English language, full article, cohort studies specifically designed to evaluate cancer as an adverse outcome of treatment with azathioprine or 6-MP. Pooled standardised incidence ratios were calculated to estimate the relative risk of lymphoma associated with therapy. Heterogeneity was assessed using Poisson regression. Sensitivity analyses examined the influence of individual studies on risk estimate and heterogeneity statistics. Results: Six studies were identified that met our inclusion criteria. When the data were combined across all studies, the pooled relative risk was 4.18 (95% confidence interval 2.07-7.51; 11 observed cases, 2.63 expected). Sensitivity analysis showed that exclusion of any one study had a relatively small effect on the pooled relative risk estimate (range 3.49-5.21) but excluding either the study with the highest or lowest estimated relative risk eliminated the statistically significant heterogeneity. Conclusions: Our data suggest an approximate fourfold increased risk of lymphoma in IBD patients treated with azathioprine/6-MP. The increased risk of lymphoma could be a result of the medications, the severity of the underlying disease, or a combination of the two.

We assess toxicity related to 6-mercaptopurine in the treatment of inflammatory bowel disease by reporting our experience with 396 patients (120 patients with ulcerative colitis, 276 with Crohn disease) observed over 18 years. Follow-up data for a mean period of 60.3 months were obtained for 90% of the patients. Toxicity directly induced by 6-mercaptopurine included pancreatitis in 13 patients (3.3%), bone marrow depression in 8 (2%), allergic reactions in 8 (2%), and drug hepatitis in 1 (0.3%). These complications were reversible in all cases with no mortality. Most cases of marrow depression occurred earlier in our experience, when the initial drug doses used were higher. Infectious complications were seen in 29 patients (7.4%), of which 7 (1.8%) were severe, including one instance of herpes zoster encephalitis. All infections were reversible with no deaths. Twelve neoplasms (3.1%) were observed, but only 1 (0.3%), a diffuse histiocytic lymphoma of the brain, had a probable association with the use of 6-mercaptopurine. Our data, showing a low incidence of toxicity in 396 patients, coupled with the previously demonstrated efficacy of 6-mercaptopurine in the treatment of inflammatory bowel disease, indicate that the drug is a reasonable alternative in the management of patients with intractable inflammatory bowel disease.

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To test the effectiveness of 6-mercaptopurine (6-MP) in the treatment of Crohn's disease, we entered 83 chronically ill patients into a two-year double-blind study comparing 6-MP with placebo. Crossover data showed that improvement occurred in 26 of 39 courses of 6-MP (67%) as compared with three of 39 courses of placebo (8%) (P less than 0.001). Non-crossover data likewise confirmed the superiority of 6-MP. The drug was more effective than placebo in closing fistulas (31 vs 6%) and in permitting discontinuation or reduction of steroid dosage (75 vs. 36%) (P less than 0.001). The onset of response to 6-MP was often delayed, with 32% of patients taking longer than three months to respond, and 19% taking longer than four months. Adverse side effects to 6-MP occurred in 10% of patients and were uniformly reversible. We conclude that 6-MP is an effective and useful agent in the management of Crohn's disease.

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Carcinoma does arise in the midst of the anorectal fistulas and abscesses of Crohn's disease. Carcinoma arising in a Crohn's disease fistula can be very difficult to diagnose. Examination may be limited by pain, stricture, or induration of the perianal and perineal tissues. Examination under anesthesia can also overlook the lesion. Diagnostic examination under anesthesia yields increases with biopsies or curettage of the fistulous tracts.

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Fistulae are distressing chronic complications of Crohn's disease which have served as one of the most common indications for surgical resection. While steroids and sulfasalazine have not been successful in closing fistulae, in a previous double-blind study 6-mercaptopurine (6-MP) was more effective than placebo in accomplishing this goal (31% vs 6%). Thirty-four patients with Crohn's disease fistulae were treated with 6-MP for a minimum period of 6 months. In 13 patients (39%) the fistulae closed completely, and in another 9 (26%) there was obvious improvement. All types of fistulae responded to 6-MP with the most impressive closures occurring in patients with fistulae of the abdominal wall and enteroenteric fistulae. The mean time to respond was 3.1 months, with 23% of patients taking longer than 4 months to show any response. Response was not related to other drugs (steroids, sulfasalazine) used in conjunction with the 6-MP. The site of intestinal involvement with Crohn's disease did not appear to play a significant role in the frequency or degree of response to 6-MP, but patients without prior resection and fistulae did better than those with fistulae occurring after surgery. The long-term response to fistulae was good if 6-MP was maintained, whereas exacerbation eventually followed discontinuation of 6-MP. 6-Mercaptopurine is an effective and useful drug in the treatment of fistulae, as it is in other manifestations of chronic unrelenting Crohn's disease.