N08C9 (Alliance): A Phase 3 Randomized Study of Sulfasalazine Versus Placebo in the Prevention of Acute Diarrhea in Patients Receiving Pelvic Radiation Therapy.

Purpose: To provide confirmatory evidence on the use of sulfasalazine to reduce enteritis during pelvic radiation therapy (RT), following 2 prior single-institution trials suggestive that benefit existed.

Methods And Materials: A multi-institution, randomized, double-blind, placebo-controlled phase 3 trial was designed to assess the efficacy of sulfasalazine versus placebo in the treatment of RT-related enteritis during RT including the posterior pelvis (45.0-53.5 Gy) and conducted through a multicenter national cooperative research alliance. Patients received 1000 mg of sulfasalazine or placebo orally twice daily during and for 4 weeks after RT. The primary endpoint was maximum severity of diarrhea (Common Terminology Criteria for Adverse Events version 4.0). Toxicity and bowel function were assessed by providers through a self-administered bowel function questionnaire taken weekly during RT and for 6 weeks afterward.

Results: Eighty-seven patients were enrolled in the trial between April 29, 2011, and May 13, 2013, with evenly distributed baseline factors. At the time of a planned interim toxicity analysis, more patients with grade ≥3 diarrhea received sulfasalazine than received placebo (29% vs 11%, P=.04). A futility analysis showed that trial continuation would be unlikely to yield a positive result, and a research board recommended halting study treatment. Final analysis of the primary endpoint showed no significant difference in maximum diarrhea severity between the sulfasalazine and placebo arms (P=.41).

Conclusions: Sulfasalazine does not reduce enteritis during pelvic RT and may be associated with a higher risk of adverse events than placebo. This trial illustrates the importance of confirmatory phase 3 trials in the evaluation of symptom-control agents.