A gut fix for a cancer treatment side effect? Immune checkpoint inhibitors (ICIs) are powerful cancer-fighting drugs — but they can trigger serious gut inflammation that forces patients to pause treatment. A new phase 1/2 trial out of MD Anderson Cancer Center tested fecal microbiota transplantation (FMT) as a first-line response to this complication, and the early results are encouraging.

In 13 patients with cancer who developed ICI-related diarrhea and colitis, a single FMT delivered via colonoscopy led to clinical response in 77% of cases, with symptoms improving in a median of just 1.5 days. Among those who responded, 80% maintained remission through a median 6.5-month follow-up. Crucially, 11 of 13 patients were able to resume some form of cancer treatment after their gut symptoms resolved.

By the Numbers:

• 76.9% of patients achieved clinical response within 2 weeks of FMT
• Median symptom improvement: 1.5 days after treatment
• 80% of initial responders maintained sustained remission
• 75% of sequenced stool samples showed increased microbial diversity post-FMT
• Fecal calprotectin (inflammation marker) dropped from 416 mcg/g → 146 mcg/g
• Side effects were mild (grade 1 only): fever, gas, nausea, and abdominal pain in 23% of patients

Why it matters: ICI-related colitis is a major reason cancer patients have to stop immunotherapy — a potentially life-altering interruption. If FMT can resolve symptoms quickly while reducing reliance on immunosuppressive steroids, it could become a meaningful addition to oncology supportive care. Larger, controlled trials are needed to confirm these findings.