Diarrhea and colitis related to immune checkpoint inhibitor and BRAF/MEK inhibitor therapy.

Background: Immune checkpoint inhibitor (ICI) therapy can be complicated by gastrointestinal adverse events (AEs). Similarly, gastrointestinal AEs have been reported with the use of serine/threonine-protein kinase B-Raf (BRAF) and mitogen-activated protein kinase kinase (MEK) inhibitor therapy. We investigated the characteristics and management of gastrointestinal AEs related to sequential ICI and BRAF/MEK inhibitor therapy. Methods: We identified 255 adult cancer patients who received both BRAF/MEK inhibitor therapy and ICI therapy between 2014 and 2021. Thirty-two eligible patients had gastrointestinal AEs after receiving both therapies and were categorized based on the order of their administration. Their clinical characteristics, evaluation, treatment and outcomes were compared. Results: Of the 32 eligible patients, 18 (56.3%) received ICI therapy followed by BRAF/MEK inhibitors (early ICI group), and 14 (44.8%) received BRAF/MEK inhibitor therapy followed by ICI (early BRAF/MEK inhibitor group). Compared with the early BRAF/MEK inhibitor group, the early ICI group had higher rates of grade 3-4 diarrhea (50.0% vs. 14.3%, P=0.047) and grade 3-4 colitis (38.9% vs. 0%, P=0.010). The early ICI group had a later onset of colitis (347.5 vs. 84.5 days, P=0.011) and a higher rate of hospitalization at initial colitis presentation (100% vs. 71.4%, P=0.028). Patients in the early ICI group were more likely to have diarrhea or colitis recurrence (69.2% vs. 9.1%, P=0.019) and re-hospitalization for colitis (38.9% vs. 0%, P=0.010). Conclusion: The sequential exposure of BRAF/MEK therapy after ICI may contribute to a more aggressive clinical profile of gastrointestinal toxicities that may warrant a more aggressive management strategy.