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

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.

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.

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).

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.