Drug-induced colitis on BRAF and MEK inhibitors for BRAF V600E-mutated non-small cell lung cancer: a case report.

Introduction The combination of BRAF and MEK inhibitors has deeply changed the treatment of BRAF V600-mutant non-small cell lung cancer patients. These agents demonstrated high antitumor activity as well as safe and manageable toxicity profile. Hypertension, pyrexia and increased liver enzymes are the most common adverse events. Gastrointestinal toxicities are rare, and mainly consist of mild grade vomiting and diarrhea. Case report We report the case of 70-year-old man affected by BRAF V600-mutant NSCLC with bilateral lung and bone metastases. First-line treatment with encorafenib (450 mg once daily) and binimetinib (45 mg twice daily) was administered within a clinical trial. At the first radiological assessment, computed tomography (CT) scan showed a partial response and signs of intestinal inflammation were reported. The investigational treatment was timely withheld. The subsequent colonoscopy demonstrated the presence of ulcerative lesions at the caecal tract, and the histological diagnosis suggested a drug-induced colitis. No specific treatment was given as the patient did not report abdominal disturbances. Forty-five days after treatment interruption a new CT scan showed the resolution of bowel inflammation and investigational treatment was resumed at the same doses. The patient is still alive and free of toxicity recurrence after 11 months from treatment initiation. Conclusion. Severe gastrointestinal toxicities are uncommon with BRAF and MEK inhibitors, although cases of colitis and intestinal perforation have already been reported in literature. The pathogenesis seems to be related to the MAPK pathway inhibition performed by MEK inhibitors. These adverse events should be accounted given the potential to evolve into life-threatening conditions.