A Case Report on the Development of Ulcerative Colitis During Osimertinib Therapy for Epidermal Growth Factor Receptor Mutation-Positive Non-Small-Cell Lung Cancer.

Osimertinib, a standard treatment for epidermal growth factor receptor (EGFR)-positive non-small-cell lung cancer, commonly causes manageable diarrhoea. We report osimertinib-induced refractory diarrhoea diagnosed as ulcerative colitis, remitting with mesalazine. A 69-year-old woman with advanced-stage EGFR mutation-positive lung adenocarcinoma developed persistent diarrhoea 3 weeks after starting osimertinib, complicated by anorexia, hypotension, anaemia and renal failure requiring hospitalisation. While anaemia and renal failure improved after osimertinib cessation, diarrhoea persisted. A colonoscopy revealed ulcerative colitis, confirmed by neutrophil and lymphocyte infiltration in the intestinal mucosa, glandular deformation and decreased goblet cells. This case demonstrates that osimertinib-induced ulcerative colitis was successfully treated with mesalazine.