BACKGROUND: Chemotherapy is a cornerstone of systemic treatment for breast cancer. Common adverse effects include nausea, vomiting, diarrhea, and myelosuppression; chemotherapy-induced colitis is rare, and its underlying mechanisms remain unclear. We aim to raise awareness of this uncommon but serious adverse event and describe a practical approach to regimen modification.

CASE REPORT: A 53-year-old woman underwent left total mastectomy for invasive breast carcinoma (pT2N0M0, Stage IIA; ER [-]/PR [-]/HER2 [3+]). She received adjuvant chemotherapy with the TCbHP regimen (docetaxel, carboplatin, trastuzumab, and pertuzumab). One week after the first cycle, she developed abdominal pain and diarrhea. Colonoscopy revealed colitis. After dose reduction to 80% in the second cycle, abdominal pain recurred, and colonoscopy demonstrated colonic ulcers. The regimen was subsequently changed to THP (nab-paclitaxel, trastuzumab, and pertuzumab); symptoms then resolved, and follow-up colonoscopy showed ulcer healing.

CONCLUSIONS: Colitis associated with breast cancer chemotherapy is rare, presenting diagnostic and therapeutic challenges. Severe complications, including colonic necrosis, may develop if not promptly addressed. In the present case, timely intervention and regimen modification prior to the onset of intestinal necrosis appeared to prevent serious sequelae, including the need for intestinal resection. However, given the limitations of a single case report and the use of combination chemotherapy, a definitive causal relationship cannot be established.

Keywords: Breast Neoplasms, Chemotherapy, Adjuvant, Colitis