What happened, in summary

A 53-year-old woman was evaluated in early 2023 after finding a mass in her left breast. Imaging showed a tumor a little over 2 centimeters, with no evidence of distant spread. A biopsy raised concern for invasive cancer, and she underwent a total mastectomy with sentinel lymph node testing. Surgery confirmed Stage II invasive ductal breast cancer. None of the 8 sampled sentinel lymph nodes contained cancer. The tumor was HER2-positive and negative for estrogen and progesterone receptors.

She then started chemotherapy together with HER2-targeted therapy. About 1 week after her first cycle, she developed severe abdominal pain and diarrhea. Her symptoms improved with supportive care, but they returned after the second cycle, and colonoscopy showed significant inflammation and an ulcer in the colon.

Because the bowel problem persisted, her medical team changed the chemotherapy while continuing HER2-targeted treatment. She completed 6 further cycles without another major gastrointestinal complication. A follow-up colonoscopy in August 2023 showed that the ulcer had healed.

She continued HER2-targeted therapy through March 2024. By April 2025, follow-up evaluation showed no evidence that the breast cancer had returned.