An Advanced Triple Positive Breast Cancer Developed Endometrial Metastasis After Anti-HER2-Based Therapy Failed: A Case Report and Review

Early endometrial metastasis from triple-positive breast cancer is a rare phenomenon in young patients, especially when anti-human epidermal growth factor receptor 2 (HER2) target therapy is used as the primary treatment. We present a case of a 24-year-old patient with advanced triple positive breast cancer. The patient developed abnormal uterine bleeding during chemotherapy combined with anti-HER2 therapy (trastuzumab plus pyrotinib). Due to the transvaginal sonography are not characteristic and the low incidence rate of endometrial metastasis from breast cancer, this potential diagnosis was overlooked. The disease progressed rapidly thereafter, and the overall survival was only 13 months. The swift and devastating progression highlight the immense challenges in managing such complex cases. It remains a current challenge to identify such cases at an early stage and explore more effective therapeutic regimens. Based on this case review and previous studies, we speculate that disease progression might be attributed to the absence of endocrine therapy, chemotherapy resistance, or insufficient anti-HER2 therapeutic intensity. This case provides new insights into the metastatic pattern of HER2-positive breast cancer under targeted drug resistance. Clinicians should be alert to the possibility of reproductive system metastasis during anti-tumor treatment. Timely diagnosis and appropriate treatment are expected to improve patient prognosis.