Case Report: A rare case of thyroid metastasis from breast cancer.

INTRODUCTION: To analyze the clinicopathological features, diagnosis, and treatment strategies for metastatic breast carcinoma to the thyroid (MBCT) to enhance clinical awareness of this rare condition. METHODS: Analysis of clinical data from one MBCT patient and literature review. RESULTS: A 41-year-old female with left breast invasive ductal carcinoma (IDC) received neoadjuvant AC-T chemotherapy, breast-conserving surgery, radiotherapy, and endocrine therapy. At eight years post-diagnosis, thyroid lesions were detected. Total thyroidectomy with lymph node dissection confirmed MBCT pathologically. No progression was observed at 16 months post-thyroidectomy. CONCLUSIONS: MBCT is a rare clinical entity characterized by nonspecific clinical and radiological findings. Immunohistochemical (IHC) analysis is essential for a definitive diagnosis. In patients with a breast cancer history, MBCT should always be considered in the differential diagnosis of thyroid abnormalities.