Case report review highlights suspicion of breast cancer metastasis to thyroid in a 54-year-old woman

Metastatic thyroid cancer originating from breast cancer is rare and often misdiagnosed in clinical practice. Early identification, diagnosis, and treatment are the main way to improve prognosis. This case reports describes a unique case of breast cancer metastasis to the thyroid 16 years after the diagnosis of breast cancer in order to enhance clinicians awareness to this rare disease.Case reportA 54-year-old woman was diagnosed with left breast ductal carcinoma + invasive lobular carcinoma (T2N2M0, stage IIIA) 16 years ago. Her condition became stable after radiotherapy, chemotherapy, and endocrine therapy. Recent physical examination indicated a C-TIRADS-4B mass in the right thyroid gland, which was indicative of thyroid malignancy. Radical thyroid surgery was performed for thyroid cancer. Postoperative pathology and immunohistochemistry revealed that the cancer originated from the breast and positron emission tomography–computed tomography (PET-CT) indicated multiple systemic bone metastases. After multidisciplinary consultation, endocrine therapy and chemotherapy were administered. Currently, the patient is alive.ConclusionBreast cancer metastasis to the thyroid is rare. If a patient with a history of breast cancer has newly developed thyroid nodules, the clinician should highly suspect the origin of the tumor. Preoperative FNAB and immunohistochemistry are the main methods for diagnosis and surgery is the major treatment.