Primary cancer metastasis to thyroid gland is rare. The most common metastatic tumors of the thyroid gland are from lung, breast and renal cell carcinoma. In this case report, a patient with breast cancer metastasized to the thyroid gland is presented. A 38-year-old female patient was diagnosed with breast cancer, and positron emission tomography-computed tomography (PET-CT) imaging for breast cancer staging revealed fluoro-2deoxy-D-glucose (FDG) uptake in the thyroid nodule. Fine needle aspiration biopsy (FNAB) of the nodule revealed atypia of undetermined significance (Bethesda III). After neoadjuvant chemotherapy, simultaneous breast conserving surgery and total thyroidectomy were performed. Immunohistochemical staining of the pathological specimens revealed breast cancer that had metastasized to the thyroid gland. Immunohistochemical methods helped distinguishing primary thyroid cancer from metastasis. Also, nodules that showed activity involvement were detected randomly in PET-CT, and had to be evaluated in terms of malignancy.