A metastatic thyroid tumor (MTT) arising from breast carcinoma (BC) is rare and sometimes difficult to diagnose. We present a case of MTT from BC; we suspected anaplastic thyroid carcinoma at initial presentation. The patient was a 58-year-old female with a hard nodule in the right anterior neck and a history of breast cancer. Computed tomography indicated tumors on both thyroid lobes, and ultrasonography (US) with shear wave measurement (SWM) showed malignant features. We performed fine needle aspiration cytology (FNAC), the results of which led us to strongly suspect MTT from BC. The surgically resected specimen was evaluated histopathologically, including by immunohistochemistry (IHC), and the diagnosis was confirmed. In addition to FNAC and IHC, SWM is useful to diagnose MTT from BC.
Keywords: breast carcinoma (BC); fine needle aspiration cytology (FNAC); immunohistochemistry (IHC); metastatic thyroid tumor (MTT); shear wave measurement (SWM).