[A case of hyoid bone metastasis from breast cancer]

A 69-year-old woman had undergone breast conserving surgery and axillary lymph node dissection for left breast cancer 10 years previously. The tumor was positive for estrogen receptor (ER) and progesterone receptor (PgR), and negative for human epidermal growth factor receptor-2 (HER2). Adjuvant tamoxifen and radiation therapy were administered to the conserved breast for 5 years. The patient detected a painless neck mass 1 year previously. Computed tomography (CT) revealed a hyoid bone mass, and fine needle aspiration cytology indicated a diagnosis of adenocarcinoma. Positron emission tomography combined with CT (PET-CT) revealed masses in the pelvis, spine, hyoid bone, and cervical lymph node. For definitive diagnosis, excisional biopsy of the hyoid bone was performed. Immunohistostaining revealed that the cells were CK7 (+), CK20(-), mammaglobin (+), GCDFP-15 (+), ER (+), PgR (+), and HER2 (-). The final diagnosis was multiple bone metastasis(hyoid, pelvis, spine)as well as cervical lymph node metastasis from breast cancer. After diagnosis, the patient was treated with anastrozole and denosumab, and she achieved a partial response. She has experienced progression free survival for 12 months. Metastasis to the hyoid bone is uncommon for breast cancer. We report a case in which hormone therapy was effective after it was selected based on the results of excisional biopsy.