Occult breast cancer metastasis to the thyroid gland: Case report

Thyroid metastases of occult breast cancer are very rare. A 48‐year‐old female patient presented with chronic bone pain, bone, liver and thyroid nodules, and pleural effusion. Histopathological result of the thyroid showed poorly differentiated papillary thyroid carcinoma. However, clinical laboratory and immunohistochemistry studies showed breast origin of the thyroid lesion. Any thyroid mass may be a secondary neoplasm and occult breast cancer should also be considered among the primary sources in spite of its rarity. Immunohistochemistry can play an important role in detecting the origin of malignancy.