Thyroid Metastasis from Primary Breast Cancer.

Breast cancer (BC), the most commonly diagnosed malignancy, frequently metastasizes to the bone, lungs, brain and liver at advanced stages, whereas the thyroid gland represents a rare target site for secondary disease. We examined the most recent literature about thyroid metastasis (TM) from BC after we encountered a peculiar case of a 71-year-old woman who developed sudden dysphagia, severe hypothyroidism and hypoparathyroidism due to TM 18 years after the diagnosis of her primary cancer. Based on published data, the prevalence of TM in BC ranges from 3% to 34%, with a median onset time of 48.2 months, although longer time intervals are not infrequent. TM negatively impacts the prognosis of these patients, however thyroid surgery can limit the local disease burden. Therefore, we suggest that clinicians involved in the follow-up care of BC patients should consider a differential diagnosis of secondary thyroid malignancy when incidental lesions are diagnosed during radiological evaluations or local symptoms affect the cervical region, even many years after the diagnosis of the primary cancer.