Ear Nose Throat J. 2006 Aug;85(8):480, 483.
FIRST PARAGRAPH: Tumors that occur in the thyroid gland as a result of lymph or vascular spread from distant sites are considered to represent metastatic disease rather than a direct extension of a primary from an adjacent organ. Metastatic deposits are identified at a higher frequency in abnormal glands—that is, those with adenomatoid nodules, thyroiditis, and follicular neoplasms. Further, metastatic deposits may be found within primary thyroid tumors, such as a renal cell carcinoma metastatic to a thyroid papillary carcinoma. Although a thyroid gland mass may be the presenting clinical sign, it is more often the underlying thyroid gland disease (e.g., thyroiditis, adenomatoid nodules) that prompts clinical evaluation. The thyroid gland metastatic deposit is the initial presentation of an occult primary tumor in as many as 40% of patients. Carcinomas are the most common metastatic tumors from (in order of frequency) the kidney (figure 1), lung, breast (figure 2), and stomach; melanoma is less common.
PubMed ID: 16999049
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