Ectopic thyroid cancer is rare, but not beyond the realm of possibility

In infrequent cases, clumps of thyroid cells can develop from birth in bodily sites other than the gland itself. Called ectopic thyroid, this tissue is subject to cancer just like any other organ, leading in rare instances to ectopic thyroid cancer (ETC).

A new literature review appearing in the Journal of Clinical Endocrinology and Metabolism attempted to estimate the prevalence of such cases, ultimately finding just 400 reported cases of ETC.

The authors, a team of U.S. and Polish endocrinologists from six hospitals and research institutes, said that ectopic thyroid tissue alone, without any cancerous growth, is only found in about one in 10,000 people.



Multiplying by the figure of one in 111 - the lifetime risk of thyroid cancer published by the National Cancer Institute - one could estimate that fewer than one in 1.1 million Americans are ever diagnosed with ETC. However, even this number may be overstating it.



Even so, researchers warned that doctors should be aware of ETC when examining undiagnosed lumps in the throat or neck. After all, the meta-study found that a significant portion of ETC patients had lingual thyroid, in which functional thyroid tissue is found in a lump within the muscles forming the base of the tongue.

Distant ectopic thyroid tissue is exceedingly rare. For instance, a 1963 literature review published in the Annals of Surgery put the number of cases of struma cordis (functional thyroid tissue found in the heart) and struma ovarii (thyroid tissue located in the ovaries) in the single digits.

Nevertheless, any such tissue is technically vulnerable to cancer. The authors of the new meta-study recommended thyroidectomy, neck dissection and radioactive iodine therapy for lingual or cervical ETC.

Scientists added that, of the 400 or so recorded cases of lingual ETC, the majority were of the medullary variety, even though papillary thyroid cancer is more common among all patients with thyroid carcinomas. 
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