Squamous cell carcinoma of the thyroid gland: primary or secondary disease?

Department of Otolaryngology and Head and Neck Surgery, Southern General Hospital, Greater Glasgow and Clyde NHS Trust, Glasgow, UK.
The Journal of Laryngology & Otology (Impact Factor: 0.7). 10/2010; 125(1):3-9. DOI: 10.1017/S0022215110002070
Source: PubMed

ABSTRACT To review the aetiopathogenesis, clinical characteristics, immunohistochemical profile, prognosis and treatment options for primary thyroid squamous cell carcinoma, and to compare it with squamous cell carcinoma metastatic to the thyroid, thus providing the reader with a framework for differentiating primary and secondary disease.
Review of English language literature from the past 25 years.
A search of the Medline, Embase and Cochrane databases (April 1984 to April 2009) was undertaken to enable a comprehensive review.
After applying strict criteria for the diagnosis of primary thyroid squamous cell carcinoma, 28 articles were identified reporting 84 cases. When reviewing secondary thyroid squamous cell carcinoma, we only analysed cases of squamous cell carcinoma metastatic to the thyroid gland, and found 28 articles reporting 78 cases.
It is possible to differentiate between primary and secondary thyroid squamous cell carcinoma, on the basis of combined evidence from clinical examination and endoscopic, pathological and radiological evaluation. Such differentiation is important, as the prognosis for primary squamous cell carcinoma is uniformly poor irrespective of treatment, and the most suitable option may be supportive therapy. Treatment for secondary squamous cell carcinoma of the thyroid varies with the site and extent of spread of the primary tumour.

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    ABSTRACT: KIT, a tyrosine kinase receptor protein encoded by the proto-oncogene c-kit, is overexpressed in human neoplasms such as gastrointestinal stromal tumors and thymic squamous cell carcinoma. However, the role of KIT expression and mutations in carcinoma showing thymus-like elements is not fully understood. In the current study, 8 cases of carcinoma showing thymus-like elements were reported, and immunohistochemical staining with KIT and CD5 was performed. Mutation analyses in the juxtamembrane domains (exons 9 and 11) and in the tyrosine kinase domains (exons 13 and 17) were performed on KIT-positive samples using polymerase chain reaction and direct DNA sequencing. KIT- and CD5-positive stainings were observed in all 8 cases. However, none of the tested samples showed mutations in any of the 4 exons. The primary carcinoma showing thymus-like elements of the thyroid frequently expresses KIT and CD5 proteins; similar to thymic squamous cell carcinoma, the overexpression of KIT does not necessarily indicate a gene mutation in this tumor. KIT, along with CD5, could be a useful marker for the difficult diagnosis of carcinoma showing thymus-like elements, which should be added to the list of KIT-positive neoplasms.
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