A subtractive thyroid cDNA library was constructed from two human thyroid carcinoma cell lines originating from an anaplastic carcinoma and a papillary thyroid carcinoma. The library was used to identify genes correlated with the progression to a highly malignant phenotype. The thymosin β-10 gene was isolated and found to be expressed at much higher levels in the anaplastic cell line than in the papillary cells. The thymosin β-10 gene was overexpressed in five carcinoma cell lines compared with normal thyroid tissue and normal thyroid primary culture cells. The highest expression occurred in the most malignant cell lines. Thymosin β-10 gene expression was also increased in surgically removed human thyroid carcinomas and was highest in the anaplastic carcinomas.

Thymosin β-10 gene expression was correlated with the degree of the malignant phenotype also in rat thyroid cells transfected with cellular and viral oncogenes of different tumorigenicity. These results show that thymosin β-10 overexpression is a general event of thyroid cell neoplastic transformation and suggest that the gene is involved in the progression of thyroid carcinogenesis. Finally, the thymosin β-10 gene was located on chromosome 2q37 by fluorescence in situ hybridization analysis.