Endocrine Abstracts

Using gene expression profiling we found that the CBX7 gene was drastically down-regulated in six thyroid carcinoma cell lines versus control cells. This suggested that CBX7 is an oncosuppressor. The aim of this study was to determine whether CBX7 is related to thyroid cancer phenotype, and to try to identify new tools for the diagnosis and prognosis of thyroid cancer. We thus evaluated CBX7 expression in various snap-frozen and paraffin-embedded thyroid carcinoma tissues of different degrees of malignancy by quantitative RT-PCR and immunohistochemistry, respectively. CBX7 expression progressively decreased with malignancy grade and neoplasia stage. Indeed, it decreased in an increasing percentage of cases going from benign adenomas to papillary (PTC), follicular and anaplastic (ATC) thyroid carcinomas. This finding coincides with results obtained in rat and mouse models of thyroid carcinogenesis. CBX7 loss of heterozygosity occurred in 36.8% of PTC and in 68.7% of ATC. Restoration of CBX7 expression in thyroid cancer cells reduced growth rate, which indicates that CBX7 plays a critical role in the regulation of transformed thyroid cell proliferation. In conclusion, loss of CBX7 expression correlates with a highly malignant phenotype in thyroid cancer patients. Consequently, CBX7 monitoring could contribute to thyroid cancer diagnosis and prognosis.