Epithelial-mesenchymal transitions during cell culture of primary thyroid tumors?

Fibroblast contamination of epithelial tumor cell cultures is of great concern when examining tumor cells in vitro for specific biochemical and cytogenetic changes. The observations of normal karyotypes in thyroid tumor cell cultures have raised the concern of whether residual tissue fibroblasts might obscure the cytogenetic analysis of transformed epithelial cells. We have characterized early passaged thyroid tumor cells to examine the proportions of epithelial and fibroblastic cell types. Cells were analyzed by immunocytology using antibodies recognizing the thyroid prohormone thyroglobulin, epithelial cytokeratins, and vimentin, a mesenchyme marker. Tumors consisted of one follicular adenoma and five papillary carcinomas. When examined by day 15 in culture, all cells contained filaments composed of vimentin, which most likely represents an adaptation to culture conditions. Double immunofluorescence staining for thyroglobulin and cytokeratin revealed the presence of not only epithelial but also spindle-like fibroblastoid cells possessing thyroid epithelial cell markers. The results suggest that in thyroid tumor cultures there is a unique cell type intermediate between epithelial and mesenchyme phenotypes that must be considered when performing cytogenetic analysis.