Context: Cancer stem cells from several human malignancies, including poorly differentiated thyroid carcinoma and thyroid cancer cell lines, have been cultured in vitro as sphere-forming cells. These thyroid cancer stem cells were proven to be able to reproduce the original tumor in a xenograft orthotopic model.
Objectives: The objective of the study was to characterize papillary thyroid carcinoma (PTC) spheres from well-differentiated thyroid cancer and normal thyroid (NT) spheres obtained from the contralateral thyroid tissue of the same patient.
Design: Thyrospheres from PTCs and NTs were isolated.
Main outcome measures: Gene expression analysis by real-time PCR, immunofluorescence studies, and fluorescence-activated cell sorter analysis in thyrospheres from PTCs and NTs have been evaluated.
Conclusions: Compared with NT spheres, PTC spheres are larger, more irregular, and more clonogenic and have a higher rate of symmetric division. Moreover, PTC spheres express higher levels of stem cell markers and lower levels of thyroid-specific genes compared with NT spheres. Under appropriate conditions, NT spheres differentiated into thyrocytes, whereas PTC spheres did not, displaying a defect in the differentiation potential. Immunofluorescence experiments indicated that, in NT spheres, progenitor cells are mainly present in the sphere core, and the sphere periphery contains thyroid precursor cells already committed to differentiation. PTC spheres are not polarized like NT spheres. Unlike cells differentiated from NT spheres, TSH did not significantly stimulate cAMP production in cells differentiated from PTC spheres. A microarray analysis performed in paired samples (NT and PTC spheres from the same patient) indicated that NT and PTC spheres display a gene expression pattern typical of stem/progenitor cells; however, compared with NT spheres, PTC spheres display a unique gene expression pattern that might be involved in PTC progression.