Using flow cell sorting technique, we analysed TPO expression on papillary (NPA), follicular (ML1 and WRO) and anaplastic (SW1736 and C643) human thyroid cancer cell lines, and showed that TPO is present on all the cell lines tested even though it was found less expressed in anaplastic and follicular thyroid cancer when compared to papillary carcinoma. This evidence concerns the gene TPO and thyroid cancer.