The four genes (ALDH1A1, CD44, OCT3/4, and ABCG2) chosen to detect their expression levels in all 39 samples of PTC as well as in 11 thyroid fibroadenoma samples were selected for their potential role as cancer stem cell markers in thyroid cancer and their potential importance in thyroid cancer initiation and progression [24–26]. This evidence concerns the gene ABCG2 and cancer.