ABCG2 and cancer: Studies on oral premalignant lesions have shown that CSC markers, such as ABCG-2 and Bmi-1, predict the transformation of oral leukoplakia to cancer.51 The expression patterns of CSC markers, such as ALDH1 and CD133, correlate with a high risk of malignant transformation of oral leukoplakia.52 In addition, the coexpression of the CSC markers ALDH1 and Bmi-1 is a strong indicator of malignant transformation of oral erythroplakia.20 It is well established that the CSC markers ALDH1, Bmi-1 and ABCG-2 drive the process of field cancerization in oral erythroplakia.53,54