ABCG2 and renal cell carcinoma: The stemness‐associated genes were analysed using RT‐qPCR, and the results showed that the mRNA levels of Nanog, Sox2, Oct4, CD44, CD133, ABCB1, ABCC1, ABCG2 and Notch1 were significantly increased in RCC tumour spheres compared with parental cells (Figure 1C).