Inhibition of notch1/2 by MRK-003 or Numb resulted in down-regulation of the stemness markers CTR2, BCL-2, OCT-4, KLF4 and MDR1 (Fig. 4e–h), reduced self-renewal (Fig. 4i and j), invasive and migration capability (Fig. 4k–n), enhanced sensitivity to cisplatin and sorafenib (Fig. 4o–r), and decreased tumorigenicity (Fig. 5a and Table 2) in RCC CSCs. This evidence concerns the gene KLF4 and renal cell carcinoma.