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. Author manuscript; available in PMC: 2009 Jul 6.
Published in final edited form as: J Control Release. 2007 May 13;122(3):385–391. doi: 10.1016/j.jconrel.2007.05.005

Figure 7. Two scenarios concerning the relationship between tumorigenicity/clonogenicity and constitutive MDR expression.

Figure 7

On the left the frequency of MDR+ and tumorigenic cells are both 10%, but they overlap substantially. As in normal tissues, sorting MDR+ cells would yield a substantial enrichment in clonogenic cells. On the right MDR+ cells and tumorigenic cells also constitute 10% of the tumor population, but they only overlap by 10%. Sorting MDR+ cells in this case would result in no enrichment of tumorigenic cells. Importantly, in both cases a fraction of tumorigenic cells are protected by constitutive MDR activity and therefore inherently therapy resistant.