Figure 1

Cancer stem cells (CSCs, yellow) may divide symmetrically (curved black arrows) to generate two identical CSCs; or asymmetrically (red arrows) to self-renew and yield a non-stem cancer cell with a discrete maximum proliferative capacity. Non-stem cancer cells may divide only symmetrically (straight horizontal black arrows), with both parent and daughter experiencing a decrement in proliferative capacity. Mortal non-stem cancer cells with exhausted proliferative capacity die upon the ensuing division attempt. Non-stem cancer cells inherit generational life spans from the parent CSCs, resulting in a hierarchy depth (red to black gradient) that determines tumor population heterogeneity. Shown are hierarchical progressions of tumor populations originating from A) a CSC conferring ρ_max = 4 and B) a CSC conferring ρ_max = 1.