Figure 2.

Mixed model for the nature of sustained tumor growth. The tumor is originally driven by rare cells of one phenotype (CSC1, yellow), which may have stem/progenitor cell origin and give rise to the tumor bulk by producing terminally differentiated cells (blue). Subsequent mutations enhancing self-renewing capacity create a dominant subclone that is phenotypically different (CSC2, green) and more aggressive. If the CSC2 subclone does not display “stem-like” cell properties, such a subset will not be able to initiate tumors with a high frequency [30].