Fig. 1.

TICs display pronounced plasticity: self-renewal as well as tumor-initiation capacities of TICs are not restricted to phenotypically immature cells. Spheroid cultures display increased chemoresistance and expression of stemness markers, as well as reduced proliferation, compared to adherent differentiated counterparts. However, both spheroids and adherent counterparts have comparable self-renewal capacities and can lead to similar tumor formation when low cell numbers (10 cells per injection) are injected subcutaneously into immune-deficient mice