Figure 2.

Heterogeneity of tumors and types of drug responses and resistance starting from no response at 1st line (primary resistance) via partial response to complete response with or without residual disease. In 2nd line treatment with a different drug the same type of reactions can be expected. In that case, no response means cross-resistance of the two different drugs is happening. Color codes: Red circles: cancer stem cells; other colors: different tumor cell types; cross-hatched circles: aggressive/metastasizing cell types