Figure 1.

Types of resistance mechanisms occurring in patients. Resistance to targeted therapies can be broadly classified as either de novo or acquired resistance. In case of de novo resistance (top), pre-existing mutations exist in tumor cells that are selected for after treatment (blue colored cells). This could potentially be overcome by treating with sequential selective kinase inhibitors that target escape mechanisms of resistance (orange-colored cells). In acquired resistance (bottom), cells with resistance arise during treatment and cause relapse. Sequential treatments may overcome resistance if given in correct order.