These therapies have generally been developed to treat cancers where the driver gene has a “gain of function” mutation that causes cancer onset and progression. The goal of the therapies is to inhibit the newly acquired function of the gene itself or the pathways induced by the gene. Driver genes with a gain of function mutation, also known as oncogenes, are responsible for approximately 30% of all cancers. Most other cancers are driven by “loss of function” mutations in driver genes that normally suppress the onset of cancer. These driver genes are called tumor suppressor genes, and when mutated, they and their products cannot be targeted directly as their function is already turned off.