One of the most exciting developments in cancer research in recent years has been the clinical validation of molecularly targeted drugs that inhibit the action of pathogenic tyrosine kinases. Treatment of appropriately selected patients with these drugs can alter the natural history of their disease and improve survival. The clinical validation of these "first-generation" tyrosine kinase inhibitors has been the prelude to a second wave of advances in molecular targeting that is expected to further change the way we classify and treat cancer. Efforts are now being directed at identifying the tumor subtypes and patients who will benefit the most from these drugs. In addition, new compounds that circumvent acquired resistance to the first-generation tyrosine kinase inhibitors are being tested in patients with refractory disease. Agents directed against new molecular targets are also being explored.