CAR T-cell therapy is a breakthrough treatment in which a patient's immune system T cells are genetically modified to mount a more effective attack on cancer. To date, the therapy has been approved by the U.S. Food and Drug Administration (FDA) for children and young adults with specific types of leukemia and lymphoma. Recently, trials of the therapy have opened for patients with some types of solid tumors. We discuss who is eligible for the treatment, and who may be eligible for clinical trials.