After nearly 100 years of development, treatments that empower the body's immune system to fight cancer are maturing and saving patients' lives. When 71-year-old Maureen Sideris was treated for colon cancer in 2008, she had to undergo surgery. Her treatment was successful, but the recovery process after the operation was exhausting. Fourteen years later, Sideris was diagnosed with esophageal cancer, and this time, her treatment, offered through a clinical trial, looked completely different. Every three weeks, she traveled to the Memorial Sloan Kettering Center in New York for 45-minute infusions of a drug called dostarlimab. After just four months of treatment, Sideris's tumor had disappeared—without surgery, chemotherapy, or radiation. And yet, it is real. Sideris is one of a growing number of patients benefiting from immunotherapy, a method that is reaching its peak. It brings the promise of personalized therapy, long-term remission, and fewer side effects than traditional methods. "People are living, and living with a good quality of life. We are talking about cures," says Jennifer Wargo, a professor of surgical oncology in Texas. The body has a natural ability to detect and eliminate cells that do not belong to it. But sometimes, cancerous cells "trick" the system, hiding in plain sight. The goal of immunotherapy is to unmask these cells. Two of the best-known forms are: CAR T-cell therapy, where protective cells (T-cells) are extracted from the patient's blood, modified in the laboratory to attack cancer, and reinjected. It is currently used mainly for blood cancers, and checkpoint inhibitors, where these drugs deactivate an "off switch" of the immune system, which cancer uses to avoid being targeted. The scientists who discovered this won the Nobel Prize in 2018.