Patients with advanced melanoma whose cancer does not respond to treatment with widely used immunotherapy drugs known as PD-1 inhibitors are often switched to treatment with a second type of immunotherapy drug—a CTLA-4 inhibitor such as the drug ipilimumab. New results from a clinical trial by the SWOG Cancer Research Network show that these patients are more likely to benefit from ipilimumab when it is given in combination with the PD-1 inhibitor nivolumab than when given alone.