Jedd D. Wolchok, MD, PhD (Damon Runyon-Lilly Clinical Investigator ‘03-‘08) and colleagues at Memorial Sloan Kettering Cancer Center, New York, reported a key discovery that explains why some patients respond to Yervoy/ipilimumab, an immunotherapy drug, while others do not. They found that the cancer cells from patients who respond to the drug carry a high number of genetic mutations—some of which make tumors more visible to the immune system, and therefore easier to fight. In the future, the researchers hope to develop a diagnostic test to detect the mutations in melanoma patients, which could help doctors to make more effective treatment decisions. This study was published in The New England Journal of Medicine.