What is this summary about?This article describes the results of a clinical research study called ‘CheckMate 901’,which was published in The New England Journal of Medicine. CheckMate 901 was a study that looked at a specific type of cancer called urothelial cancer, which impacts parts of the urinary system. Participants in the study had urothelial cancer that was either unresectable (meaning that it cannot be removed by surgery) or metastatic(where the cancer has spread from the urinary system to other parts of the body).Unresectable or metastatic urothelial cancer is normally treated with chemotherapy(treatment using chemicals to kill fast-growing cancer cells), but researchers are looking for more effective treatment options. The CheckMate 901 study aimed to find out if using a combination of chemotherapy and the drug nivolumab would work better and last longer than chemotherapy alone for people with advanced urothelial cancer. Immunotherapies are a family of cancer treatments that use the body's own immune system to fight the cancer.What happened in the study?In the CheckMate 901 study, researchers looked at nivolumab plus chemotherapy given together compared with chemotherapy alone as first-line treatment (the first treatment used) for people with metastatic urothelial cancer. The goal of the study was to see if this combination(nivolumab plus chemotherapy) would work better than chemotherapy alone in terms of how long people survived (lived) and how long they survived without their cancergetting worse. The study also looked at any side effects (undesirable effect of the drug) and other health problems that might come from these treatments.What do these results mean?In comparing people who received nivolumab plus chemotherapy together, followed by nivolumab by itself, with people who received chemotherapy alone, the results showed that people in the nivolumab plus chemotherapy group not only survived (lived) longer, but also survived (lived) longer without their cancer getting worse. They were also more likely to have their tumors (an abnormal growth of body tissue) shrink, and were more likely to have their tumors shrink completely (and maintain complete shrinkage for a longer period of time). Also, they experienced no difference in overall health-related quality of life, and had similar side effects to those seen in other studies of nivolumab or chemotherapy.[Box: see text].