What is this summary about?This is a plain language summary of an article originally published in the Journal of Clinical Oncology. It is about the long-term results from a clinical study called JAVELIN Bladder 100. This study looked at whether avelumab maintenance treatment and the best supportive care would help people with advanced urothelial cancer live longer than the best supportive care only. Avelumab is a type of medicine called immunotherapy, which helps the body’s immune system fight cancer.People with advanced urothelial cancer often receive chemotherapy as their first treatment (also called first-line treatment). Although the cancer may get better at first, it is likely to start growing again after chemotherapy has ended. Maintenance treatment aims to stop the cancer from growing again. People also receive supportive care, which includes treatments such as antibiotics, pain-relief medicine, and nutritional supplements or support. Supportive care helps to manage symptoms but does not shrink the cancer or stop it from growing.The JAVELIN Bladder 100 study included 700 people with advanced urothelial cancer who were treated in 29 countries. The first results from the study showed that avelumab maintenance treatment helped people with advanced urothelial cancer live longer than people who did not receive this treatment. These results led to avelumab maintenance treatment becoming the standard treatment around the world for people with advanced urothelial cancer that has stopped growing or shrank with first-line chemotherapy.This summary reports long-term results from the study. Researchers wanted to find out if avelumab maintenance treatment was still helping people live longer, at least 2 years since starting treatment.What were the results?Long–term results showed that 50% of people who received avelumab maintenance treatment were still alive 2 years after starting the study compared with 38% of people who did not receive avelumab. On average, people who received avelumab maintenance treatment lived 9 months longer than people who did not receive avelumab. Researchers also found that the long-term safety results (side effects) for avelumab maintenance treatment were similar to earlier results. No new side effects were seen with longer avelumab maintenance treatment.What do these results mean?Long-term results from the JAVELIN Bladder 100 study show ongoing benefits and long–term safety with avelumab maintenance treatment. These updated results provide further support for using avelumab maintenance as the standard treatment for people with advanced urothelial cancer that stopped growing or shrank with first–line chemotherapy.[Box: see text].