The OnPrime study is testing a new treatment for women with certain types of ovarian cancer that have not responded to regular platinum-based treatments. **Olvi-Vec** is a special virus used to help the immune system attack cancer cells. It is given directly into the belly using a tube, called an *intraperitoneal catheter*. After that, patients receive regular cancer drugs, such as *platinum-doublet chemotherapy* and *bevacizumab*. The study will compare this new method to regular treatments chosen by doctors. **Key Points:** - The study involves a single cycle of Olvi-Vec given over two days, followed by other medications. - Participants will be closely monitored for safety and effectiveness. - The study requires patients to have specific types of ovarian cancer and meet health criteria. Patients need to have had several previous treatments and should not have certain health problems like active infections or severe heart disease. The study aims to see if Olvi-Vec helps patients live longer and feel better. Participants will be observed for any side effects and how well the treatment works. For more details, interested individuals should discuss with their healthcare provider.