Efficacy and Safety of BG-C9074 With Bevacizumab Compared With Bevacizumab in Adults With Ovarian, Fallopian Tube, or Primary Peritoneal Cancers

Ovarian cancer is a disease where abnormal cells in the ovaries or fallopian tubes grow out of control and form tumors. Common early signs include belly bloating, pelvic or back pain, feeling full quickly when eating, and frequent urination. BG-C9074 is a targeted cancer medicine called an antibody-drug conjugate (ADC). ADC consists of an antibody linked to a drug that can kill cancer cells. The antibody part of BG-C9074 specifically attaches to a protein called B7-H4 that is found on the surface of cancer cells. After it attaches to B7-H4, BG-C9074 enters the cancer cell where the drug causes DNA damage and cell death. Bevacizumab is an approved medicine used to treat these cancers along with chemotherapy. It works by cutting off the blood supply that helps the tumor grow, which may help keep the cancer under better control. The purpose of this study is to test if BG-C9074 is safe and effective in women with advanced epithelial ovarian, fallopian tube or primary peritoneal cancer when it is given in combination with bevacizumab as a first-line maintenance treatment. This study has 2 treatment groups. Participants will be randomly assigned (by chance, like flipping a coin) to receive one of the treatments listed below: * Arm A: BG-C9074 + Bevacizumab * Arm B: Bevacizumab This study will enroll approximately 600 participants. The overall time to participate in this study may be up to 5 years. Participants will make regular visits to the clinic for treatment, health checks, blood tests, and for tumor and imaging tests.