Participants will be placed into one of two groups by chance. One group will receive a new medicine called pasritamig together with a cancer medicine called docetaxel. The other group will receive docetaxel alone. Everyone will continue their usual hormone treatment unless both testicles have been surgically removed.

People who receive docetaxel alone will also take a steroid medicine called prednisone. People who receive pasritamig will not take prednisone because it may affect how the study medicine works. Both groups will receive medicines before treatment to help reduce side effects.

Researchers will compare the two treatment groups to learn if adding pasritamig can help treat prostate cancer better than standard treatment alone.

People with progressive metastatic hormone resistant prostate cancer.

People can join this study if they are adults with prostate cancer that has spread to other parts of the body and has continued to grow despite hormone treatment. The cancer must be a common type called adenocarcinoma and not certain rarer forms of prostate cancer. Participants must show signs that the cancer is getting worse based on blood tests or imaging scans.

They must continue hormone treatment or have had surgery to remove both testicles, with testosterone levels remaining very low. Participants must have previously received at least one newer hormone treatment for prostate cancer, such as abiraterone, apalutamide, enzalutamide, or darolutamide, and the cancer must have progressed despite that treatment. They cannot have received more than two of these hormone treatments. Researchers are studying whether adding a new medicine called pasritamig to standard treatment can better control advanced prostate cancer.

This study is testing whether adding a new medicine called pasritamig to a standard cancer treatment called docetaxel works better than docetaxel alone for people with advanced prostate cancer that has spread and no longer responds to hormone treatment. Researchers want to learn if the combination treatment can better control the cancer and help people live longer without their cancer getting worse. They will also study how safe the treatment is and what side effects it may cause.