This study begins with a screening period that lasts about 28 days to see if a person can join. If eligible, participants will receive a study medicine called JANX014. This is a new immune based drug that is given through a vein at a clinic or hospital. The medicine may be given once every week, every two weeks, or every three weeks, depending on the study group and safety results. The study has two parts. In the first part, small groups receive different dose levels to find a safe amount of the medicine. In the second part, more people receive selected doses to learn more about safety and early effects. During the study, participants will have regular visits that include physical exams, blood and urine tests, heart tests, and imaging scans such as CT or PET scans. Some early treatment visits may require short hospital stays so doctors can watch closely. Participants may also check their temperature and blood pressure at home.

This study enrolls adult men with metastatic castration-resistant prostate cancer.

This study is for adult men who are 18 years old or older and have advanced prostate cancer. The cancer has spread to other parts of the body and is no longer responding to standard treatments like hormone therapy. Men must be healthy enough overall, with organs working well based on doctor exams and blood tests, to safely take part in the study.

The purpose of this study is to find out if a new medicine called JANX014 is safe for people to use. Researchers want to learn how the body reacts to this medicine and how it affects the immune system. They also want to see if the medicine shows early signs of helping control prostate cancer. What doctors learn from this study may help create better cancer treatments in the future.