It’s not clear what causes prostate cancer. Doctors know that prostate cancer begins when cells in the prostate develop changes in their DNA. A cell’s DNA contains the instructions that tell a cell what to do. The changes tell the cells to grow and divide more rapidly than normal cells do. The abnormal cells continue living, when other cells would die. The accumulating abnormal cells form a tumor that can grow to invade nearby tissue. In time, some abnormal cells can break away and spread (metastasize) to other parts of the body.