A prostate cancer stage defined by the Jewett staging system. Stage B prostate cancer is cancer that began in the prostate and is more advanced than stage A, but has not spread outside the prostate. Stage B is divided into stages B0, B1, and B2. In stage B0, the cancer is detected only by increased blood levels of PSA (prostate-specific antigen). In stage B1, cancer is in one area of one lobe of the prostate. In stage B2, there is more cancer in one or both lobes of the prostate.