On that "regionals are tumors" theme:

"The PSA test measures the blood level of PSA, a protein that is produced by the prostate gland. The higher a man’s PSA level, the more likely it is that he has prostate cancer. However, there are additional reasons for having an elevated PSA level, and some men who have prostate cancer do not have elevated PSA."

Prostate-Specific Antigen (PSA) Test - National Cancer Institute