PSA or Prostate Specific Antigen, is a protein that is produced mainly by the cells in the Prostate. The prostate is a small gland in men that surrounds the urethra and produces a fluid that makes up part of semen. Most of the PSA that is produced by the Prostate Gland is released into the fluid but some of it enter the blood stream. The IHC (immunohistochemistry) test is conducted to find the amount of PSA in the blood. The PSA test helps to monitor and screen prostate cancer in men.