Prostate specific antigen (PSA)

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Prostate specific antigen (PSA) is currently used as a tumor marker for prostate adenocarcinoma.

PSA is a 33 kilodalton glycoprotein produced in prostate epithelial cells. Its normal physiologic role is as a liquefying agent for seminal fluid; only a tiny amount leaks into the blood, therefore its normal serum level is usually very low. Elevated serum levels of PSA have been associated with prostate carcinoma.

Prostate specific antigen can exist in the serum in two forms:

  • bound/complexed (to serum protein): elevated levels are associated with prostate cancer
  • free PSA (fPSA): elevated levels are associated with benign prostatic hyperplasia (BPH)

PSA levels

Although an increased PSA level is associated with prostate cancer, a low level cannot exclude prostate cancer. Although exact cut-off values are continually in flux, subject to the most recent data:

  • 2-4 ng/mL: 15-25% change in a man >50 years old of having prostate cancer
  • 4-10 ng/mL: imaging screening/biopsy indicated

The absolute level may also be misleading if there is a trend in the data upward (or downward) over time. Men with enlarged glands from benign prostatic hyperplasia may also have elevated PSA levels. False-positive levels have been associated with:

An upward trend in a patient's PSA value is usually concerning after a prostatectomy, raising suspicion for recurrent/metastatic disease.

Long term (> 6-12 months) treatment with 5α-reductase inhibitors (e.g. finasteride, dutasteride) tends to reduce the PSA level by about 50% .

PSA in women

Prostate specific antigen was at one time thought to be only secreted from the prostate, but it is now clear that it is also secreted by cells in women, in particular the breast. The normal serum PSA level in females is approximately 1,000 times less than in men .

PSA is synthesized by both healthy and pathological breast tissue, and studies suggest that an elevated serum PSA, may point towards a favorable prognosis in breast cancer and be useful in monitoring treatment response .

See also