Prostate-specific antigen

The prostate gland and its surrounding structures. (WC/NCI)

Prostate specific antigen, abbreviated PSA, is marker that is quite specific for the prostate.

General

• Quantity in the serum used to screen for prostate cancer.
• PSA immunostain useful for classifying a carcinoma as prostate carcinoma.

Serum PSA

• Normal - typically <= 4.0 ng/mL.
  • Sensitivity: 82% (whites), 90% (blacks).
  • Specificity: 52% (whites), 38% (blacks).
• Increases with age.

Prostate specific antigen density

Abbreviated PSAD.

Normal is often considered to be: <0.15 ng/ml.

• Approximately 8% of individuals below the cut-point (0.15 ng/ml) have medium or high-grade cancer.
• In another series, 48% of individuals with cancer had a PSAD >0.15 ng/ml.
• Differences between races have been noted in one study; in those without prostate cancer:
  • 0.19 +/- 0.03 ng/ml (blacks).
  • 0.11 +/- 0.01 ng/ml (whites).

PSAD is a better predictor than (unadjusted) serum PSA for:

• Gleason score upgrading on prostatectomy.
• Benign prostate gland versus prostate cancer.

A forumla for PSAD

Benson et al.:

$PASD={\frac {serumPSA}{volume}}$

Where:

$volume={\frac {\pi }{6}}H\times W\times L$.

H, W, L are the height, width and length.

An alternate estimation of the volume is:

$volume={\frac {1}{2}}D1\times D2\times D3$.

D1, D2, D3 are the major axes.

Note:

• The volume of an ellipsoid is:

${\frac {4}{3}}\pi D1\times D1\times D3$.

See also

• Prostate cancer.