Prostate-specific antigen

Micrograph showing a PSA immunostain marking prostate carcinoma.

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 and follow patients with a history of 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.

Age-normal:

• 40s - 2.5 ng/ml.
• 50s - 3.5 ng/ml.
• 60s - 4.5 ng/ml.
• 70s - 6.5 ng/ml.

Note:

• The units for PSA may also be μg/L; note that 1 μg/L = 1 ng/ml.

Prostate-specific antigen density

Abbreviated PSAD.

Normal is often considered to be: <0.15 ng/ml².

• 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/ml².
• Differences between races have been noted in one study; in those without prostate cancer:
  • 0.19 +/- 0.03 ng/ml² (blacks).
  • 0.11 +/- 0.01 ng/ml² (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.

Notes:

• The volume of an ellipsoid is:

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

• As 1 cm³ is equal to 1 ml, the units of PSAD are (ng/ml)/cm³ or ng/ml².

Free serum PSA/total PSA

Also PSA free-to-total ratio (abbreviated FTR) and PSA free/PSA ratio

• PSA in the serum can be found bound to protein or unbound (free).
• High values of FTR have a lower risk of prostate cancer.
  • Modelling based on a cohort 406 men showed that: FTR ≤0.15 ~46% had prostate cancer versus FTR ≥0.20 ~22% had prostate cancer.

Phoenix definition of biochemical failure

Failure after radiotherapy:

• PSA nadir + 2 ug/L.

Immunostain

• Relatively specific for prostate
• May be found in normal pancreatic, salivary gland, Skene's glands and lactating breast tissue.
• In women, positive in up to 30-40% of breast cancers and also in tubulo-squamous polyps of the vagina.

Microscopic

Features - PSA immunostain:

• Granular cytoplasmic staining.

Notes:

• May be very weak -- need to look at high power.

• 

  Adv Pca - weak PSA - high mag. (WC)

• 

  Adv Pca - weak PSA - very high mag. (WC)

• 

  Adv Pca - PSA - high mag. (WC)

• 

  Adv Pca - PSA - very high mag. (WC)

See also

• Prostate cancer.
• Prostatic-specific acid phosphatase.
• NKX3.1.