# 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

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

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.[3]
• In another series, 48% of individuals with cancer had a PSAD >0.15 ng/ml2.[4]
• Differences between races have been noted in one study; in those without prostate cancer:[1]
• 0.19 +/- 0.03 ng/ml2 (blacks).
• 0.11 +/- 0.01 ng/ml2 (whites).

Benson et al.:[6]

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

Where:

${\displaystyle volume={\frac {\pi }{6}}H\times W\times L}$.[8]
H, W, L are the height, width and length.

An alternate estimation of the volume is:

${\displaystyle volume={\frac {1}{2}}D1\times D2\times D3}$.
D1, D2, D3 are the major axes.

Notes:

• The volume of an ellipsoid is:
${\displaystyle {\frac {4}{3}}\pi D1\times D1\times D3}$.
• As 1 cm3 is equal to 1 ml, the units of PSAD are (ng/ml)/cm3 or ng/ml2.

### Immunostain

• Relatively specific for prostate
• May be found in normal pancreatic, salivary gland, Skene's glands and lactating breast tissue.[9]
• 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.