NEW YORK--The identification of prostate-specific antigen immunoreactivity (IR-PSA) in some cases of breast cancer has raised the possibility that PSA could be used as a biochemical marker for prognosis of breast cancer.
Speaking at the International Conference on Human Tumor Markers, He Yu, a doctoral candidate in clinical biochemistry at the University of Toronto, reported that IR-PSA was detected in 30% of tumor cytosols taken from 1,200 women with primary breast cancer.
Although PSA was initially thought to be produced exclusively by the prostate, Mr. Yu said that it can be detected in low levels in the periurethral, perianal, salivary, and sweat glands.
Using a time-resolved immunoflu-orometric assay to measure extremely low levels of PSA, the Toronto team was surprised to find IR-PSA in breast cancer tissue, but repeated testing yielded the same results.
"The PSA found in the breast cancer tissue was identical to that found in the prostate," he said. He added that normal breast tissue is also capable of producing PSA under conditions of steroid hormone stimulation, eg, with use of oral contraceptives. Fluid secreted from the breast, such as milk and cystic fluid, also contains IR-PSA.
Preliminary clinical studies indicate that PSA-positive breast cancer is associated with the presence of steroid hormone receptors, younger patient age, and earlier clinical stage.
Survival analysis suggests that patients with PSA-positive breast cancer may have longer relapse-free survival than do those with PSA-negative disease. Mr. Yu concluded that PSA may, therefore, have value as an independent prognostic marker for breast cancer.