Prostate Cancer Tests May Get More Precise
By Tim Friend, USA TODAY

July 16, 2003

Scientists have discovered variations in a gene that controls levels of prostate specific antigen (PSA) in men — a finding that could make PSA screenings for prostate cancer more accurate.

Scientists had assumed that levels of PSA are tied directly to the degree of disease in the prostate gland. PSA levels have been shown to increase when cancer develops, when prostate glands become enlarged and when prostates are irritated, which can occur from lack of sexual activity.

But a study out today in the Journal of the National Cancer Institute shows that gene variations, called single nucleotide polymorphisms, can directly influence levels of PSA that can be detected in a man's bloodstream, says Scott D. Cramer of Wake Forest University Baptist Medical Center in Winston-Salem, N.C. Depending on the type of variation, the biological marker can be higher or lower than normal.

Cramer says it's too early to know whether men with higher levels are at higher risk for cancer, or whether some men may simply have higher levels without being at risk. It is also too soon to know whether men with lower-than-normal PSA levels are at risk of having their cancer go underdiagnosed.

The researchers analyzed blood samples from 405 white males who already were part of a study of asbestos exposure.

William Catalona, the physician who was the first to demonstrate that PSA levels can be used to screen for prostate cancer, said the study will yield important information about PSA testing in the near future.

"This study shows for the first time that PSA levels are somewhat controlled by genes inherited from a parent," said Catalona, of the Northwestern Memorial Hospital in Chicago. He expects that increased PSA levels caused by the gene variation will correspond with an increase in risk for cancer.