Study Faults Standard Prostate Cancer Test
BOSTON — A new study has found that 15% of older men with supposedly normal readings on the widely used PSA test have prostate cancer -- and some even have aggressive tumors.
The findings intensify the difficulty of how to interpret the test results and how vigorously to treat men with no symptoms.
Some experts think the threshold for what constitutes normal on the PSA test should be lowered, at least in some cases. But others say that could lead to more unnecessary operations in the many men whose tumors are so slow-growing that something else will kill them before cancer does.
“It’s a very powerful test, but it’s not perfect,” Dr. Leonard Gomella, a urologist at Jefferson Medical College in Philadelphia.
Sixteen percent of American men can expect to be diagnosed with prostate cancer at some point. Yet most such tumors grow slowly, with the death risk at just 3%. Screening methods cannot always establish whether cancer is present and dangerous, so some cases are missed and others are overtreated with surgery or radiation.
The study, conducted with the help of funding and personnel from the National Cancer Institute, appears in today’s New England Journal of Medicine.
It focuses on the standard screening test for prostate cancer: the prostate-specific antigen test, or PSA count. That blood test has been used on millions of men since the late 1980s to screen those with no symptoms. Many start screening at age 50.
The test measures bloodstream levels of a protein manufactured by the prostate, a male sex gland. Cancer expands the gland, pumping out more of the protein and raising the PSA count. A count of 4 or below (calculated in nanograms per milliliter) has been widely considered to be normal.
But the researchers found that 15% of 2,950 men ages 62 to 91 had normal PSA counts and rectal exams, yet had prostate cancer. And 2% of the overall group had tumors that looked aggressive under a microscope.
“This study adds to information that perhaps the PSA threshold may be dropped to 2.5 or so,” Gomella said. “The number 4 may not be the ‘normal’ that we look at anymore.”
