May 18th, 2011
06:00 PM ET
For men being screened for prostate cancer, the results of a PSA test can become mired in confusing caveats. The test measures the level of a protein called prostate-specific antigen in a man’s blood. A positive test may indicate the presence of a virulent form of the disease, or not, since PSA tests are not sensitive enough to distinguish between deadly cancers and those that would never kill the patient. All of that makes deciding how to interpret PSA tests difficult.
A new study may add some much-needed clarity to that process.
A large Swedish study found that men with the highest PSA levels between ages 44 and 50 were most likely to die or develop metastatic prostate cancer 30 years later. Conversely, men whose PSA levels were lower were less likely to die or develop metastatic disease.
Researchers analyzed blood samples from about 12,000 men in Sweden. The blood samples were tested for the presence of PSA at three ages - 44 to 50, 51 to 55, and at 60 - and grouped them based on highest and lowest levels.
"Forty-four percent of prostate cancer deaths occurred in men who had the top 10 percent of PSA levels when they were tested between the ages of 44 and 50," according to a study abstract that will be presented next month at the American Society of Clinical Oncology annual meeting.
"What that means is if you're 45 and you have a very low PSA, the chances you're going to develop the kind of prostate cancer that kills is very small," said Dr. Otis Brawley, chief medical officer of the American Cancer Society and CNNHealth.com expert doctor. "That's separate from saying that the chances you'll develop prostate cancer are small. The chances that you'll develop the kind that kills are small."
It is an important distinction, said Brawley.
"We have data to suggest that 60% of guys we cured of localized prostate cancer never needed to be cured and the worst thing we could have done was telling them they had prostate cancer," said Brawley.
Studies that replicate this one may eventually allow doctors to parse out which cancers will develop into serious ones, resulting in more aggressive screening for men with high PSA levels, and fewer screenings for men with lower levels.
Dr. George Sledge, president of the oncology doctors association, said this study suggests, if you have a low PSA, you may need only three PSA tests during your lifetime.
Prostate cancer screening has been muddled by controversy, in part because the test detects cancers that most likely would not have spread or killed the patient. The consequences of treating a relatively innocuous cancer are serious - infection, erectile dysfunction, bowel damage, and incontinence.
Contrary to the confusion surrounding prostate cancer screening, cervical cancer guidelines are becoming clearer. According to a large Kaiser Permanente study, most women can safely opt out of the yearly cervical cancer screening, instead getting tested every three years.
"For the time being, women should get a Pap test every three years if they've had three normal yearly Pap tests in the past, and they might want to get HPV testing, which might make things even safer," said Brawley.
Safer, perhaps, because according to the Kaiser study, testing for HPV may be a more accurate predictor than a Pap test for whether a woman will develop cervical cancer.
Researchers followed 331,818 women who had Pap tests, HPV tests, or both. After comparing the two tests, researchers found that a positive HPV test was more predictive of cervical cancer than a positive Pap. Same goes for a negative test. Women who had an HPV-negative test were less likely to develop cancer than women with a normal (or negative) Pap test.
According to the study abstract, "In routine clinical practice, a single HPV test was clearly superior to a single Pap smear for predicting who would develop... cancer within 5 years."
As a result, an HPV test could provide the best barometer for the presence of cancer, so women who get a negative HPV test might need less frequent cervical cancer screening.
Lead study author Hormuzd A. Katki of the National Cancer Institute said instead of getting both an HPV test and a Pap smear, women should be given an HPV test first. If it is negative, the Pap smear can be safely skipped.
"Pap testing should only be reserved for HPV-positive women," said Katki.
The bigger question is whether this study makes the Pap test obsolete? Not really, say study authors, but it may mean that HPV tests could soon be a bigger part of the routine at the doctor's office.
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Get a behind-the-scenes look at the latest stories from CNN Chief Medical Correspondent, Dr. Sanjay Gupta, Senior Medical Correspondent Elizabeth Cohen and the CNN Medical Unit producers. They'll share news and views on health and medical trends - info that will help you take better care of yourself and the people you love.