Link to CNN.com article
The U.S. Preventive Services Task Force has reviewed available data about prostate screening and has issued a recommendation that screening using the PSA (prostate-specific antigen test) with or without a rectal exam not be performed.
It sounds counterintuitive at first, but if you look at the evidence, it makes sense. The reason that screening is not recommended is twofold: 1. screening does not lead to a reduction in prostate cancer-related deaths and 2. treatments or tests that are done because of the positive screening tests have negative effects.
The test has a fairly high false positive rate - up to 80% using a certain cut off for serum levels. If a positive test leads to a biopsy, even the biopsy can be read out as cancer, but the cancer may be so slow growing that it would never cause problems for the patient.
Populations that had been screened for PSA were followed for up to 12 years, and the reduction in deaths from prostate cancer were miniscule and statistically insignificant - as low as a 0.03% reduction.
So we have a test with high false positives and no benefit in survival.
On top of that, there are negative aspects to getting a positive test. The patient may have stress and worry over the possibility of cancer, and stress is known to inhibit the immune system and contribute to other diseases. Some men may get biopsies, which can cause a range of side effects from pain to infection to dysfunction. And some men may get their prostates removed, which can lead to complete erectile dysfunction and urinary incontinence. Hormone treatment may involve castration or use of injectable hormones to suppress androgens - basically causing emasculation and possibly contributing to feminization of the patient! All of these are very significant side effects, causing considerable distress to the patient. If the patient would have the same outcome regardless of early screening, and if they potentially have a "cancer" that will never act like a cancer, it does make sense to just not look for it. The patients will have less stress, less side effects, and spend less time under potentially harmful treatment when it is not necessary.
An exception to the "no screening" recommendation is for men that have signs of prostate cancer, and it is unknown if these recommendations hold for men receiving post surgery or treatment screening for recurrence.
More research is obviously needed to find a better test to screen for malignant behaving prostate cancer. RNA microarray analysis of men with malignant prostate cancer is a good place to look. This research is already ongoing, with just this month articles such as this have been published identifying markers associated with outcome.
Link to draft by Preventive Services Task Force
Margaret - are there any equivalent issues in the animal world? And what about the potentially iatrogenic problems caused by treatment of positive psa's in the human world?
ReplyDeleteWe only screen healthy animals for a few diseases. Heartworm is the only one that has a harsh treatment, but the diagnosis is unequivocal and the disease is usually life threatening. I don't think there is a veterinary equivalent, but we are creating more screening tests daily so there might be soon.
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