By Robert Bazell
Chief Science and Medical Correspondent
Women who have received a “false positive” on a mammogram may have new cause for worry, according to a study released Thursday.
A false positive occurs when a radiologist detects an abnormality in a mammogram – that is, there is some apparent growth that is checked out, usually with a needle biopsy -- but it is determined there is no cancer. The research from the University of Copenhagen found that women who have been given additional testing because of a false positive run a 67 percent greater risk of a breast cancer diagnosis in the future. Experts say the result from the records of 58,000 women in Denmark is not cause for alarm. But it is a warning for those who have gotten a false positive to be more vigilant.
False positives may just be an artifact that appears on the mammogram, but they also include abnormally growing cells classified as atypia, papilloma or lobular carcinoma in situ. These are not cancer and they don’t require treatment, but women with these growths “have a 25 to 33 percent lifetime chance of developing breast cancer versus 11 percent in the general population,”according to Dr. David Dershaw, head of breast imaging at Memorial Sloan Kettering Cancer Center in New York. So, any woman who has a false positive should consider a conversation with her doctor about whether she needs more frequent checkups or screening with higher resolution technology such as MRI.
There were further questions about mammograms in a large study released Monday, where researchers followed the records of almost 40,000 women in Norway. Because that country phased in regular mammography from 1996 to 2005, the researchers were able to look at the effects before and after regular screening. The study leaves no doubt that the screening is saving lives. But it found that between 15 and 25 percent of the women diagnosed with breast cancer would have lived to die of some other cause and thus did not need treatment.
Such “overdiagnosis,” as the study authors including some the Harvard School of Public Health characterize it, is inevitable with any cancer screening test. Some cancers can kill. Others never do. But as Dershaw puts it “until it is possible to differentiate which are bad and which are not, all need to be treated.”
The extent and potential harm of overdiagnosis make up almost all of the arguments about cancer screening tests. For some tests such as colonoscopies or pap tests the removal of abnormal growths that could become cancer subjects the patient to relatively little risk or discomfort. The PSA screening test for prostate leads so many men to harsh treatments they often do not need that many question its usefulness.
Most experts believe the overdiagnosis from mammography – especially for women 50 and older— is well worth it for the lives saved.
But one of the reasons why there is such continuing debate about the screening test is that it is far from ideal. Not only does it find cancers that will never be dangerous it can often miss ones that go on to be life threatening.
Many medical and activists groups have pushed hard to get more women screened with mammography. That is a noble goal. But it is a mistake to think that is the solution to the great public health threat of breast cancer
Some of the most hopeful breast cancer research is a search for a blood test or other reliable method of detecting breast cancer early, especially the life threatening forms. MRIs find more but also are so expensive and find so many false, that most doctors say they should be reserved for women at very high risk.
Neither study is an argument for women to avoid regular mammograms. Until scientists achieve the goal of finding a more reliable and cost effective test, it is the best breast cancer screening tool available.
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