Mammography is known to be an imperfect screening tool for detecting breast cancer. Similar to the PSA test for men to detect prostate cancer. According to Wikipedia, mammograms miss cancer (false-negative) in at least 10 per cent of cases, about seven per cent will have a false-positive result which lead to biopsies and other tests. Then there are women who are over diagnosed. That means finding a cancer that does not need treatment.
Let me be clear, mammograms are still worthwhile. They do catch some deadly cancers and save lives. Not all doctors agree with the conclusions in the paper published this November in the New England Journal of Medicine titled, “Effect of Three Decades of Screening Mammography on Breast-Cancer Incidence.”
But the paper is worth discussing. According to Canadian Cancer Society website, breast cancer accounts for over a quarter (28 per cent) of new cancer cases in women. On average, 62 Canadian women will be diagnosed with, and 14 women will die of breast cancer every day.
Researchers looked at 30 years (1976 – 2008) records to examine trends in the incidence of early-stage breast cancer (ductal carcinoma-in-situ and localized disease) and late-stage breast cancer (regional and distant disease) among women 40 years of age or older.
The results of the study indicate that introduction of screening mammography in the U.S. is associated with a doubling in the number of cases of early-stage breast cancer each year, the rate at which women present with late-stage cancer has decreased by eight per cent and only eight of the 122 additional early-stage cancers diagnosed were expected to progress to advanced disease.
The researchers estimated that breast cancer was overdiagnosed in 1.3 million U.S. women in the past 30 years. These cancers would never have led to clinical symptoms. In 2008, breast cancer was overdiagnosed in more than 70,000 women; this accounted for 31 per cent of all breast cancers diagnosed.
Finding breast cancer early does not mean it will always reduce a woman’s chance of dying from breast cancer. This can change if mammograms begin to detect deadly breast cancer before they spread. Once a suspicious area is seen on a mammogram, there is no good way to tell if it is cancer, if it is an early cancer or a deadly one, until patient has had surgery. It would be nice to tell an individual woman whether her cancer needs to be treated just by looking at a mammogram.
That does not mean we stop doing mammograms. Mammograms are still worthwhile, because they do catch some deadly cancers and save lives. Do not stop going for mammograms on the basis of this paper.
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