A Canadian study tends to show that the risk of dying from breast cancer is no less important in women followed regularly. In France, organized screening greatly reduces mortality.
Breast cancer screening is once again under fire. It is a Canadian study, published this Wednesday in the British Medical Journal (BMJ), which sets fire to the powders. This work, carried out in the early 1980s on nearly 90,000 women aged 40 to 59, followed for 25 years, shows that women who had had annual mammograms for five years were no less likely to die from breast cancer than those who only had a physical exam. After 25 years, 500 deaths had occurred in the 44,925 women followed by mammograms compared with 505 deaths in the 44,910 women in the control group.
The other problem with screening highlighted by this Canadian study is the risk of overdiagnosis. The breast tumors detected were in fact more numerous in the group having benefited from the screening, ie 3,250 in total against 3,133 in the second group at the end of the study.
This “excess” was still 106 tumors after 15 years, which, according to the authors, “means that 22% of cancers diagnosed in the first group were overdiagnosed.” Overdiagnosis here refers to the detection of very small tumors that would not have had an impact during the person’s lifetime.
Can the Canadian results be transposed to France?
Overdiagnosis, no real impact on mortality … These are the perennial criticisms that stick to the skin of systematic screening for breast cancer. However, the relevance of screening is measured above all by reducing mortality. It remains to be seen whether this Canadian study calls into question the French strategy. Several answers can be put forward. First, in Canada, women have been screened from the age of 40, annually, and for barely five years. In France, for ten years, women have been called upon to have mammograms from the age of 50, and this every two years.
50,000 cancers detected per year through organized screening
These differences between France and Canada are not neutral. First of all, the ten years of follow-up make it possible to draw an assessment of organized screening. Each year, in France, a third of the 50,000 new cases of breast cancer are detected thanks to organized screening. In 2012, for example, 16,000 cancers were detected as part of organized screening.
The National Cancer Institute (INCa) estimates that it makes it possible to identify 90% of cancers before the onset of symptoms. This efficiency is explained by the regularity of examinations every two years. And for the Institute, early detection reduces mortality from breast cancer.
“In 2012, according to Inca figures, it fell from 15 to 21%, or 150 to 300 deaths avoided per 100,000 women screened”, reports Dr. Daniel Serin, oncologist at the Sainte-Catherine Institute. (Avignon). Because organized screening is of high quality. It presupposes a systematic second reading of the photographs. Of all the cancers detected, this double reading, specific to organized screening, revealed 6 to 7% last year. It also reduces the risk of over-diagnosis to less than 20%, reports InCa
Listen to Dr Daniel Serin : ” With the exception of this study, all the world studies show that screening makes treatment easier, and less mutilating. The prognosis of tumors is therefore better in the long term… “
Lower reliability of mammography at age 40
Another argument that weighs in favor of French-style screening: before the age of 50, breast density requires radiologists to use a large dose of radiation to obtain a readable image, thus exposing young women to a greater risk of radio-cancer. -induced.
“This is why it is not recommended for women under the age of 50 without a particular risk factor to have screening mammograms”, specifies theInca. The High Authority for Health (HAS) for its part cites very unfavorable estimates with 16 induced cancers for 13 cancers detected per 1000 women between 40 and 44 years old and 27 induced cancers for 24 cancers detected per 1000 women between 45 and 49 years old.
Listen to Dr Daniel Serin: “ Before age 50, the breast is much denser, and mammography does not have the same reliability. When screening before age 50, there are more false negatives and false positives. “
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