Overdiagnosis is defined as the histological (i.e. by means of a microscope) diagnosis of a "disease" which, if it had remained unknown, would never have caused any inconvenience to the patient's health during her lifetime, or threatened her life.
It is not a misdiagnosis or a false alarm. It is really cancer in view of its current definition, which is based solely on the diagnosis under the microscope of a sample taken from an organ (the breast) .
The diagnosis is correct but needless to the patient. It is the medical practice that produces this excess of "diseases". Indeed, having cancer cells which were detected does not make the individual as being cancerous. But the more we detect, the more we find.
Its reality is absolutely irrefutable nowadays, its demonstration is based on epidemiological studies with a high level of evidence, it is an accounting reality, wherever screening exists; overdiagnosis is not identifiable at the individual level, because for the concerned individual, or for the doctor who detects the presence of cancerous cells, it is a diagnosis. Overdiagnosis is revealed by comparing populations subjected to different screening intensities.
Which evidence for overdiagnosis of breast cancer?
First of all, several comparative studies, including a fundamental study by the Oslo Institute in 2008 (Zahl P-H, Maehlen J, Welch HG. The natural history of invasive breast cancers detected by screening mammography. Arch Intern Med. 2008 Nov 24;168(21):2311-6).
Two groups of women were compared, one screened every two years, the other examined only once after six years. Result: 22% excess cancers in the screened group. Thus, if all the tumours evolved into perceptible cancers, we should have found the same number of cancers in these two groups of women with the same profile. Since more cancers are found in the group screened every two years, it means that there is an excess of diagnoses.
Autopsy studies further corroborate this result. Almost half of the women (the percentages vary according to age group), who died of causes other than breast cancer, had unexpressed breast lesions. The same phenomenon can also be observed in men in their prostate, which is why systematic screening for prostate cancer is no longer recommended by the High Authority for Health.
The problem with over-diagnosis is that it is accompanied by overtreatment, all without any gain in survival for women, there is no difference in mortality figures between the groups of screened and unscreened women.
However, the presence of more and more diagnoses of breast cancer that would never have manifested themselves, makes it possible to justify the apparently positive results of this health system in the eyes of the promoters of screening and the health authorities.
By detecting "harmless" cancers, screening gives the illusion of contributing to cures. With the overdiagnosis generated, screening makes patients believe that it is effective when they present a cancer that has been proven by microscopic examination, but which will not impact their health (these overdiagnosed cancers remain quiescent, do not progress or progress only slightly or regress).
Thus, by selecting non-ill women, screening justifies a treatment and gives these women the illusion of curing them of a disease they would never have had without it.
Therefore it is the massive screening that generates overdiagnosis and "feeds" on it to convince the medical profession and public opinion of an effectiveness that is not proved.
Overdiagnosis is a source of considerable harm to women who undergo screening mammography. Recognition of the concept of overdiagnosis of cancer by the medical community has been slow, but today it is no longer acceptable to minimize its burden, nor its consequences, and continue to not inform the main interested parties.
Probably in 10 years' time, if we continue in this way, one woman out of six will be diagnosed with breast cancer during her lifetime, perhaps even more since a woman labelled "cancerous" represents herself a family risk factor for her offspring, who will be even more encouraged to be screened. With the certainty that the overall harm induced by screening will only increase…
What are the consequences of overdiagnosis?
The consequences are those of an overtreatment. All lesions, overdiagnosed or not, will be treated.
Women will suffer the consequences of the side effects of treatment. Radiotherapy presents the risk of causing secondary radiation-induced cancers and increases the risk of coronary artery disease by 50% when the left breast is irradiated.
Chemotherapy has known adverse effects on the blood lines, which can lead to nausea, vomiting, hair loss, induced menopause etc…
Hormonal therapy then administered for 4 to 5 years to reduce the risk of recurrence, in the case of hormone-receptor-positive cancers, can be well tolerated, but can also cause fatigue, arthralgia, thromboembolic complications and, in the case of Tamoxifen, increase the risk of endometrial cancer (uterine mucosa).
All of these effects have a profound impact on the emotional, social, professional and economic life of women and on their physical and mental health.
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