An overview of the expected benefits of breast cancer screening

The goal of screening is to detect breast cancer early, before it spreads throughout the body. 3 benefits can be expected :
- a reduction in mortality from breast cancer
- an increase in life expectancy
- a reduction in treatment.

Reduction in breast cancer mortality

Screening advocates claim that screening reduces breast cancer mortality by 20%. This claim is primarily based on meta-analyses of 11 randomized clinical trials conducted between the 1970s and 1980s.

This statement, however, is not universally accepted.
On the one hand, the meta-analyses concluding to this 20% decrease have been contested.
On the other hand, these 11 randomized clinical trials date back more than 30 years, and breast cancer treatments have evolved significantly since then. However, the value of early detection, and thus the potential value of screening, is dependent on the effectiveness of cancer treatments.
To be convinced of this, consider the following situation: all small tumors have been cured, but we are completely helpless in the face of advanced tumors. It is obvious that, in this case, an early diagnosis, prior to the stage of advanced tumor, is critical. This is the situation in which screening could be of maximum benefit.
Now imagine this other situation: all tumors, even the most advanced, are easily cured. In this case, early detection is of little interest because all tumors, whether advanced or not, have the same good prognosis. Screening is therefore pointless in this situation.
Of course, these are virtual extremes, and in the 1970s and 1980s, we were somewhere in the middle, as shown in the diagram below.
And, thanks to therapeutic advances, we're probably closer to the right now, with less benefit from screening.

Recent studies even suggest that screening would not result in a significant reduction in mortality ( Autier et al. 2017 Autier P., Boniol M., Koechlin A., Pizot C, Boniol M.
Effectiveness of and overdiagnosis from mammography screening in the Netherlands: population based study.
BMJ 2017;359. doi:10.1136/bmj.j5224 , Møller et al. 2018 Møller M.H., Lousdal M.L., Kristiansen I.S., Støvring H. (2018)
Effect of organized mammography screening on breast cancer mortality: A population based cohort study in Norway.
Int J Cancer. doi:10.1002/ijc.31832 ). Even if these non-randomized studies do not allow us to assert that screening is ineffective, they at least confirm that the 20% reduction in mortality seen in the 1970s and 1980s may no longer be relevant.

Increased life expectancy

No study has been able to demonstrate that screening for breast cancer increases life expectancy.

This information is critical for a woman who is questioning whether or not to participate in screening. Clearly, the goal of screening is to increase life expectancy in good health, not to replace deaths from breast cancer with deaths from heart attacks or strokes.

The lack of studies demonstrating an increase in life expectancy with screening can be explained in two ways.
First, there is an increase in life expectancy, but it is too small to be demonstrated.
Breast cancer deaths account for only 4% of all deaths in women, with 12,000 deaths per year out of a total of 300,000 deaths.
Even if screening reduced breast cancer mortality by 20% (i.e., avoided 2,400 deaths), it would only reduce overall mortality by less than 1%. It is difficult to demonstrate such a small reduction.
Second, if there is no evidence of an increase in life expectancy, it is because there is none.
Screening leads to over-diagnosis (see page on the risks of screening). These over-diagnoses lead to unnecessary treatments (= over-treatment). These treatments are unnecessary, yet they are not without side effects, some of which can be serious or even fatal. As a result, the benefit of lowering breast cancer mortality may be offset by an increase in mortality from other causes related to the side effects of overdiagnosis treatments.

On the other hand, it should be remembered that the increase in life expectancy is the result of a policy of small steps: beating cancer mortality, cardiovascular disease mortality, neurodegenerative disease mortality, and so on. Reducing breast cancer mortality remains of interest within the context of this policy of small steps, even if it does not result in an increase in women's life expectancy on its own.

Reduced treatment

Screening supporters claim that screening reduces the breast cancer treatment, but they provide no data to back up this claim.
There is limited data regarding chemotherapy and radiation.
PMSI (program for the medicalization of information systems) data, on the other hand, allow us to track the number of surgical treatments for breast cancer. And the data are unmistakable: from 2000 to 2016, the number of mastectomies in France increased steadily, with no impact from screening. The graph below, from Robert et al. 2017 Robert V., Doubovetzky J., Lexa A., Nicot P., Bour C.
Le dépistage organisé permet-il réellement d’alléger le traitement chirurgical des cancers du sein ?
Médecine 2017;13(8):367-371. doi:10.1684/med.2017.233 , shows the annual progression of the number of total mastectomies for breast cancer in France.

In summary :
- No proven benefit in terms of life expectancy
- A reduction in breast cancer mortality that is disputed,
        with, on the one hand, randomized controlled studies that are too old and conclude that there is a 20% reduction in mortality,
        and on the other hand, recent but non-randomized studies, which do not show a reduction in mortality.
- No reduction in surgical treatments and no evidence regarding radiotherapy and chemotherapy.

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Dernière mise à jour le 15/09/2021