What is the problem ?

As we can see, screening results are not as satisfactory as we might have hoped. So, what's the problem with screening ?
To understand this, we must remember that there is not a single breast cancer, but rather different types of breast cancer, each with its own evolutionary patterns. Some cancers progress quickly, others slowly, and still others do not progress at all or even regress spontaneously.
These variations in progression are critical in determining the benefits /risks balance of screening.
It is important to remember that a tumor can only be detected by screening if the screening mammogram is performed within a "window" of time between when the tumor is large enough to be seen on mammography and when the tumor is large enough to cause symptoms (screening is then unnecessary; it is the symptoms that lead to the diagnosis).
The window for screening is short for rapidly progressive tumors and long for slowly progressive tumors, as shown in the diagram below. As a result, screening is inherently ineffective for rapidly progressing tumors (invitation for screening may arrive too soon or too late) and significantly more effective for slowly progressing tumors (if the tumor is missed by a first screening, the window is long enough to allow finding it 2 years later, during the next screening).
Unfortunately, these rapidly progressing tumors should be found in priority because they have the worst prognosis and every day counts.
The benefit of screening for slowly progressing tumors is much less obvious. If the progression is very slow, these are often over-diagnosed, and even if they are not, gaining a few months will not change the prognosis significantly.

It can be seen that screening has a structural flaw that leads it to tend to miss its target, the rapidly progressing tumors with a poor prognosis, and to create overdiagnoses.

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Dernière mise à jour le 12/09/2021