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BLOG: June 2010 - December 2013
II - Mammography
7. Mammography benefits
During the 1980-ties, screening healthy women for breast cancer (BC) with X-ray mammography became part of the U.S. public health policy on the grounds of its proven ability to detect suspicious growth at an earlier stage - in general, before it becomes symptomatic. At that time, large uncontrolled public trial (Breast Cancer Detection Demonstration Project, 1973-80), as well as the first large randomized controlled trial (Health Insurance Plan of Greater New York, HIP, 1971), seemingly confirmed the expected benefit: reduction in breast cancer mortality (BCM) in the screened population.
Additional benefit, assumed and widely advertised despite never being documented in trials, was generally less aggressive treatment of the screened population, due to breast cancer being generally detected at an earlier stage.
These are the three major benefits associated with the
preventive screening mammography, ever since it was introduced in the U.S.
nearly three decades ago:
Of the three,
only the first, earlier detection, has withstood closer scrutiny.
However, by itself it does not represent a benefit, unless it translates into lower mortality and/or less invasive treatment.
For decades, screening establishment was advertising significant BC mortality reduction due to the screening. This view, however, was based on the two trials with the most favorable outcome for the screening (HIP and Two County), while
neglecting trials reporting
no significant effect,
Within past decade, systematic reviews of all relevant trials made this loudly advertised significant reduction in BC mortality in the screened populations shrink to marginal, to the point that
it cannot be said with certainty whether such benefit really exists, or it was created by poorly designed and/or biased trials and random deviations within trial populations.
Most researchers still tend to believe that screening does result in a relatively small, not entirely insignificant reduction in breast cancer mortality.
Not so with the proclaimed benefit of less aggressive treatment. The same systematic reviews of breast cancer trials (#5, #9), as well as data from the actual screening programs, revealed that the screened population had been subjected to generally more treatment, mainly due to the higher number of detected/diagnosed cancers. Since significant number of these breast cancers are pseudo-disease, i.e. abnormal growths that would not evolve into a symptomatic cancer during lifetime, the excess treatment of the screened populations is not justified.
In other words,
screening results in more, not less treatment, which makes it not beneficial, but more risky in this respect.
In addition, there are solid indications that the screened population may not have lower total (all-cause) mortality; in fact, it may be higher, possibly significantly so. If that is true, both earlier detection and possible small breast cancer mortality reduction due to mammography screening would have been dwarfed by that one harm alone. And the rest of them is already enough to this form of screening unjustified and unattractive for the average women.
Following pages look in more details at that one remaining benefit of screening, the earlier detection. Is it a benefit at all? In addition, will tackle the most disturbing unanswered question about screening mammography: is already statistically near-negligible reduction in BC mortality due to preventive screening further diminished, offset, or even exceeded by the higher total mortality rate among the screened population?