On 2017 Feb 20, Daniel B Kopans commented:
Response Daniel Corcos' two concerns:
1. Actually, the annual incidence of "true" breast cancers has not been stable. It had been increasing going back to the 1940's. That is the basic point. When women are screened, the cancers detected earlier are layered on top of the increasing baseline. The incidence of invasive breast cancers was increasing in the U.S. and the other countries you mention long before screening became available. .
It is fundamental epidemiology that when screening begins (the prevalence screen) you find the cancers that would have become clinically evident that year PLUS the cancers that were clinically evident that year but over looked PLUS the cancers that are found 1,2, or 3 years earlier by the screening test. Consequently, when new women begin screening the cancers detected (unfortunately called annual incidence) jump up. If this is done in one year (rarely) then it will go up and come down back toward the baseline incidence. If screening continues it never reaches back to the baseline since there will be new women each year having their prevalence screen. In addition, since the incidence of breast cancer increases with age, and screening advances the date of detection (a 47 year old woman will have the incidence of a 49 year old if screening finds cancers 2 years earlier) the annual detection rate will come back down toward the “baseline”, but not reach it. In the U.S. SEER data you can see that the prevalence numbers remained high from the mid 1980’s (when screening began) to 1999 when they turned back down. This is because, in the U.S. the number of women participating in screening steadily increased each year (new prevalence screens) until it plateaued in 1999. This was followed by a decline in the annual detection rate back toward the baseline. However, you will note that the entire SEER curve is tilted up. This is because the baseline was almost certainly increasing by 1% per year over the same time period (as it had been doing going back to 1940). This is why, despite a fairly steady participation in screening after 1999, the annual incidence in 2012 is higher than in 1978. It is not because screening is finding fake cancers, but because the underlying incidence of breast cancer has been steadily increasing. This is evident in other countries as well.
2. Radiation risk to the breast is age related and drops rapidly with increasing age so that by the age of 40 there is no measurable risk at mammographic doses. All of the estimates are extrapolated and even these are below even the smallest benefit from screening. Millions (hundreds of millions??) of mammograms were performed in the 1980’s. If mammography was causing cancers then we would have expected a major spike in breast cancer at the end of the 1990’s (a latency of 8-10 years). Instead, the incidence of breast cancer began to fall in 1999 consistent with the end of the prolonged prevalence peak. Even those who are trying to reduce access to screening no longer point to the radiation risk because there are no data to support it for women ages 40 and over.
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