Spontaneous regression of breast cancer.
|Publication:||Name: Australian Journal of Medical Herbalism Publisher: National Herbalists Association of Australia Audience: Academic Format: Magazine/Journal Subject: Health Copyright: COPYRIGHT 2008 National Herbalists Association of Australia ISSN: 1033-8330|
|Issue:||Date: Winter, 2008 Source Volume: 20 Source Issue: 4|
Zahl PH, Maehlen J, Welch HG. 2008. The natural history of invasive
breast cancers detected by screening mammography. Arch Int Med
Researchers from this study suspect that up to one fifth of breast cancer may spontaneously regress if left alone. The discovery was made by accident while they were researching the effects of regular mammogram screening. They compared cumulative breast cancer incidence in age-matched cohorts of women residing in 4 Norwegian counties before and after the initiation of biennial mammography, which started in 1996.
The screened group included all women who were invited for all 3 rounds of screening during the period 1996 through 2001 (age range in 1996, 50-64 years). The control group included all women who would have been invited for screening if there had been a screening program during the period 1992 through 1997 (age range in 1992, 50-64 years). All participants were invited to undergo a one-time screening to assess breast cancer prevalence at the end of their observation period. Screening attendance was similar in both groups (screened 78.3%, controls 79.5%).
As expected the cumulative incidence of invasive breast cancer was significantly higher in the screened group than in the controls. But when the controls had their one-time mammogram six years later, in many cases the cancer that had been detected at the beginning of the study had gone. Overall the cancer rate was 22% higher in the women who were regularly screened.
Even after prevalence screening in controls, (4-year cumulative incidence 1268 vs 810 per 100,000 population; relative rate 1.57; 95% confidence interval 1.44-1.70), the cumulative incidence of invasive breast cancer remained 22% higher in the screened group (6-year cumulative incidence 1909 vs 1564 per 100,000 population; relative rate 1.22; 95% confidence interval, 1.16-1.30).
Because the cumulative incidence among controls never reached that of the screened group, it appears that some breast cancers detected by repeated mammographic screening would not persist to be detectable by a single mammogram at the end of 6 years. The most likely possible explanation for this, according to the researchers, is that the natural course of some screen detected invasive breast cancers is to spontaneously regress.
As the researchers point out, medical ethics does not allow cancer to follow its natural path without intervention and so there is very little evidence of this phenomenon. Nonetheless there are many individual cases of cancers that naturally regress, and this is recognised as a possible outcome of cases of metastatic melanoma and metastatic renal cell carcinoma in particular.
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