Study suggests some breast cancers may naturally regress
A Norwegian study has raised the possibility that some breast cancers detected by routine screening may have regressed of their own accord if they had not been discovered and treated.
Research published in the Archives of Internal Medicine looked at rates of breast cancer among 119,472 women between the ages of 50 and 64, all of whom were screened three times between 1996 and 2001.
When compared with breast cancer rates in 1992 - when routine breast screening was not available - researchers from the Norwegian Institute of Public Health found that rates of the disease increased significantly following the introduction of routine mammography.
The study authors noted that, if all of these newly detected cancers had developed and been diagnosed over time, there would soon have been a fall in incidence among older women.
However, breast cancer rates among regularly screened women remained higher, suggesting that a small minority of cancers would have spontaneously regressed without treatment.
For every 100,000 screened women there were 1,909 who developed breast cancer during the six-year period, compared with just 1,564 for every 100,000 women in the control group.
The study authors noted that the 'cumulative' incidence of breast cancer remained 22 per cent higher in the screened group, with screened women more likely to have breast cancer at every age.
"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 six years," the researchers wrote.
"This raises the possibility that the natural course of some screen-detected invasive breast cancers is to spontaneously regress."
The scientists conceded that many experts are sceptical about the idea of spontaneous regression, but insisted that the idea merits "careful" consideration, particularly as 32 cases of spontaneous regression of invasive breast cancer were reported in a recent literature review.
"This is a relatively small number given such a common disease. However, as some observers have pointed out, the fact that documented observations are rare does not mean that regression rarely occurs."
Dr Kat Arney, science information officer at Cancer Research UK, said "This work tells us that there is much we still don't understand about the development and progression of breast cancer.
"It also highlights the importance of scientific research for the development of effective breast screening programmes."
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