On Saturday 11 July, 2009, several news outlets, including the Weekend Australian and the Today Show on Saturday, featured stories about the over-diagnosis of breast cancer through mammography screening. The stories arose from a paper published in the British Medical Journal, which claims one in three breast cancers detected through population screening programs is ‘over-diagnosed’.
NBOCC* comment
Mammography screening remains our best method of early detection of breast cancer. Large international trials have shown that mammography screening provides about a 30 per cent reduction in deaths from breast cancer in women aged 50-69 years who participate in regular screening.
The vast majority of breast cancers found through screening would progress if left untreated. However, a small proportion of breast cancers diagnosed through screening may be non-progressive or progress so slowly they would not have caused harm to the woman during her lifetime. This is referred to as ‘over-diagnosis’ and the subsequent treatment of such cancers is referred to as ‘over-treatment’.
Estimates of the size of this sub-set vary widely and are dependent on a range of assumptions. The findings in this paper are at the high-end of international estimates for over-diagnosis and the approach used includes no measures of factors affecting breast cancer incidence other than mammography.
Unfortunately, at this time, we are unable to determine which breast cancers, diagnosed through screening or other means, will progress and which will not. However, research is underway, including molecular and genetic research, to identify this sub-set of cancers and maximise treatment benefits.
This study provides no basis to change current screening recommendations or for women to change their screening practices. However, women should be fully informed about the benefits and potential downsides when making decisions about participating in mammography screening.
Further information can be found in the following Position Statement on Over-diagnosis from mammographic screening.