For every advanced stage cancer detected through screening among 70-75-year-olds, around 20 "overdiagnosed" early stage cancers were detected.
As people in Western societies are living longer, it is expected that in the coming years there will be an increase in the proportion of older women with breast cancer - the largest contributor to death from cancer in women worldwide.
Older women with breast cancer are at increased risk for adverse outcomes and side effects from breast cancer treatment, and studies have shown that risk of death from breast cancer increases with age.
Although doctors have assumed that screening programs could diagnose breast cancer at an earlier stage in older women and therefore improve prognosis, no strong evidence exists for the benefits of this.
However, although some guidelines recommend breast cancer screening with mammography for women up until the age of 75, randomized trials investigating the success of these guidelines have rarely included women over the age of 60.
Netherlands guidelines recommend screening up to age 75
To further investigate the benefit of screening programs for older women, Dutch researchers assessed the available evidence for the national breast cancer screening program in the Netherlands. In this program, the upper age limit for screening was extended from 69 to 75 in 1998, with national guidelines recommending screening women up to the age of 75.
The team, from Leiden University Medical Centre, analyzed data from the Netherlands Cancer Registry. They tracked all new cases - 25,000 in all - of invasive and non-invasive (in situ) breast cancer among women aged 70-75 during the period 1995-2011.
In addition, 13,000 women aged 76-80 were also included in the study, so the researchers could examine any changes in breast cancer incidence among women who were too old to be eligible for the national screening program.
The data showed a sharp rise in new cases of early stage breast cancer among women aged 70-75 after the national screening program was introduced. The increase was from 248.7 cases per 100,000 women before the program was introduced, to 362.9 diagnosed cases per 100,000 women after it was introduced.
For advanced breast cancer, though, there was a small but significant decrease in the number of diagnosed cases - 58.6 cases before, and 51.8 cases per 100,000 women after, the program was introduced.
In the sub-group of older women aged 76-80, the number of new cases of advanced breast cancer did not change, but new cases of early stage cancer fell slightly.
In their analysis - which is published in the BMJ - the researchers suggest that for every advanced stage cancer detected through screening among 70-75-year-olds, around 20 "overdiagnosed" early stage cancers were detected. According to the authors, these "extra" cases amount to "a considerable proportion."
Why is overdiagnosis a problem?
Why overdiagnosis is a concern, the researchers explain, is because overtreatment can undermine quality of life, exposing vulnerable older people to the side effects of breast cancer treatment. Also, the authors warn, for little obvious health benefit, there is "a potentially hefty price tag."
The authors state:
"Instead of using mass screening, the decision to participate in the screening program should be personalized, based on remaining life expectancy, breast cancer risk, functional status and patients' preferences."
This was a detailed analysis following a large number of participants over a long period of time. However, the researchers say that one limitation of the research may be that the length of follow-up after implementation of the screening program may not have been long enough to result in a decreased incidence of advanced tumors.