Breast cancer screening – debate continues
18 August 2020
Breast cancer is the most common cancer in women and early detection is known to be vital in reducing the death rate. Early breast cancer – a cancer that is contained in the breast or axillary lymph nodes and has not spread to another part of the body – is considered curable. Earlier detection alongside improvements in treatments and therapies can led to an increased chance of cure in ~70–80% of these early breast cancers. One strategy used to detect breast cancers early is through screening, with the aim of ultimately reducing breast cancer specific mortality.
However, one major harm associated with screening is overdiagnosis and its associated consequences, including unnecessary treatments. Overdiagnosis, in this instance, refers to the detection of cancers on screening, which would not have become clinically apparent in the woman's lifetime had she not had screening. Finding the balance between the benefits and risks of screening is a heavily researched area, one aspect of which is to determine whether starting screening from a younger age could lead to better a better balance of benefits and harms.
The screening debate
A recently completed long-term study, the UK Age trial, has found that offering breast cancer screening from age 40 – compared to age 50 as is currently offered – would save one life per 1,000 women screened. Their analysis also showed that overdiagnosis did not increase.
However, the findings from this study are being contested, contributing to an ongoing global debate around the benefits and harms of cancer screening programmes. A 2012 independent review, concluded that overall the UK breast screening programmes conferred significant benefit, saving 1,300 lives each year, and should continue. While the review acknowledged the risk and challenge of overdiagnosis, it stated that these were outweighed by the benefits. These findings were highly debated at the time, and the debate continues with some researchers stating that women are being diagnosed with and treated for cancers that otherwise would not have been detected or caused harm.
The UK Age trial has added to the debate and it is likely it will not resolve the issue over whether to initiate screening at age 40 or 50. Although it showed some benefit in the group screened at age 40, overall there was no reduction in mortality at the end of the 23 year follow up period. In addition some argue that this trial does not reflect current circumstances given that recruitment happened in the late 1990s when mammography and subsequent treatments and therapies may not have been as effective as today.
Most developed nations have mammography screening programmes, however recommendations such as the age range and frequency of screening offered to women differ between organisations and countries, demonstrating a lack of consensus. For example, the European Commission recommends screening between the ages of 45 and 74, whereas Canadian guidelines do not recommend screening for women aged 40–49 years but only ages 50–69. In the UK, breast cancer screening is offered to women between the ages of 50 and 70.
Improving prevention and early detection
Woman are still dying of breast cancer and there is more that can be done to improve prevention and early detection. There is continued research that is improving our ongoing understanding of the variability in breast cancer biology, refining risk prediction, and advancing technologies for early detection and treatments. These efforts are allowing for a greater degree of personalisation, which could also have an impact on screening efforts.
Stratified screening is being explored as a potential approach to refining screening beyond the current ‘one size fits all’ model of screening being available to all women in a certain age range. It aims to match the starting age and frequency of screening to the level of breast cancer risk of the individual. In this scenario information on a range of factors such as genetics, family history, lifestyle, environmental, or reproductive history would be used to estimate an individual’s risk.
At PHG Foundation, we have been examining the implications of scientific progress in breast cancer research for broader prevention efforts, including screening. Our work as part of the Collaborative Oncological Gene-environment Study (COGS) examined the organisational, ethical, legal and social issues in stratified screening for breast cancer and improved risk prediction. As part of the B-CAST consortium we have explored if there are opportunities to improve prevention efforts through personalisation. A policy report exploring issues around personalised prevention will be released in the early autumn. Progress has been made in the research arena - translating this information and findings into clinical care, including screening, is now needed.