Understanding screening mammography

Understanding The Concept Of Screening

Screening mammography involves x-raying an entire healthy population of women with no breast symptoms with the aim of detecting cancers before they are big enough to feel.

Conceptually screening is a calculated gamble that benefits only a few of the participants.

If you are one of the 10% of women destined to get breast cancer then a screening mammogram may detect it at an early stage where optimal treatment may reduce your risk of dying.

If, however you are one of the 90% of women who is never going to get breast cancer then screening will in hindsight have involved unnecessary x-rays for more than 25 years of your life. Along the way there is a reasonable chance that you will end up having extra tests including needle biopsies or even surgery to investigate changes that turn out to be non-cancerous. Unfortunately we do not have a crystal ball to predict which group you will fall into as the majority of women who develop breast cancer have no identifiable risk factors.

What is the difference between a diagnostic and a screening mammogram?

Diagnostic tests are used to assess a specific problem such as a lump, and in this setting a mammogram often forms an integral part of the Triple Assessment process.

This is in contrast to a screening mammogram that is performed on well women with no breast symptoms.

What Can You Expect From Screening Mammography?

Advocates of screening claim the following benefits:

45% reduction in risk of dying from breast cancer in a screened population aged 65 - 69 years.

30% reduction for women aged 50 - 65 years.

20% reduction for women aged 45 - 49 years.

If this is correct an average 30% reduction in mortality might translate into a reduction in the annual mortality in New Zealand from 600 deaths to about 400 deaths due to breast cancer. These figures came from trials and we cannot be sure that the benefits are sustained in a less optimised "real world" situation such as that in New Zealand at present.

The Need For Clear Information On Screening Mammograms

Breast cancer is seen as a major health problem in New Zealand.

It is claimed that finding and treating cancers at an early stage may result in better survival hence the slogan "early detection is your best protection"

Mammographic screening is percieved to be the best way to achieve this goal and there are widely publicised campaigns to spread the message that a mammogram may save your life. Calls for extensions to screening continue. One might be forgiven for concluding that we could beat breast cancer completely if we could get all elligible women to have regular mammograms.

To promote attendance information is often presented in a manner biased in favour of mammograms.Women consequently overestimate what mammograms can achieve and are often not aware of the limitations and associated risks. These unrealistic expectations can result in disappointment, anger and a sense of betrayal when breast cancer develops despite regular mammograms, sometimes over many years.

Women need to be provided with accurate information on the risks and benefits of mammographic screening to allow them to make an informed choice as to whether they wish to participate in this form of screening. This advice should also include information on lifestyle factors that can reduce breast cancer risk and improve overall well-being.