Screening Mammography Information–DETAILED

In this section I am including a table from the article discussed in the “Comprehensive” section, which lists some “facts” that are important in making a decision about screening mammography.

Mammography Is Not a Perfect Screening Test,
and Understanding of Its Benefits and Harms Is Incomplete

  • Some cancers will be missed, and some women will die of breast cancer regardless of whether they are screened
  • Many cancers will be found, but most women diagnosed with breast cancer will be cured regardless of whether the cancer was found by a mammogram.
  • Some cancers that are found would have never caused problems. This is called “overdiagnosis.” Often, women are called back for further testing because of an abnormality that is not cancer; this is called a “false-positive” result.
  • Studies of the benefits and harms of mammography have limitations and inconsistent results. The numbers reported below are estimates based on what most experts consider the best available evidence, but uncertainty about these estimates remains.

Benefits of Mammography

  • Mammography decreases the number of women who will die from breast cancer. This benefit is greater for women who are at higher risk for breast cancer based on older age or other risk factors such as family history.
  • The number of women whose lives are saved because of mammography varies by age. For every 10 000 women who get regular mammograms for the next 10 years, the number whose lives will be saved because of the mammogram by age group is approximately

5 of 10 000 women aged 40 to 49 years
10 of 10 000 women aged 50 to 59 years
42 of 10 000 women aged 60 to 69 years

  • If your breast cancer risk is higher than average, you may benefit more from a mammogram than someone with average risk.

Harms of Mammography

  • About half or more of women who have a mammogram yearly for 10 years will have a false-positive mammogram, and up to 20% of these women will need a biopsy. If you do decide to have a mammogram, you can anticipate that you will have at least 1 false-positive finding for which you are called back for additional images and perhaps a biopsy. Most of these findings are false alarms.
  • For some women undergoing regular screening, the mammogram may find an invasive cancer or noninvasive condition (ie, ductal carcinoma in situ) that would never have caused problems (“overdiagnosis”). We cannot tell which these are, so they will be treated just like all other cancers. Experts are uncertain of how frequently this happens, but estimates suggest that if a woman undergoing a screening mammogram is diagnosed with cancer or ductal carcinoma in situ, there is about a 19% chance that the cancer is being overdiagnosed, and she will receive unnecessary treatment.

Making a Decision About Mammography

  • Experts recommend that women aged 50 to 74 years undergo a screening mammogram every 2 years.
  • Whether you are likely to benefit from starting mammograms earlier or having them more frequently depends on your risks for breast cancer and your values and preferences. Each woman may feel differently about the possibility of having a false-positive result or being  diagnosed with and treated for cancer that might not have caused problems. It is important for you to consider what these experiences might mean for you. It is also important to consider how you might feel if you decide not to undergo screening mammography and you are later diagnosed with breast cancer, even if the likelihood that mammography would have made a difference is small.

There is an online tool from the National Cancer Institute which you may use to determine with some precision what your personal risk of developing breast cancer is. It’s called the Breast Cancer Risk Assessment Tool.
I found a useful decision aid available through the University of Sydney in Australia.  It takes about 30 minutes to go through the steps.  At the end it gives you the option of documenting your own personal decision aid.

Here is a link to another program for calculating  risk of developing breast cancer. This one is available through the Harvard School of Public Health.  You can click through the series of web pages to input your individual data, and it will give you an estimate for your breast cancer risk.  It is particularly nice in that it can show how you might decrease your risk based on what are called “modifiable factors”, such as weight reduction, nutrition, cessation of smoking or alcohol intake.
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