Information on Screening Mammography– COMPREHENSIVE

Here is the abstract from a recent article published on this issue of deciding whether to perform screening mammography.

A Systematic Assessment of Benefits and Risks to Guide Breast Cancer Screening Decisions

Lydia E. Pace, MD, MPH; Nancy L. Keating, MD, MPH

  JAMA. 2014;311(13):1327-1335. doi:10.1001/jama.2014.1398.

Importance: Breast cancer is the second leading cause of cancer deaths among US women. Mammography screening may be associated with reduced breast cancer mortality but can also cause harm. Guidelines recommend individualizing screening decisions, particularly for younger women.
Objectives: We reviewed the evidence on the mortality benefit and chief harms of mammography screening and what is known about how to individualize mammography screening decisions, including communicating risks and benefits to patients.
Evidence Acquisition:  We searched MEDLINE from 1960-2014 to describe (1) benefits of mammography, (2) harms of mammography, and (3) individualizing screening decisions and promoting informed decision making. We also manually searched reference lists of key articles retrieved, selected reviews, meta-analyses, and practice recommendations. We rated the level of evidence using the American Heart Association guidelines.
Results:  Mammography screening is associated with a 19% overall reduction of breast cancer mortality (approximately 15% for women in their 40s and 32% for women in their 60s). For a 40- or 50-year-old woman undergoing 10 years of annual mammograms, the cumulative risk of a false-positive result is about 61%. About 19% of the cancers diagnosed during that 10-year period would not have become clinically apparent without screening (overdiagnosis), although there is uncertainty about this estimate. The net benefit of screening depends greatly on baseline breast cancer risk, which should be incorporated into screening decisions. Decision aids have the potential to help patients integrate information about risks and benefits with their own values and priorities, although they are not yet widely available for use in clinical practice.
Conclusions and Relevance:  To maximize the benefit of mammography screening, decisions should be individualized based on patients’ risk profiles and preferences. Risk models and decision aids are useful tools, but more research is needed to optimize these and to further quantify overdiagnosis. Research should also explore other breast cancer screening strategies.

Drs. Nancy Keating and Lydia Pace, from Brigham and Women’s Hospital in Boston performed an extensive search of published literature regarding the benefits and risks of screening mammography in older women, and summarized their findings.  They sought to differentiate among the various age categories of women undergoing screening mammography, comparing evidence of decreased breast cancer mortality versus some defined risks.

As you might guess, the results vary depending on which studies are included.  In my reviewing the information provided, it seems likely that there is a 10-20% decrease in breast cancer mortality over a 10 year period, if one includes all women undergoing screening mammography. But two recently reported Canadian trials looking at 25 year results failed to show any benefit in mortality for screening mammography.

The authors also investigated “harms” from screening mammography, emphasizing a high false positive rate, which leads to additional studies, biopsies, anxiety, and “over diagnosis”.  The concept of over diagnosis is somewhat difficult to comprehend or explain.  The concept of over diagnosis is strongly implied from randomized trials in which half the patients do not undergo any screening.  If a study is randomized, it can be safely assumed that there should be a similar number of breast cancers ultimately diagnosed in each group.  But what has occurred in these studies is that there is a higher number of breast cancers diagnosed in the screened group than in the unscreened group.  The only logical conclusion is that there are some cancers identified at screening which would never have become clinically apparent.  However, if a cancer is diagnosed by screening, there is no way to determine if that particular cancer is a clinically irrelevant or one or not, so all diagnosed cancers are similarly treated.

I do feel that the conclusions offered by the investigators are rational.  They note that the benefit for screening is higher if it is applied to a group of women who have a higher risk for developing breast cancer to start with.  Also, if there are multiple comorbidities, which shorten the patient’s life expectancy, the benefit for screening mammography will be proportionately reduced.  Also, the individual’s level of concern and anxiety about a possible cancer diagnosis ought to be factored into the decision-making.

The main problem I see with the conclusion is that there is just not enough time to provide a one-on-one discussion with all women regarding the benefit: risk ratio for them individually, even though it would be nice if we could.  This summary hopefully will provide information in a way that will help you make up your own mind, or allow you to focus on some particular questions for your primary care physician.  It is important to know that there is no right or wrong answer about screening mammography.  But as a general rule, the higher one’s risk, the greater the benefit from screening.  The shorter one’s life expectancy is, the less benefit there is to be gained from screening.

As women age, they obviously are moving closer to end of life.  Screening mammography plays little role in the last 5-10 years of a woman’s life.  Of course, we rarely know when the last 5-10 years of a woman’s life begins.  But to the extent that we can estimate or predict that, we can make some rational decision about when to discontinue screening mammography.  There are Internet tools for predicting one’s life expectancy.  These tools could be utilized to help decide when to discontinue screening mammography.  More generally, one might continue screening mammography until one’s general health begins to fail, or if there is some other major disease threatening your life, or if your ability to easily travel to the mammography facility is impaired.

Here is an example of how one might use personal information to decide when to stop screening mammography.  Mrs. Jones is 83 years old and generally healthy.  She had a sister who died of breast cancer in her 50s.  She herself has never had breast cancer.  She has no breast symptoms. She has hypertension which is well controlled.  She has been getting screening mammograms since she was 45 years old annually.  She uses the Internet site  to calculate her life expectancy, and gives her a mean life expectancy of 11 years, which would be age 94.  She may subjectively conclude that she is probably in the upper quartile of women her age in terms of health, so may reasonably predict that she might live actually to age 96, or 13 years.  With this information, she might choose to continue screening mammography for about 3 more years, then stop.

On the other hand, Mrs. Smith, is 79 years old, has congestive heart failure, diabetes, hypertension, and previous stroke.  She uses a different Internet site (either one could be used, but don’t be surprised that you get different results with each one.  Remember, these are algorithms that are just making an estimate based on certain criteria.).  Her calculated life expectancy is only 5 years, due to her multiple medical problems.  For her, it probably doesn’t make any sense to continue screening mammography, since the benefit for screening is to find cancers which may impact your life expectancy beyond the 5-10 year range.  So even if she has a cancer that might be found only on screening, it probably wouldn’t decrease her lifespan if left undetected.

For younger women, say under age 65-70, life expectancy calculations probably play less role in making the decision about screening, unless one has many major medical problems.  So at these younger ages, it probably makes sense to simply follow the usual recommendations of screening mammography every year.  In some other countries, the recommendation is every 2 years rather than annually though I suspect that women are much less likely to stick with their schedule if a two-year interval is used.  But this would be a reasonable option for some women, if their anxiety about a breast cancer diagnosis is low, and there is no pertinent family history of breast or ovarian cancer.

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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