Does Mammography Reduce Mortality?

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Screen shot 2012 09 29 at 11.31.45 PM Does Mammography Reduce Mortality?

A new report on the benefits and risks associated with mammography and breast examinations to screen for breast cancer in asymptomatic women has proven to be quite controversial.

The U. S. Preventative Task Force (USPTF) was put together by a group of experts from around the country. Their conclusions that current research data is insufficient to warrant teaching women to do breast self exams and also against the use of routine mammography to screen for breast cancer in women younger than 50 or older than 74 has been met with widespread criticism. In addition they recommended reducing screening mammography in women 50-74 to every other year rather than annually.1 The USPTF's recommendations conflict with long standing medical advice for all American women to do breast self exams and have annual mammograms starting at age 40.

It seems likely that part of the criticism of this new USPTF report is that the benefits of screening mammography and breast self exams (BSE) have been greatly exaggerated while their potential harm has been largely ignored by physicians and so not surprisingly their patients as well.

In fact as this USPTF reports, two large BSE studies outside the US have failed to find any reduction in the risk of dying from breast cancer. Obviously BSE does no direct harm but it does lead to more testing and treatments, which can lead to both physical and psychological harm. Given those facts it is easy to see why the USPTF recommended against continuing this practice. The same is true for clinical breast exams (CBE) by physicians so again the USPTF recommends against continuing to do CBE. The primary harm in the case of both BSE and CBE is they both lead to additional tests and procedures that fail to significantly reduce the risk of dying from breast cancer. Why would this be so? Probably because most breast cancers are slow growing and do not spread easily from the primary site sort of like basal cell or squamous cell skin cancers. However, about 15 to 20% of breast cancers are aggressive sort of like melanomas. These far more aggressive cancers are much more frequent in women with the BRCA 1 and 2 mutations. They grow more quickly and unfortunately have almost always spread (called metastasis) from their primary site before they are large enough to be detected by BSE or CBE. This is probably why neither of these screening exams have been shown to reduce deaths from breast cancer.

Mammograms can often detect tumors too small or diffuse to be felt by physical examination of the breast so the hope was that this screening test might catch these aggressive tumors much sooner before they have spread. Unfortunately, at least 80 to 90% of these aggressive breast cancers have already metastasized when detected by mammography. Once this happens curing these breast cancers is unlikely although drugs that block estrogen can certainly slow tumors that are estrogen sensitive.

Indeed, the USPTF report estimated that routine mammography may reduce breast cancer mortality by about 15% but even this estimate is likely excessively optimistic. Why? A comprehensive review of studies on the use of mammography to reduce breast cancer mortality found a significant bias in favor of mammography versus control because it was more likely a death from breast cancer was misclassified as another type of cancer in the mammography group than the control. This may be why there is no compelling data demonstrating a reduced risk of total mortality or even cancer mortality in women screened for breast cancer with mammography.2 However, the USPTF made the recommendation to discontinue routine mammography even assuming the optimistic estimate that perhaps 15% of breast cancer deaths could be prevented if women in their 40s underwent annual mammograms, because the harm caused by over diagnosis appeared greater than the very modest potential reduction in mortality from breast cancer.

Another reason to question the use of routine mammography is a recent study which suggested it leads to the diagnosis and treatment of breast cancers that would have disappeared on their own. In this study researchers examined the natural history of breast cancer in Norwegian women 50-64 who either had a mammogram every 2 years for 6 years or a similar group of women were not offered routine mammography. Not surprisingly, 57% more women in the mammography group were diagnosed and treated for invasive breast cancer than in those not screened. When the women not screened during the study period were given a mammogram some were found to have undiagnosed invasive breast cancer. However, even with these additional cases of breast cancer added to the control group’s total they still had 22% fewer cases of invasive breast cancer than those screened every two years. This raises the possibility that many breast cancers diagnosed with routine mammography would have regressed by themselves with no treatment.3 The known and suspected harm caused by the treatment of invasive breast cancers with surgery, radiation, and chemotherapy is substantial and it is doubtful that the at best modest reduction in breast cancer mortality from screening mammography would be sufficient to outweigh the proven and likely risks.

There are certainly many ways to reduce the risk of breast cancer that are more effective than screening mammograms. More importantly these strategies reduce the risk of developing breast cancer (something mammography never does) and also reduce the overall risk of dying - again something mammography has never been shown to do.

These risk reducing ways include:

  • Eat a diet low in fatty meats and refined sugars and higher in vegetables, fruits and whole grains. A recent study of Chinese women found that those adopting a more Western-style diet with more meats and sweets had over twice the risk of dying from breast cancer as those that stuck with a more traditional Chinese diet of soy and vegetables.
  • Reconsider your hormone replacement therapy decision. There is now no doubt that hormone replacement therapy increases the risk of dying from breast cancer by about 24%, which is far more than mammography might reduce it in postmenopausal women.
  • Getting adequate sunshine vitamin D, exercising and maintaining a healthy body weight especially before puberty and after menopause all reduce the risk of developing breast cancer.
  • Exercise and lower body fat stores delays puberty while a rich Western diet and inactivity brings on early puberty, which greatly increases breast cancer risk.
  • In older women increased body fat stores raise estrogen levels and delay menopause both of which greatly increase the risk of breast cancer.
  • It has also been shown that consuming alcohol even in moderation (1-2 drinks/day) likely increases the risk of breast cancer substantially more than even the most optimistic studies on mammography might reduce the risk of breast cancer mortality.
  • And finally growing data suggest having babies earlier in life and breast-feeding them reduces the risk of developing and dying from breast cancer.

By James J. Kenney, PhD, RD, LD, FACN.

1. Ann Intern Med 2009;151:716-26

2. Lancet 2001;358:1340

3. Arch Intern Med 2008;168:2311

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