Mammography: A Question of Safety
By Deborah Pate, DC, DACBR
It is estimated that for one woman to avoid dying from breast cancer, up to 1000 women will have at least one "false alarm," which half of whom will undergo biopsy and breast cancer will be over diagnosed in 5 to 15 women, who will be treated needlessly with surgery, radiation, chemotherapy, or a combination. -- H. Gilbert Welch, MD, MPH, in "Screening Mammography - A Long Run for a Short Slide?" NEJM, Sept. 23, 2010.
Many women would say it's worth it for the one woman and that they are willing to tolerate the risk of undergoing biopsy and/or treatment to save the life of another. But do we have all the facts? Simply put, no. We have been debating the relative merits of screening mammography for over a decade despite the wealth of data that suggests the test is a close call in terms of the benefits (which are modest) and the harm, which is rarely discussed. All women hear is that mammography saves lives, period.
No screening test is 100 percent accurate; that's why it's called a "screening" test. Most people would agreed that if a screening test requires surgery to determine whether a positive test is truly positive, one would first want to know more about the statistical accuracy of the test before even agreeing to it. The other question would be, is this test safe? What is the probability of the test itself causing some harm? The possibility of harm in mammography is rarely discussed. Let's explore some of the known harmful effects of mammography:
Mammography itself is radiation; as with most carcinogens, there is a latency period or delay between the time of irradiation and the potential occurrence of breast cancer. This delay can vary up to decades for different people. Response to radiation is especially dramatic in children; women who, as children, received breast and chest X-rays have shown increased rates of breast cancer as adults.
The usual dose of radiation during a mammographic X-ray is from 0.25 to 1 rad with the very best equipment; that's 1-4 rads per screening mammogram (two views each of two breasts). If a woman has annual mammograms from age 55 to age 75, she will receive a minimum of 20 rads of radiation. For comparison, women who survived the atomic bomb blasts in Hiroshima and Nagasaki absorbed 35 rads. Though one large dose of radiation can be more harmful than many small doses, it is important to remember that damage from radiation is cumulative.
How much radiation have you received over your lifetime? Do you have any idea? Determine your cumulative exposure by visiting the American Nuclear Society Web page and reviewing the radiation dose chart (www.new.ans.org/pi/resources/dosechart/).
Screening mammography may be detrimental for women at high risk for developing breast cancer. According to new research presented last year at the Radiological Society of North America (RSNA) conference, the low doses of radiation associated with annual screening mammography could be placing high-risk women in even more jeopardy of developing breast cancer, particularly if they start screening at a young age or have frequent exposure.
In a meta-analysis of six studies, it was found that women with BRCA1 orBRCA2 gene mutations, or a family history of breast cancer, who were exposed to radiation, either from mammography or chest X-rays, before the age of 20 had a risk for breast cancer that was 2.5 times higher than their counterparts who were not exposed to radiation. In this analysis, in which 8,500 high-risk women were examined, five or more mammograms increased risk twofold.
Marijke C. Jansen-van der Weide, PhD, from the University Medical Center Groningen in the Netherlands, reported these findings, stating that exposure to low-dose radiation increased breast cancer risk by 1.5 times as compared with no exposure. The mean age of the women in the analysis was 45 years. The cumulative dose of radiation they received ranged from 0.3 to 24 mSv.
Errors in Diagnosis
Errors in diagnosis lead to unnecessary treatment. The cumulative risk for false-positive mammography results has been reported as 21 percent to 49 percent after 10 mammography examinations for women in general and up to 56 percent for women ages 40 to 49 years. Diagnosing the earliest stage of breast cancer is difficult, prone to both outright error and case-by-case disagreement over whether a cluster of cells is benign or malignant.
Because of the technological advances in mammography, the increased diagnosis of DCIS (ductal carcinoma in situ) is astounding. In 1983, there were 4,900 U.S. cases of DCIS. By 2008, that number had increased to 67,770 (Nelson Report, 2009). It is estimated that by 2020, more than 1 million U.S. women will be living with DCIS.
According to BreastCancer.org, DCIS is not generally malignant but is routinely treated aggressively. Many experts believe that the overtreatment of DCIS has increased the number of "breast cancer survivors" and improved the cure rate from the disease because we are now "curing" a condition that may have never progressed into a malignancy. Presently, there is no consensus on how DCIS should be treated and specific pathological categories have to be completely worked out.
Women ages 40-49 have higher risk of false-positive screens, according to a 2007 review for the American College of Physicians that focused on screening mammography in women 40-49 years of age. It included publications from the original mammography trials as well as 117 other studies. The reviewers found that the studies have estimated a 7-23 percent relative risk reduction in breast cancer mortality rates with screening mammography in women in this age group. They also found rates of false-positive results as high as 20-56 percent after 10 mammograms, leading to increases in unnecessary procedures and breast cancer-related anxiety.
These reviewers concluded that the evidence suggests that more women in the 40-49 age range have risks that outweigh the benefits of screening mammography. Subsequently, the American College of Physicians issued detailed guidelines for screening mammography among younger women that encourage doctors to carefully assess an individual woman's risks for breast cancer, and to discuss with them the potential benefits and harms of screening mammography in order to make informed individual decisions about screening.
Presently for 50-year-old women, the 10-year risk of developing breast cancer is about four per 1,000 women in the United States. If we assume that mammography screening is associated with a 10 percent reduction in the rate of death from breast cancer, the risk estimate without mammography would be about 4.4 per 1,000 women. In other words, 2,500 women need to be screened over a 10-year period for one to avoid death from breast cancer. What happens to the other 2,499 women who underwent screening to achieve this benefit is also relevant. Estimates of harm vary considerably.
The Power of Information
I am not against mammography. I would not claim to be an expert in mammography, but the data clearly demonstrate that mammography is not always beneficial and that adverse outcomes are higher in some premenopausal women. Even when the federal government amends the guidelines as a result of exhaustive research and new data, controversy remains. I am simply recommending that all women should be made aware of the present guidelines so they can make an informed decision.
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