Concerns Surrounding Mammography: Radiation exposure, Accuracy, and Usefulness in Decreasing Cancer Mortality

By Robert A. Erickson, M.D., F.A.A.F.P.

SHOULD SCREENING PROCEDURES BE COMPLETELY SAFE?

I would like to point out that there is a difference between screening procedures and diagnostic procedures. Screening procedures, which we all assume should be 100% safe, are used to look periodically at symptom-free people for some undetected disease. For example, a Pap smear in women screens for cervical cancer or pre-cancerous changes, or a PSA test in men screens for possible prostate cancer. Screening detects rather than prevents disease, and it makes sense the earlier a problem is uncovered, the better the odds of fixing it. By contrast, diagnostic procedures are evaluations of people who already have some suspicious symptoms that may indicate a potential problem. So the question arises, is it safe to expose a healthy woman’s breasts to radiation year after year as a screening procedure?

The answer, in my opinion, is NO. There are no long term studies that I am aware of demonstrating the safety of multiple, repeated mammogram radiation exposures on normal breast tissue. I am not talking about evaluation of a breast lump, where the benefits of the procedure outweigh the risks.

WHAT IS A “SAFE” DOSE OF RADIATION?

A growing number of physicians and researchers are concerned about the cumulative dose of radiation persons living in the US receive over a life time from medical and dental procedures. Think back over your life time and count up all the dental x-rays, chest x-rays, CT scans, radioactive dyes, mammograms, bone density scans or other radiographic procedures that you have had. The risk of cancer development goes up in direct proportion to the total radiation dose received. But who is monitoring the doses you receive? When I was doing my training in Radiation Oncology I was required to always wear a dosimetry badge to monitor radiation exposure.

Sami Sherbini for the Nuclear Regulatory Commission stated there is no safe radiation dose if by safe is meant no risk. What is talked about is “acceptable risk.” But what may be an acceptable risk to one person may not be an acceptable risk to another.

ROUTINE SCREENING MAMMOGRAPHY: A RISK- BENEFIT DILEMMA

The current gold standard for breast cancer screening is mammography and clinical breast exam by a physician. The United States is the only country where mammography has been promoted to pre-menopausal women and aggressively to most women on an annual basis. In November 2009 The United Sates Preventive Taskforce, an independent panel of experts in prevention and primary care appointed by the federal Department of Health and Human Services, changed the recommendations for women receiving screening mammograms. They advised women to start at age 50 (not 40) and to undergo mammography every 2 years (not annually). Dr. Diana Petitti, vice chairwoman of the task force and professor of Biomedical Informatics at Arizona State University, said the guidelines were based on new data and analyses and were aimed at reducing the potential harm for over-screening. She was quoted in an N.Y. Times article, “While many women do not think a screening test can be harmful, medical experts say the risks are real. A test can trigger unnecessary further tests, like biopsies, that can create extreme anxiety. And mammograms can find cancers that grow so slowly that grow so slowly that they never would be noticed in a woman’s lifetime, resulting in unnecessary treatment.”

The European’s take a much more conservative approach with mammograms being performed in post menopausal women every 2-3 years instead. Agencies such as the American Cancer Society and the National Cancer Institute have assured the American population that this procedure is both safe and effective in reducing breast cancer deaths through earlier detection. Contrary to these assurances and popular belief, there is a growing body of evidence that screening for breast cancer with mammography is unjustified. This topic is controversial for a variety of reasons and the reader is reminded that the purpose of this web site is educational and to provide information.

  • A January 2000 article in Lancet, one of the most prestigious and conservative medical journals in the world, analyzed eight breast cancer mammography trials. Because there was conflicting conclusions in the earlier studies regarding the benefit of mammography, the investigators from the different studies were asked for further details. Baseline imbalances were shown for 6 of the 8 trials, and inconsistencies in the number of women randomized were found in 4. The 2 adequately randomized trials found no effect of screening on breast-cancer mortality. The Lancet study concluded, after the inconsistencies were corrected and the data reanalyzed, that “there is no reliable evidence that [mammography] screening decreases breast-cancer mortality.”
  • It may come as a surprise that over 90 percent of the women who develop breast cancer discover the tumor themselves. A recent study in Canada (Canadian National Breast Cancer Screening Study) involved 40,000 women, aged 50 to 59 on entry. Half the women performed monthly BSE (breast self exam) following the instruction of trained nurses, had annual CBEs (clinical breast exams) by trained nurses, and had annual mammography. The other half practiced monthly BSE and had annual CBE but no mammograms. This study found that the addition of annual mammography screening to the physical exam had no impact on breast cancer mortality. A Japanese mass screening study further demonstrated the effectiveness of CBE. In spite of this evidence, the American Cancer Society and radiologists just dismissed the studies as not being a substitute for mammography.
  • John W. Gofman, M.D., Ph.D. is a Professor Emeritus of Molecular and Cell Biology at the University of California, Berkley, and an expert on biocellular effects of radiation and chromosome damage. In his book Preventing Breast Cancer: The Story Of A Major, Proven, Preventable Cause Of This Disease, Dr. Gofman points out that if a woman, starting at age 50, accumulates 15 mammograms over her lifetime and assuming that the mean glandular dose to the breast per 2 view exam is 0.2 rads, the likelihood of a fatal mammogram-induced breast cancer is roughly 1 in 500. If a woman receives more than 15 mammograms or starts at an earlier age, the risk of developing a breast cancer from this X-ray procedure goes up. The bottom line of his book is the recent increase in breast-cancer incidence is not a mystery. He documents how 75% of the annual incidence is caused by earlier exposure to ionizing radiation from X-rays.
  • G. J. Heyes and A. J. Mill of the Radiation Biophysics Group at the University of Birmingham, UK, compared mammography X-rays and atomic bomb spectrum radiation for neoplastic potential. The full study was published in Radiation Research 162, 120-127 December 2004. Mammography radiation delivers a “low-energy” 29 kVp X-ray that has a much more destructive effect on cells than higher energy types of X-ray. The researchers used a standard mammography unit identical to those used in breast cancer screening and a high energy X-ray source that matched the spectrum of radiation the Nagasaki atomic bomb survivors were exposed to. In this study, even though the per unit dose from both sources was the same, they found the risks associated with mammography screening to be up to 5 times higher than previously assumed and that the low-energy mammography X-rays were more hazardous than previously assumed. The researchers stated that the risk-benefit relationship of mammography exposure needs to be re-examined.

For more on radiation related issues you may wish to log on to
www.x-raysandhealth.org.

Additional points of concern about mammography:

  • Mammography has an overall 25% false positive rate (indicates a cancer is present when it is not), leading to unnecessary biopsies. 85% of mammography initiated biopsies are negative, but cause additional expense and emotional upset in the patient’s involved.
  • Mammography has an overall 20% false negative rate (missed cancerous tumor) in women below the age of 60, and up to 40% false negative rate in women under age 50 due to dense breast tissue.
  • Not all anatomic areas of the breast are visualized with mammography. Large breasts, dense breasts, fibrocystic breasts, and women who have had implants present difficulties in mammography interpretation.
  • Not all breast cancers are slow growing. Especially in pre-menopausal women, cancers tend to be more aggressive, rapidly doubling in size, and are more likely to metastasize. Women can be lulled into a false sense of security by a supposedly negative result on an annual mammogram and fail to seek medical attention.