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Specialist Advice — 8 minutes

Are screening mammograms still a good idea?

Raymond Lepage, PhD, Doctor in Biochemistry
Raymond Lepage, PhD, Doctor in Biochemistry
Science popularizer

Breast cancer is the most common cancer that afflicts women. It is estimated that 12% of Canadian women (1 in 8) will develop breast cancer during their lifetime and 3% will die from it. Due to improvements in diagnostic and therapeutic approaches, the five-year survival rate has significantly increased to over 85% in recent years. Nevertheless, breast cancer remains the second-leading cause of death from cancer in women, and it is estimated that 14 Canadian women die from the disease every day [1].

As with other cancers, the sooner breast cancer is diagnosed, the better the outcome. This is why every Canadian province has developed cancer screening programs for woman aged 40–69. The Quebec Breast Cancer Screening Program (QBCSP), a voluntary program based on screening mammograms every two years, was launched in 1998. It is offered at no-charge to all women, but the actual participation rate is around 60%, 10 points under the MSSS objective of 70% participation. Many issues have been raised, however, concerning the safety, comfort, and efficacy of screening mammograms. Looking at the studies, most of these questions are pretty straightforward to answer.

Real also: How to prepare for a mammogram

Do mammograms save lives?

In early programs, a 20% reduction of mortality due to breast cancer was observed. So yes, mammograms were clearly shown to save lives. However, with the development of new therapeutic approaches in the last 40 years, it has become much more difficult to identify which specific aspect of treatment contributed most to the overall increase (from 75% to 90%) in the five-year breast cancer survival rate: screening, improved diagnostic tools or better therapeutic approaches.

Is breast palpation still a valid form of screening?

Even in the hands of well-trained physicians or nurses, screening through clinical breast examination is controversial and its use is declining. Well-designed clinical trials were unable to confirm that breast examination reduces breast cancer mortality. Many guidelines including the Canadian Task Force on Preventive Health Care have removed clinical breast examination from their recommendations. But this position is not unanimous. According to many organizational guidelines, the presence of a palpable mass in combination with a normal mammogram should be submitted at least to ultrasonography [8].

Do screening programs miss some breast cancers?

A false negative mammogram is defined as a normal looking mammogram where breast cancer is actually present. It is estimated that screening mammograms do not find about 20% of breast cancers [7]. A false negative result at a screening test means that the required treatment will be delayed. Repeating the mammogram every two years will definitively reduce the number of false negative results.

Is the radiation from a mammogram dangerous?

Mammograms do expose the breast to radiation. In a typical mammogram (2 views of each breast) with modern equipment, the total exposure is very small and corresponds to the amount that everyone gets from their natural surroundings over about 7 weeks (FN10). X-ray exposure from a mammogram corresponds to 40% of the exposure during a spine X-ray. Most health authorities think that the risk of X-ray exposure from a mammogram every two years is negligible compared to the risk of developing an aggressive breast cancer.

Read also: To which extent X-rays are a health hazard?

Do screening programs lead to overdiagnosis?

To reduce the burden on the overall system, and stress on patients, every screening program is set up to identify the maximum number of individuals that may have the disease. Only those individuals that were positive at the screening test will be submitted to more invasive and expensive testing. False positive results are therefore implicitly part of all screening programs.

In the case of breast cancer, confirmatory testing includes, in order, a confirmatory mammogram, breast echography using ultrasounds, in some cases MRI, and a breast biopsy. It is estimated that 9% of all screening mammograms return false positives where no cancer is ultimately present. Only 7% of all positive screening tests ultimately indicate breast cancer [2].

False positive results are more common among younger women, those that have dense breasts, have had prior breast biopsies, breast cancer in the family, or are taking estrogen [3]. The availability of a previous mammogram has a greater effect on reducing the number of false positives. Improvements in radiological equipment (digital mammograms, etc.) [4] and use of AI (artificial intelligence) [5] are other promising avenues.

Over diagnosis is different from a false positive that will be eliminated by confirmation testing. Over diagnosis applies to cases where a breast cancer is definitely present but is not life-threatening (small, slow growth, no metastasis), and would have never needed treatment if it had not been detected in the first place by a screening mammogram.

Over diagnosed women may in turn be over treated, as they become exposed to numerous unnecessary adverse effects that are associated with cancer treatment. The number of such cases is very difficult to evaluate but it is estimated that 10 to 30% of all breast cancers cases are over treated [6]. This being said, it is actually impossible for the clinician (and the patient) to determine if the cancer present is indolent or will evolve!

Peut-on rendre les mammographies moins douloureuses ?

Compared to ultrasonography or MRI, mammography is a painful exam. Although of short duration (10-15sec), breast compression is severe enough that it is reported as the reason for half of the women not attending a repeat screening mammogram. Although there are ways to alleviate the pain, there may be good news in the future for women with more sensitive breasts. New mammography equipment recently introduced in Ontario and Alberta allows women to self-adjust the pressure on their own breasts. This approach has been tested before in Europe and the USA, and it was observed that the mammogram results were as good as those obtained with traditional mammographic equipment. In many cases, women actually self-applied more pressure than that typically applied by the technician [9].

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  1. “Breast Cancer Statistics.” Canadian Cancer Society. Accessed October 1, 2019. https://www.cancer.ca/en/cancer-information/cancer-type/breast/statistics/?region=on.
  2. Organized Breast Cancer Screening Programs in Canada: Report on Program Performance in 2007 and 2008. Toronto, ON: Canadian Partnership Against Cancer, 2013. http://publications.gc.ca/collections/collection_2015/aspc-phac/HP32-1-2008-eng.pdf
  3. “Limitations of Mammograms: How Often Are Mammograms Wrong?” American Cancer Society. Accessed October 1, 2019. https://www.cancer.org/cancer/breast-cancer/screening-tests-and-early-detection/mammograms/limitations-of-mammograms.html.
  4. Pisano, Etta D., Constantine Gatsonis, Edward Hendrick, Martin Yaffe, Janet K. Baum, Suddhasatta Acharyya, Emily F. Conant, et al. “Diagnostic Performance of Digital versus Film Mammography for Breast-Cancer Screening.” New England Journal of Medicine 353, no. 17 (2005): 1773–83. https://doi.org/10.1056/nejmoa052911.
  5. Vyborny, C J, and M L Giger. “Computer Vision and Artificial Intelligence in Mammography.” American Journal of Roentgenology 162, no. 3 (1994): 699–708. https://doi.org/10.2214/ajr.162.3.8109525.
  6. Elmore, Joann G., and Suzanne W. Fletcher. “Overdiagnosis in Breast Cancer Screening: Time to Tackle an Underappreciated Harm.” Annals of Internal Medicine 156, no. 7 (March 2012): 536. https://doi.org/10.7326/0003-4819-156-7-201204030-00012.
  7. “Mammograms.” National Cancer Institute. Accessed October 1, 2019. https://www.cancer.gov/types/breast/mammograms-fact-sheet.
  8. Provencher, L., J.c. Hogue, C. Desbiens, B. Poirier, E. Poirier, D. Boudreau, M. Joyal, C. Diorio, N. Duchesne, and J. Chiquette. “Is Clinical Breast Examination Important for Breast Cancer Detection?” Current Oncology 23, no. 4 (August 2016): 332. https://doi.org/10.3747/co.23.2881.
  9. Henrot, Philippe, Martine Boisserie-Lacroix, Véronique Boute, Philippe Troufléau, Bruno Boyer, Grégory Lesanne, Véronique Gillon, et al. “Self-Compression Technique vs Standard Compression in Mammography.” JAMA Internal Medicine 179, no. 3 (January 2019): 407. https://doi.org/10.1001/jamainternmed.2018.7169.
  10. “Mammogram Basics: How Does A Mammogram Work?” American Cancer Society. Accessed October 1, 2019. https://www.cancer.org/cancer/breast-cancer/screening-tests-and-early-detection/mammograms/mammogram-basics.html.