What does the test involve?
Mammography involves placing the breasts between two glass plates. The breasts need to be compressed to reduce the thickness of the tissue through which the x-rays travel. The breast compression can be uncomfortable or painful.
What does the test cost?
Screening mammography is offered free of charge to most NZ women between the ages of 45 and 69 through a national publicly funded service BreastScreen Aotearoa. The National Breast Screening Unit states that there is “very little benefit” for screening mammography for women aged 70 years and over. BreastScreen Aotearoa does not offer free mammograms to women younger than 45 because of their denser breast tissue means that the test results are harder to read and more women in this age group may experience false positive results.
Other women who want to have mammograms can obtain a referral from a doctor and pay for the service which costs around $160.
What are the potential benefits of the test?
According to the NZ National Screening Unit, “Studies clearly show that when women aged 50 years and over are invited to have mammograms every two years as part of a screening programme, their risk of death from breast cancer is reduced by about a third. For women aged 45 to 49 years, the risk of death from breast cancer is reduced by about a fifth.”
However, not all studies in the medicial literature show an unequivocal benefit to mammography.
An article in the Journal of the National Cancer Institute in 2000 concluded:
“In women aged 50–59 years, the addition of annual mammography screening to physical examination has no impact on breast cancer mortality.”
A Canadian study in which 50,430 women participated found that mammography was no better than a “single breast physical examination and instruction on breast self examination”. The objectives of the study were:
“To compare breast cancer mortality in 40- to 49-year-old women who received either 1) screening with annual mammography, breast physical examination, and instruction on breast self-examination on 4 or 5 occasions or 2) community care after a single breast physical examination and instruction on breast self-examination.”
The authors concluded:
“After 11 to 16 years of follow-up, four or five annual screenings with mammography, breast physical examination, and breast self-examination had not reduced breast cancer mortality compared with usual community care after a single breast physical examination and instruction on breast self-examination.”
What are the risks associated with mammography?
There are a number of risks associated with mammography.
1) First of all there are the risks that apply to breast screening in general (Please refer to the entry “General Risks of Breastscreening”.)
2) Ionising radiation
Mammography also involves exposure to potentially carcinogenic ionising radiation. BreastScreen Aotearoa states that the radiation risk from mammograms is “extremely small”.
The website of Women’s Health Action acknowledges the cancer risk from ionising radiation:
According to the site:
“The radiation risk from modern mammography is extremely low. For a woman attending breast screening every two years from the age of 50 to 64, the possible risk of dying from a breast cancer caused by radiation is estimated to be one in 20,000. For a woman who starts annual mammography at the age of 40, then has it every two years from 50 to 64, there would be one radiation induced breast cancer death per 10,000 women.”
However, according to Dr Samuel Epstein, mammography (as practised in the USA) entails substantial cancer risks:
“Radiation from routine mammography poses significant cumulative risks of initiating and promoting breast cancer (1- 3). Contrary to conventional assurances that radiation exposure from mammography is trivial – and similar to that from a chest X-ray or spending one week in Denver, about 1/ 1,000 of a rad (radiation-absorbed dose)- the routine practice of taking four films for each breast results in some 1,000-fold greater exposure, 1 rad, focused on each breast rather than the entire chest (2). Thus, premenopausal women undergoing annual screening over a ten-year period are exposed to a total of about 10 rads for each breast. As emphasized some three decades ago, the premenopausal breast is highly sensitive to radiation, each rad of exposure increasing breast cancer risk by 1 percent, resulting in a cumulative 10 percent increased risk over ten years of premenopausal screening, usually from ages 40 to 50 (4); risks are even greater for “baseline” screening at younger ages, for which there is no evidence of any future relevance. Furthermore, breast cancer risks from mammography are up to fourfold higher for the 1 to 2 percent of women who are silent carriers of the A-T (ataxia-telangiectasia) gene and thus highly sensitive to the carcinogenic effects of radiation (5); by some estimates this accounts for up to 20 percent of all breast cancers annually in the United States (6).”
Dr Epstein is the author of The Politics of Cancer and has spent the last few decades fighting to reduce the exposure of the American public to carcinogens that are fueling that country’s cancer epidemic.
UPDATE: According to information that I have obtained by making a request under the Official Information Act, for New Zealand women who have mammograms as part of BreastScreen Aotearoa “The average glandular dose [of radiation] must be less that 3mGy (0.3 rad) for a single view of a breast.” (In the BreastScreen Aotearoa, two views are usually taken of each breast, compared to four views of each breast in the example of the American women cited by Dr Epstein. ) This means that the “average” New Zealand’s woman’s radiation exposure from mammography appears to be lower than that of American women – because BreastScreen Aotearoa offers mammograms on a two yearly (rather than an annual) basis and only two images of each breast are taken at most screening sessions.
3) False positive results
Other potential risks from mammography include false positive results which can cause significant anxiety. Biopsy can of suspicious areas of the breast is the only definitive way of determining whether or not a lesion identified on a mammogram does in fact represent cancer or a benign condition.
4) Possible rupture of breast implants
Women who have had breast reconstruction following breast cancer surgery (or for any other reason) should be aware that there is a small risk of the breast implants being ruptured during mammography due to the breast compression involved in this procedure.
“Mammograms require breast compression, which could contribute to implant rupture. According to the FDA adverse event database, there were 41 reported cases of breast implant rupture during mammograms, reported between 1992 and 2002. An additional 17 cases of breast implant rupture during mammograms were reported in the medical literature.
“In addition to special care taken by the radiological technologist to reduce the risk of breast implant rupture during this compression, other techniques are used to maximize what is seen of the breast tissue during mammograms. These techniques are called breast implant displacement views, Eklund displacement views, or Eklund views, named for the radiologist who developed the techniques. These special implant displacement views are done in addition to those views done during routine mammograms.
“Because of the extra views and time needed women with implants should always inform the receptionist or scheduler that they have breast implants when making an appointment for a mammogram. They should also tell the radiological technologist about the presence of implants before a mammogram is performed. Then, the radiological technologist will use these special displacement techniques and take extra care when compressing the breasts to avoid rupturing the breast implant.
“The displacement procedure involves pushing the implant back and pulling the breast tissue into view. Several factors which may affect the success of this special technique, in imaging the breast tissue in women with breast implants, include the location of the implant, the hardness of the capsular contracture and the amount of the breast tissue compared to the implant size.
“Also, when reading the mammogram, the radiologist may find it difficult to distinguish calcium deposits in the scar tissue around the implant from a breast tumor. Occasionally, it is necessary to remove and examine a small amount of tissue (biopsy) to see whether or not it is cancerous. Frequently, this can be done without removing the implant.”
How accurate is the test?
The accuracy of mammography depends partly on the age of the woman being screened.
According to Women’s Health Action website, up to 25% of cancers may be missed in younger women. For older women the test is more accurate. To quote from the site:
“False negative results …This means actual cancers are missed. About 10% of invasive breast cancers are not detected by mammography in women 50-59 years. In women 40-49 up to 25% are missed. False negatives can give women false reassurance that cancer is not present and may delay them reporting symptoms to their doctor.”
Also from this site:
“False positive results … This means a woman is told something is not quite right about her mammogram. She then needs further investigations, usually more mammograms and ultrasound examination. In some cases, a sample of breast cells or tissue is taken. Only a small number of these women will actually have cancer. Up to one in ten women who have mammograms will be brought back for another mammogram or more tests.”
For women with breast implants, the interpretation of mammograms is more difficult as calcified scar tissue around the implant has a similar appearance to a breast tumour.
Further sources of information about mammography:
This medical journal article discusses both mammography and thermography
This site provides information about mammography as well as well as information about breast health and other women’s health issues.
This link at the website of Women’s Health Action provides an overview of the risks and benefits of mammography.
This is the link to the site of the National Screening Unit, which runs BreastScreen Aotearoa