Radiation Risk of Medical Imaging During Pregnancy
What is radiation? Background radiation is always present in our environment. It is inescapable and provides each of us with…Read more
Eight randomized controlled trials dating from the 1970s have shown that mammographic screening for breast cancer reduces the mortality from breast cancer by over 20%.1 Participation in BreastScreen Australia has been shown by case–controlled studies to be associated with a reduction in mortality from breast cancer of over 30%.2,3 An independent breast cancer screening review from the United Kingdom, published in 2012, has estimated that there is a 20% relative risk reduction in breast cancer mortality attributable to mammographic screening in the UK, with an absolute mortality benefit of one breast cancer death prevented for 250 women invited to mammographic screening.4
Screening mammography is a screening test for the early detection of breast cancer. It is directed at women who have no breast symptoms, such as a breast lump, pain, nipple discharge or skin changes. Biennial screening mammography is recommended for women in the 50–69 years age group, but is available to all women aged over 40 years.
The target age group for screening is 50–69 years, the age range for which it has been shown by multiple randomised controlled studies that screening mammography results in a reduction in breast cancer mortality. These women are actively recruited to have screening mammography with BreastScreen Australia.
In New Zealand, free breast screening for women aged 45–69 years is provided by the national breast-screening program, BreastScreen Aotearoa.
Women with a past history of breast cancer are eligible to be screened by BreastScreen. Women who are still under the care of their breast surgeons or oncologists, and women treated with breast conservation surgery, might be more appropriately screened outside BreastScreen in a diagnostic setting. See Diagnostic Mammography.
There are no absolute contraindications to screening mammography.
The relative contraindications for screening mammography are:
Women with symptoms or signs of breast cancer. Such women should undergo diagnostic imaging, which might include additional mammographic work-up (such as magnification mammography), breast ultrasound and needle biopsy. Inappropriate referral of symptomatic women to BreastScreen might result in the delayed or missed diagnosis of breast cancer.
Age less than 40 years in women of usual risk. Screening mammography is less effective in women less than 40 years because of the lower prevalence of breast cancer in this age group and the relatively reduced sensitivity of mammography in younger women who generally have breasts of greater mammographic density.
Pregnancy. Radiation should be avoided, if possible, during pregnancy. In addition, the breast tissue is usually denser during pregnancy, again reducing the sensitivity of mammography.
Women with breast implants. Screening mammography can be carried out in women with breast implants. The risk of damage to the implants is extremely small. However, the presence of implants makes mammography less sensitive and clinical breast examination is more important in these women than for women without implants.
Radiation risk: The risk that the radiation from a mammogram might cause breast cancer is extremely low, especially with the use of low-dose mammography. Such risk is far outweighed by the benefit of early detection of breast cancer (see Radiation Risk of Medical Imaging in Adults and Children). The Health Protection Agency of the United Kingdom estimates the risk of an additional cancer in a lifetime from a single mammographic examination to be in the low risk range: 1 in 100,000 to 1 in 10,000.5 This is the same risk as from the exposure to natural background radiation accumulated over several months to 1 year.
Pain: The breast must be compressed during mammography. The compression is usually uncomfortable. One study6 found that approximately 70% of women described the compression as being mildly to severely painful, and that 2.7% of women indicated that the pain might deter them from having subsequent mammograms. Despite the pain, the compression required for mammography does not harm the breast.
False positive screening mammograms: False positive screening mammograms result in the recall of women without breast cancer for further assessment. There can be morbidity associated with the additional assessment, such as needle biopsies and open biopsies. Anxiety related to screening and assessment can outweigh the benefit of possible early detection of breast cancer.
Approximately 5% of women screened are recalled to assessment, and approximately 10% of these women are diagnosed with breast cancer. This means that nine out of every 10 women recalled after a mammogram turn out not to have breast cancer.
False negative mammograms: Screening mammography does not detect all breast cancers. An interval cancer is a cancer that is diagnosed after a screening examination and before the next screening mammogram is due. This could be because the carcinoma has developed within this interval or because a carcinoma was present but mammographically occult, was present but only as a minimal abnormality, visible only in retrospect, or was present but the mammogram was falsely interpreted as being negative. According to the National Accreditation standards of BreastScreen Australia,7 there should be less than 7.5 cancers per 10,000 women aged 50–69 years screened, presenting within 12 months of a negative screening mammogram. BreastScreen Australia achieves this standard.8
Overdiagnosis: Overdiagnosis of cancer is the diagnosis of a cancer that would never result in symptoms during a person’s lifetime or cause death. However, it is not possible to determine which cancers diagnosed by screening mammography are life threatening and which are not, so some women might receive treatment for a cancer that did not need treatment.4,9,10 The level of overdiagnosis is difficult to estimate because of the absence of reliable data,4 but it has been estimated by an independent breast screening review from the United Kingdom, published in 2012,4 that 19% of cancers diagnosed in women invited to screening are overdiagnosed cancers. The same study estimated that for 10,000 women invited to be screened from the age of 50 years to 70 years, 681 cancers will be diagnosed, of which 129 (19%) will be overdiagnosed and 43 deaths from breast cancer will be prevented.4 The estimates of the balance between benefit and harm vary, and another estimate is that for every case of overdiagnosis, 2 to 2½ lives are saved by mammographic screening.11
No post-procedural care is required. Redness and occasional bruising from the compression can occur, but does not require treatment.
There are two other imaging methods that have a role in screening for breast cancer.
Breast ultrasound: Breast ultrasound has a proven complimentary role when used as a targeted examination after detection of an abnormal clinical and/or abnormal mammographic finding. It might have a role for screening in women with dense breasts (these are most often, but not always, younger women or those taking hormone replacement or the oral contraceptive pill).
There might be an increase of up to 55% in the detection rate of breast cancer when screening ultrasound is added to screening mammography in women with dense breasts. This increase in detection rate comes at a cost of an increased number of needle biopsies carried out, and results in a positive predictive value (PPV) of approximately 9% for cancer following a recommendation for needle biopsy when screening ultrasound is combined with screening mammography. This is lower than the PPV of 23% when screening mammography is carried out without screening ultrasound.12 Population-based screening for breast cancer by ultrasound cannot be recommended, but there might be a role for selected screening of women with dense breasts in combination with screening mammography.
Breast magnetic resonance imaging (MRI): Breast MRI has a role in screening women with a high risk of breast cancer, especially women who are carriers of a genetic mutation for breast cancer, mainly BRCA1 and BRCA2. These women might have in the order of an 85% lifetime risk of developing breast cancer. Other women with a greater than 20% lifetime risk of breast cancer, such as those with a past history of radiation therapy for thoracic Hodgkin disease or a strong family history of ovarian cancer, might benefit from screening with breast MRI. However, MRI screening should only be carried out in a multidisciplinary team framework, and only by radiologists with expertise in both breast imaging and breast MRI. Breast MRI is not recommended for women with a normal risk for breast cancer due to the relatively low specificity of MRI scanning for breast cancer and the relatively low prevalence of breast cancer compared to the high-risk population.
No other imaging modalities are recommended for screening. Thermography and electrical impedance have no role in the investigation of breast cancer and should be avoided.
Frequency of screening mammograms in women with a family history of breast cancer
A woman’s risk profile for breast cancer can be classified as:13
Category 1: At or slightly above normal risk of between 1 in 11 to 1 in 8 lifetime risk of developing breast cancer. This includes women with only 1 first-degree relative diagnosed at over 50 years-of-age.
Category 2: Moderately increased risk of between 1 in 8 and 1 in 4 lifetime risk. This includes women with one first-degree relative with breast cancer diagnosed under the age of 50 years or two first-degree relatives of any age.
Category 3: Potentially high risk of between 1 in 4 and 1 in 2 lifetime risk.
The category into which an individual woman falls can be calculated using the risk calculator (FRA-BOC) provided by Cancer Australia.12
Recommendations for screening mammography are:13
Category 1: 2-yearly mammograms from the age of 40 years.
Category 2: 2-yearly mammograms, with a decision regarding annual mammograms and age of commencement of mammograms determined on an individual basis. As a guide, annual screening mammography can be considered if a woman has a first degree relative with breast cancer diagnosed before the age of 50 years.
Category 3: Screening is optimally carried out after referral to a family cancer clinic. As a minimum, annual mammographic screening is recommended, commencing at an age 5 years less than the youngest relative with breast cancer. Women less than 50 years-of-age might be eligible for a breast MRI. See website of RACGP (the red book) also.
http://www.cancerscreening.gov.au/internet/screening/publishing.nsf/Content/faqs#policy [accessed May 2013]
http://canceraustralia.gov.au/clinical-best-practice/breast-cancer [accessed May 2013]
NSW Breast Cancer Institute
http://www.bci.org.au/[accessed May 2013]
BreastScreen Aotearoa – National Screening Unit, New Zealand
http://www.nsu.govt.nz/[accessed May 2013]
RACGP (the red book) – pages 67–69
1. Tabar l, Duffy S and Smith R. Breast cancer screening: The evolving evidence. Oncology 2012; 26(5): 471–486.
2. Roder D, Houssami N, Farshid G et al. Population screening and intensity of screening are associated with reduced breast cancer mortality: evidence of efficacy of mammography screening in Australia. Breast Cancer Res Treat. 2008; 108: 409–16.
3. Nickson C, Mason KE, English DR and Kavanagh AM. Mammographic screening and breast cancer mortality: A case–control study and meta-analysis. Cancer Epidemiology Biomarkers Prev 2012; 21: 1479–88.
4. Cameron DA, Dewar JA, Thompson SG, Wilcox M, The benefits and harms of breast cancer screening: an independent review, Lancet 2012; 380: 1778-86
5. The Health Protection Agency of the United Kingdom
Information Booklet produced by NRPB, Chilton, Didcot, Oxon OX110RQ
http://www.hpa.org.uk/web/HPAwebFile/HPAweb_C/1194947388410 [accessed May 2013]
6. Keemer-Gels ME, Groenendijk RPR, van den Heuvel JHM et al. Pain experienced by women attending breast cancer screening. Breast Cancer Res Treat 2000; 60(3): 235–240.
7. Breast Screen National Accreditation Standards:
http://www.cancerscreening.gov.au/internet/screening/publishing.nsf/Content/br-accreditation [accessed May 2013]
8. BreastScreen Australia Monitoring Report 2008-2009. Available on-line at http://www.aihw.gov.au/WorkArea/DownloadAsset.aspx?id=10737420596 [accessed May 2013]
9. Puliti D, Duffy S, Miccinesi G et al. Overdiagnosis in mammographic screening for breast cancer in Europe: a literature review. J Med Screen 2012; 19 Suppl 1: 42–56.
10. Cancer Australia, Position statement over diagnosis from mammography screening. Available on-line at http://canceraustralia.gov.au/about-us/position-statements/over-diagnosis-mammography-screening [accessed January 2013]
11. Duffy S, Tabar L, Olsen A, Vitak B et al. Absolute numbers of lives saved and overdiagnosis in breast cancer screening, from a randomized trial and from the Breast Cancer Screening Programme in England. J Med Screen 2010; 17: 25–30.
12. Berg W, Blume J, Cormack J et al. Combined Screening With Ultrasound and Mammography vs. Mammography alone in Women at Elevated Risk of Breast Cancer, JAMA 2008: 209(18); 2151–2163.
13. Cancer Australia Familial Risk Assessment FRA-BOC. Available on-line at http://canceraustralia.gov.au/clinical-best-practice/gynaecological-cancers/familial-risk-assessment-fra-boc [accessed May 2013]
Page last modified on 15/6/2018.
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