Screening With Mammography
The latest assessment from the National Cancer Institute on screening mammography can be found at: http://www.cancer.gov/cancertopics/pdq/screening/breast/healthprofessional/page1#Section_13
Screening information usually begins with ‘benefits’, as does the information on the above site, but I am setting out the harms first since (to me) these far outweigh the benefits.
Harms Based on solid evidence, screening mammography may lead to the following harms:
- Overdiagnosis and Resulting Treatment of Insignificant Cancers: Diagnosis of cancers that would otherwise never have caused symptoms or death in a woman’s lifetime can expose a woman to the immediate risks of therapy (surgical deformity or toxicities from radiation therapy, hormone therapy or chemotherapy), late sequelae (lymphedema), and late effects of therapeutic radiation (new cancers, scarring, or cardiac toxicity). (My comment – risks of effects of treatment are lifelong and effects may be lifelong, debilitating, disabling and negatively impact on quality of life – see Lymphoedema Support Network).
Magnitude of Effect: Varies with patient age, tumor type, and grade, and is greater with the first screen than subsequent screening examinations.[3,4] Of all breast cancers detected by screening mammograms, up to 54% are estimated to be results of overdiagnosis.
- False-Positives with Additional Testing and Anxiety.
Magnitude of Effect: On average, 10% of women will be recalled from each screening examination for further testing, and only 5 of the 100 women recalled will have cancer. Approximately 50% of women screened annually for 10 years in the United States will experience a false-positive, of whom 7% to 17% will have biopsies.[7,8] Additional testing is less likely when prior mammograms are available for comparison.
- False-Negatives with False Sense of Security and Potential Delay in Cancer Diagnosis.
Magnitude of Effect: 6% to 46% of women with invasive cancer will have negative mammograms, especially if they are young, have dense breasts,[9,10] or have mucinous, lobular, or rapidly growing cancers.
- Radiation-Induced Breast Cancer: Radiation-induced mutations can cause breast cancer, especially if exposure occurs before age 30 years and to high levels such as from mantle radiation therapy for Hodgkin disease. One Sv is equivalent to 200 mammograms. Latency is at least 8 years, and the increased risk is lifelong.[12,13]
Magnitude of Effect: Between 9.9 and 32 breast cancer cases per 10,000 women exposed to a cumulative dose of 1 Sv, the risk being higher in younger women. Cumulative average environmental radiation can be estimated to be about 1 Sv in 30 years. This 1 Sv is acquired in 30 years cumulative average environmental radiation or in about 200 mammograms. By contrast, one computed tomography scan is associated with exposure to 4 Sv of radiation.[12,13]
Benefits (My comment – It is important to note THE ABSOLUTE MORTALITY BENEFIT.)
Based on solid evidence, screening mammography may lead to the following benefit:
- Decrease in breast cancer mortality
Magnitude of Effect: In the randomized controlled trials (RCTs), for women aged 40 to 74 years, screening with mammography has been associated with a 15% to 20% relative reduction in mortality due to breast cancer. Absolute mortality benefit for women screened annually for 10 years is approximately 1% overall, ranging from 4 per 10,000 for women who start screening at age 40 years to 50 per 10,000 women who start at age 50 years.
More detailed information with study design, validity, reference links etc at: http://www.cancer.gov/cancertopics/pdq/screening/breast/healthprofessional/page1#Section_13
In the UK, the NHS screening programme continues – with its age extension programme surreptitiously recruiting women to a randomised controlled trial – despite the harms.
Still think mammography screening will save your life?