1.1 Introduction to Breast Cancer Screening
1.2 What Are The Models for Predicting Breast Cancer Risk?
1.3 Breast Cancer Screening Rates and Mortality Reduction
1.4 What Are The Latest Recommendations for Breast Cancer Screening?
1.5 What is the Reduction in Breast Cancer Mortality Due to Screening?
1.6 What are the Benefits and Risks of Breast Cancer Screening?
1.6.3 Recommendations for 6-Monthly Mammograms
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Breast cancer screening programs have created a large amount of clinical and research data. This published data can be found in the literature and accessed on the internet.
Introduction to Breast Cancer Screening
Breast cancer mammographic ‘screening‘ is done to detect abnormalities in the breast that may require monitoring or treatment. The most important role of mammography is to detect early, treatable breast cancer.
For every 1,000 women who are screened, between 3 and 5 breast cancers will be detected. There is evidence that breast cancer screening programs are saving lives, by detecting breast cancer at an early and more treatable stage.
Another important goal of breast cancer screening programs is to encourage women to begin to participate in screening at an earlier age and to have re-tests every one to two years.
The most common forms of breast cancer develop in the breast ducts and lobules. Because a malignant tumor of the breast develops from the lining epithelial cells of these structures, it is called a ‘carcinoma,’ more commonly termed ‘cancer’ or ‘malignant tumor.’
An ‘invasive’ breast cancer has spread from the breast ducts or lobules and into the surrounding normal breast tissue.
The World Health Organization (WHO) have calculated the new cases of breast cancer in the U.S. and the mortality from breast cancer in the U.S. in 2014:
- New cases: 232,670 (female); 2,360 (male)
- Deaths: 40,000 (female); 430 (male)
When a breast lump is discovered by breast self-examination, it is likely to be benign in 80% of cases. There is no evidence that the introduction of breast self-examination has reduced mortality rates from breast cancer.
What Are The Models for Predicting Breast Cancer Risk?
There are models to calculate an individual’s lifetime risk of developing breast cancer and there are models that predict an individual’s likelihood of having a BRCA1 or BRCA2 gene mutation.
But each of these models is only appropriate when the patient’s detailed clinical characteristics are examined, together with their family history.
The two common risk assessment models (Gail, 1989; Claus et al., 1993) were developed within particular populations, and may not be applicable worldwide. The Claus model and the Gail model are often used in clinical patient counseling and in research studies. But both methods have their limitations, with the risk estimates derived from the two models sometimes giving different risk predictions for each patient analyzed (Gail, 2010).
Several models have been developed to predict the probability of identifying germ line BRCA1/BRCA2 mutations, either in individual patients or in families.
These models have included using logistic regression, Bayesian analysis of genetic models and also empiric observations, including the use of prevalence tables, such as Myriad.
Using complex segregation analysis, a polygenetic model (BOADICEA) examines both breast cancer risk and the probability of having a BRCA1 or BRCA2 mutation (Antoniou et al., 2004). Access to this is now available to individuals on line (BRCAPRO and Breast and Ovarian Analysis of Disease Incidence and Carrier Estimation Algorithm [BOADICEA])
Breast Cancer Screening Rates and Mortality Reduction
The longer the time interval between screenings, the greater the likelihood of detecting breast cancer.
For yearly screening, the cancer detection rate is between 0.5% and 0.6%. For 2-year screening, the detection rate increases to between 0.65% to 0.85%, while the three-year screening interval detects cancers at a rate of 1.0% to 1.3%.
Women aged between 50 and 69 years of age should be screened for breast cancer approximately every 18 months, regardless of risk factors.
The American Cancer Society and the National Cancer Institute (NCI) both recommend annual or bi-annual screening for women between 40 and 49 years of age, if at average risk.
However, recent evidence suggests that tumors may grow more rapidly in younger women, so the trend is to recommend annual screening for all women aged between 40 and 49 years of age.
For women between 40 and 49 years of age, and for women over 70 years of age, breast screening should be done annually if there are risk factors present that make breast cancer more likely.
Risk Factors for Breast Cancer include:
- A family history of breast cancer (sister, mother, daughter).
- Previous chest or thoracic radiation therapy history (e.g., for Hodgkin’s lymphoma) before the age of 30 years.
- Family history of BRCA1 and BRCA2 gene variants.
- First pregnancy at 30 years of age or older.
- Late menopause.
- More than four years of hormone replacement therapy (HRT).
Early detection with the most appropriate treatment is the most effective strategy to reduce breast cancer mortality.
Mammography screening for breast cancer is not only expensive but involves substantial manpower and financial resources. It is not a feasible approach in developing countries.
Studies on the efficacy of early detection programs, based on clinical breast examination (CBE) and breast self-examination (BSE) remain inconclusive and rather controversial.
There are three main approaches that could improve patient survival in breast cancer:
- Firstly, increasing the awareness of the population of important breast cancer symptoms and signs.
- Second, more information on the improved prognosis associated with treatment of early-stage disease needs to be understood by patients.
- Third, the provision of readily accessible and effective diagnostic and treatment services are important.
What Are The Latest Recommendations for Breast Cancer Screening?
Since 2009, the American Academy of Family Practitioners (AAFP) recommends that family physicians should discuss with each patient under the age of 50, the benefits of screening for breast cancer. The AAFP recommends biennial (every two years) screening mammography for women between ages 50 and 74. The AAFP concludes that the current evidence is insufficient to assess the benefits and harms of screening mammography in women aged 75 years and older.
The United States Preventive Services Task Force (USPSTF) has summarized the current best evidence regarding breast screening to help to guide physicians and patients. The recommendations of the USPSTF are intended to apply to women who are not at increased risk of developing breast cancer and apply to routine screening procedures.
The latest recommendations for breast cancer screening, for early breast cancer detection in women without breast symptoms, come from the American Cancer Society (ACS) in September, 2014.
This is a summary of the recommendations, taken from the full ACS report:
- Women age 40 and older should have a mammogram every year and should continue to do so for as long as they are in good health.
- Women in their 20s and 30s should have a clinical breast exam (CBE) as part of a periodic (regular) health exam by a health professional preferably every 3 years.
- Starting at age 40, women should have a CBE by a health professional every year.
- Breast self-exam (BSE) is an option for women starting in their 20s. Women should be told about the benefits and limitations of BSE. Women should report any breast changes to their health professional right away.
- Women who are at high risk for breast cancer based on certain factors should get an MRI and a mammogram every year. This includes women who:
- Have a lifetime risk of breast cancer of about 20% to 25% or greater, according to risk assessment tools that are based mainly on family history (such as the Claus model).
- Have a known BRCA1 or BRCA2 gene mutation.
- Have a first-degree relative (parent, brother, sister, or child) with a BRCA1 or BRCA2 gene mutation, and have not had genetic testing themselves.
- Had radiation therapy to the chest when they were between the ages of 10 and 30 years.
- Have Li-Fraumeni syndrome, Cowden syndrome, or Bannayan-Riley-Ruvalcaba syndrome, or have first-degree relatives with one of these syndromes.
- The American Cancer Society recommends against MRI screening for women whose lifetime risk of breast cancer is less than 15 %.
The American Cancer Society (ACS) concludes:
“Without question, a physical exam of the breast without a mammogram would miss the opportunity to detect many breast cancers that are too small for a woman or her doctor to feel but can be seen on mammograms.
Mammograms are a sensitive screening method, but a small percentage of breast cancers do not show up on mammograms but can be felt by a woman or her doctors. For women at high risk of breast cancer, such as those with BRCA gene mutations or a strong family history, both MRI and mammogram exams of the breast are recommended.”
The full recommendations from the American Cancer Society, September 2014, can be found here.
What is the Reduction in Breast Cancer Mortality Due to Screening?
Mortality reduction as a result of breast cancer screening has been reported to be as high as 40% over ten years. Statistics shows a recall rate of about 6%.
It has been estimated that for every woman’s life saved by breast cancer screening, the number of women who have to be screened is between 470 to 500.
For women aged between 40 and 49 years of age, there is a reduction in the mortality rate from breast cancer, when screening is done at intervals of less than two years. The growth rate for breast cancer is typically more rapid for women in the 40 to 49 year age group.
Screening for breast cancer is recommended every 12 to 18 months. It is estimated that the mortality rates from breast cancer may be reduced by almost 30% by screening at this interval.
Mortality rates from breast cancer in women aged between 50 and 69 years may be reduced by almost 40% by regular screening.
The National Cancer Institute (NCI) has reported that when screening mammography commenced at age 40 to 49 years, it resulted in a 5% decrease in mortality rate during a 5 year period, and a 25% decrease in mortality rate during an 18 year period.
If screening is initiated in the 50 to 64 year old age group, there is a 40% decrease in mortality at 9 years, a 30% decrease in mortality at 10-14 years, and a 21% decreased mortality rate at 18 years.
But, a major concern is compliance with breast cancer screening programs. Women over 50 years of age seem to be far more inclined to attend annual screening checkups when compared to women under 50 years of age
Breast cancer survival rates vary greatly worldwide. They range from 80% or more in Sweden, Japan and North America to around 60% in developed countries and below 40% in developing countries (Coleman et al., 2008).
Low survival rates for breast cancer in women in undeveloped countries is explained mainly by the lack of early detection programs. This lack of early detection of breast cancer results in a high proportion of women presenting with late-stage disease. In less developed countries, the problem is compounded by a shortage of adequate diagnosis and treatment facilities.
What are the Benefits and Risks of Screening Mammography?
As mammographic screening results in the reduction of mortality due to breast cancer, the expected benefits are believed to outweigh the risks. It must also be remembered that this is a non-invasive way to examine the breast tissue.
Breast cancer detection with mammography uses a low-dose X-ray as the initial diagnostic tool. As with all X-rays, there are potential risks to the procedure. Frequent use of X-rays of any kind is not recommended for young people.
The average glandular dose of radiation for two exposures with a grid is about 1.6 to 2.0 mGy (0.16-0.2 rad). The average dose of radiation from a breast X-ray is about the same as background radiation exposure during a round trip by airplane from Denver to New York or travelling 1000 km in a car. The benefits of breast cancer screening vastly outweigh the potential health risks due to radiation exposure.
i. ‘False Negative’ Mammography
Mammography can image up to 90% of the breast tissue, which means there is a 10% chance that if a small tumor is present, it may not be detected; this is called a ‘false negative‘.
ii. ‘False Positive’ Mammography
A ‘false positive’ refers to a finding of a tissue abnormality which is non-cancerous.
iii. Early Recall for Follow-Up Imaging
Requests for follow-up imaging create a high degree of anxiety. About 9 % of women who are re-called for follow-up because they have a screening abnormality, will not attend.
Women who perceive a higher than average level of cancer in their extended family tend to be the most motivated to attend a follow-up mammogram.
Of course, the majority of follow-up mammograms turn out to show benign breast changes.
Recommendations for 6-Monthly Mammograms
Diagnostic mammography at six-monthly intervals is recommended as follow-up for any recent breast preservation surgery for cancer. Scans should be made every six months for the first five years for the affected breast and every year for the non-affected breast.
Other breast problems, such as spontaneous nipple discharge, a personal or family history of breast cancer, or other histological anomalies from a previous biopsy, are indications for a follow-up mammography.
Gail, M.H., Brinton, L.A., Byar, D.P., et al. (1989). Projecting individualized probabilities of developing breast cancer for white females who are being examined annually. J Natl Cancer Inst 81, 1879-86. doi: 10.1093/jnci/81.24.1879 (Retrieved October 23rd 2014): http://www.ncbi.nlm.nih.gov/pubmed/2593165?dopt=Abstract
Gail, M.H., Mai, P.L. (2010). Comparing breast cancer risk assessment models. J Natl Cancer Inst 102(10), 665-8. (Retrieved October 24th 2014): http://jnci.oxfordjournals.org/content/102/10/665.long
American Cancer Society American Cancer Society recommendations for early breast cancer detection in women without breast symptoms. (Retrieved February 12th 2015): http://www.cancer.org/cancer/breastcancer/moreinformation/breastcancerearlydetection/breast-cancer-early-detection-acs-recs
Centers for Disease Control and Prevention (CDC) What are the Risk Factors for Breast Cancer. (Retrieved February 12th 2015): http://www.cdc.gov/cancer/breast/basic_info/risk_factors.htm
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