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Breast Cancer Risk Assessment
Early detection and treatment of breast cancer reduces breast cancer–related mortality. Evaluating and predicting an individual woman’s risk of developing breast cancer are important for tailoring screening regimens and breast cancer prevention strategies in order to facilitate early detection. Knowledge of risk determination will help a radiologist communicate knowledgeably with patients and referring providers about breast cancer risk and screening strategies.
Definitions: Average Versus Higher-Than-Average Risk
Knowledge of a woman’s risk is important in creating screening and prevention recommendations appropriate to the level of risk. In the United States, one in eight women will develop breast cancer during her lifetime, so an average-risk woman has an estimated lifetime risk of developing breast cancer of approximately 13% (1/8). A woman is considered high risk if she has a 20% or greater lifetime risk of developing breast cancer. Women with an estimated lifetime risk of developing breast cancer from 15% to less than 20% are at higher-than-average risk of developing breast cancer but do not meet the designated threshold of a 20% lifetime risk. Unlike the high-risk subgroup (that has well-defined screening guidelines), supplemental screening recommendations for this intermediate-risk subgroup lack consensus ( Box 10.1 ).
Box 10.1
Breast Cancer Risk: Definitions
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Average risk: ~13% estimated lifetime risk of developing breast cancer
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Higher-than-average risk:
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High risk: 20% or greater estimated lifetime risk of developing breast cancer
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Intermediate risk: 15% to <20% estimated lifetime risk of developing breast cancer
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The American College of Radiology (ACR) and Society of Breast Imaging (SBI) recommend that all women undergo a breast cancer risk assessment by age 30 to identify high-risk women who would benefit from supplemental screening. A formal risk assessment, utilizing a risk assessment model, can be used to estimate an individual’s lifetime risk of developing breast cancer (see section titled: Models for Risk Assessment”).
Population Subgroups at Higher Risk
Certain population subgroups are widely recognized as carrying a 20% or greater lifetime risk of developing breast cancer without the use of a formal risk assessment model ( Box 10.2 ).
Box 10.2
Population Subgroups With High Risk of Developing Breast Cancer
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Disease-causing genetic mutations (such as BRCA1, BRCA2, TP53, PTEN, STK11, PALB2, ATM, CHEK2, CDH1, NBN ) and hereditary syndromes associated with an increased risk of developing breast cancer
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First-degree relative with BRCA mutation (or any other autosomal dominant deleterious genetic mutation known to increase breast cancer risk) but the patient herself remains untested
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History of chest radiation therapy before age 30
Genetic Mutation Carriers and Hereditary Syndromes
About 5% to 10% of women diagnosed with breast cancer have an associated genetic mutation. The BRCA1 and BRCA2 mutations are the most widely recognized; however, the use of multigene panel testing in recent years has identified additional pathogenic variants associated with an increased risk of developing breast cancer.
The lifetime risk of developing breast cancer is 50% to 85% among BRCA1 mutation carriers and approximately 45% among BRCA2 mutation carriers. Because the BRCA1 and BRCA2 mutations are seen at a higher frequency in individuals with Ashkenazi Jewish ancestry, incorporation of ethnicity and race is important in a detailed risk assessment. Other, less common pathogenic variants include TP53 (Li-Fraumeni syndrome; 85% lifetime risk), PTEN (Cowden and Bannayan-Riley-Ruvalcaba syndrome; 25%–85% lifetime risk), STK11 (Peutz-Jeghers syndrome; 45%–50% lifetime risk), PALB2 (interacts with BRCA2 ; 35% lifetime risk), CDH1 (hereditary diffuse gastric cancer; 39%–52% lifetime risk), ATM (ataxia-telangiectasia; 33%–38% lifetime risk), CHEK2 (28%–37% lifetime risk), and NBN (30% lifetime risk). The National Comprehensive Cancer Network (NCCN) routinely updates its published guidelines on which genetic mutation carriers require early and more rigorous breast cancer screening.
Chest/Mantle Radiation Before Age 30
Women who have been treated with chest or mantle radiation therapy before age 30 with a collective dose of ≥10 Gy are at a high risk for developing breast cancer. To put it in perspective, a Hodgkin lymphoma survivor receiving mantle radiation therapy at age 25 will have an estimated 20% to 25% risk of developing breast cancer by age 45, similar to a BRCA mutation carrier. Patients treated with chest radiation in the first and second decades of life and those receiving ≥20 Gy are at greatest risk for developing a breast malignancy. As such, the American Cancer Society (ACS) and ACR recommend that women who have a history of chest radiation therapy before age 30 begin annual screening mammography at age 25 or 8 years after radiation therapy (whichever is later). In addition, the ACS and ACR recommend annual supplemental screening with breast magnetic resonance imaging (MRI) beginning at age 25 to 30.
Family History of Breast Cancer
Important factors to consider during evaluation of a patient’s family history include the number of family members with breast cancer, the number of maternal and paternal first- and second-degree relatives with breast cancer, and the age of the family members at diagnosis. The ACS therefore recommends the use of risk assessment models that incorporate significant family history in order to identify women with a high estimated lifetime risk of developing breast cancer who should undergo supplemental screening with breast MRI. It is important to remember that the vast majority of women who develop breast cancer have no family history of breast cancer.
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