Using Genetic Information and Other Risk Factors to Understand Breast Cancer Risk

Oncology Briefs: Research from the ASCO Educational Book
October 4, 2016
Allison W. Kurian, MD, MSc

The ASCO Educational Book is a collection of articles written by ASCO Annual Meeting speakers and oncology experts. Published annually, each volume highlights the most compelling research and developments across the multidisciplinary fields of oncology such as surgery, radiation, symptom management, health services research, international perspectives, and immunology, among other topics.

In collaboration with Cancer.Net, authors of the ASCO Educational Book have tailored their articles for patients and their loved ones so that they may be similarly informed of the latest science in oncology to improve their care and outcomes.

Dr. Kurian is an Associate Professor at Stanford University, with specialties in breast cancer, cancer prevention, and genetics. She is also the Director of the Stanford Women’s Clinical Cancer Genetics Program and a Cancer.Net Specialty Editor.

Many factors can cause breast cancer to develop. By considering all known factors, researchers are creating powerful tools to predict a woman’s risk for breast cancer more accurately. share on twitter These tools combine a patient’s genetic, lifestyle, and hormonal risk factors to find the risk level. These risk levels can be used by doctors and their patients to make health decisions for individual women and to help reduce the risk of breast cancer in all women.

How a woman’s risk of breast cancer is determined

Several tools to figure out the risk of breast cancer are available for women who have not already been diagnosed with breast cancer. These tools, called risk prediction models, take into account different risk factors to estimate the chances that a woman will develop cancer. These risk prediction models fall into 1 of 2 broad categories:

  1. Empirical models, which consider family history, but do not consider a patient’s genetic information

  2. Genetic models, which consider both known and unknown genetic effects in cancer development

For breast cancer and many other diseases, genetic models have the advantage. However, to calculate a person’s risk of developing breast cancer, doctors must consider her family history, genes, and other hormonal and lifestyle risk factors.

Doctors often use “multiplex sequence panel” testing to analyze a patient’s DNA for inherited changes, or mutations. This testing method can use 1 test to analyze more than 100 genes that are associated with cancer. These panels can find some genetic mutations that have a high risk of causing breast cancer to develop.

Breast cancer is about twice as common among first-degree relatives of people already diagnosed with breast cancer, such as parents, siblings, and children. This is known as “familial relative risk.” The most commonly detected gene mutations associated with a high risk of breast cancer are BRCA1 and BRCA2. Mutations in these genes increase the risk of developing breast cancer by 5 to 10 times. Rare mutations in other genes associated with breast cancer account for about 5% to 10% of breast cancer diagnoses. More than 100 genetic “typos” (known as single nucleotide polymorphisms) found in human DNA are thought to be responsible for another 16% of breast cancer diagnoses. This means that all of the known genetic risk factors explain around 38% to 41% of breast cancer diagnoses. This also means that 50% of the risk factors for breast cancer are unknown.

Using risk assessment tools to screen for and prevent breast cancer

Risk prediction tools help doctors and patients choose screening and prevention strategies. Screening and prevention approaches for breast cancer include:

  • Mammograms

  • Breast MRI

  • Lifestyle changes

  • Preventive surgery and drug treatment

Screening for breast cancer

Most breast cancer screening guidelines recommend that women start routine mammograms at age 40 to 45 years and possibly having them every other year instead of annually. These new recommendations apply to women who have an average risk of developing breast cancer. Women who are at high risk, such as women with a relative who has been diagnosed with breast cancer, need a more intensive approach.

Breast MRIs have been recommended to screen women who have a higher risk of developing breast cancer. Breast MRIs are more sensitive than mammograms for detecting cancers in women with a BRCA1 or BRCA2 mutation and in women who have a family history of breast cancer. There are some concerns about this screening technique, including its high cost. However, many guidelines now recommend an annual breast MRI for women who have an increased risk of breast cancer because it is capable of finding breast cancer early.

Preventing breast cancer

Many studies have shown that obesity, lack of exercise, tobacco use, and alcohol use can increase risk for developing breast cancer. Women should talk with their doctors about what they can do to reduce their risk through diet, exercise, and lifestyle changes.

Preventive surgery is another prevention option for some women with an increased risk for breast cancer. For example, some women who discover they have high-risk gene mutations choose to undergo bilateral risk-reducing mastectomies (removal of both entire breasts) to prevent breast cancer from developing. Risk-reducing mastectomy is a complicated preventive decision that should be made only after careful conversations have happened between the patient and her medical team.

As we learn more about the genetic components of breast cancer risk, it becomes more important for patients and health care providers to communicate effectively with each other. Those conversations are becoming more challenging as well. It is critical that patients and health care providers discuss all risk factors and the risk and benefits of the available screening and prevention options.

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