October is Breast Cancer Awareness Month. This is a good time to learn more about breast cancer and how it affects the body, risk factors, prevention, and treatment. Breast cancer occurs when cells in the breast begin to grow out of control. Breast cancer can start in one breast or both. While breast cancer occurs mostly in women, it can affect men as well.

About Breast Cancer

Breast cancer is the most common cancer for women in the United States, apart from skin cancer. Breast cancer accounts for about 1 in 3 new cancers diagnosed in women each year. The lifetime risk of a woman developing breast cancer is about 13 percent, or 1 in 8. Breast cancer is the second leading cause of cancer death for women. More than 43,000 women will die from breast cancer in the United States in 2023. 

There are different types of breast cancer, and the type depends on the part of the breast where the cancer begins. Lobules are glands in the breast that make milk. Lobular cancer begins in lobules. Ducts are small canals that come out of lobules and carry milk to the nipple. Ductal cancers begin in the ducts. Less common breast cancers can begin the nipple, fat and connective tissue, and blood or lymph vessels in the breast. Breast cancers can spread if cells reach the blood or lymph systems where they can then spread to other parts of the body. There are several different treatment options for breast cancer. 

The most common treatment is surgery. Other types of treatment include radiation, chemotherapy, targeted drug therapy, immunotherapy, and hormone therapy. While it isn’t known exactly what causes breast cancer, there are certain risk factors. Some risk factors include age, alcohol use, physical activity, race/ethnicity, birth control use, not having children, and not breastfeeding. 

Genetics & Mutations

Family history of breast cancer and specific genes or gene changes, or mutations, are other common risk factors for breast cancer. Gene mutations can be passed down, or they can occur on their own. Genetic mutations that are passed down, or inherited, are often called family cancer syndromes. One family cancer syndrome linked to breast cancer and other cancer is Hereditary breast and ovarian cancer syndrome (HBOC). HBOC is a genetic condition that makes someone more likely to get breast, ovarian, prostate, pancreatic, and other cancers. 

HBOC can occur in people with a family history without mutations, or it can be specifically linked to genes and mutations. It is often linked to the specific genes BRCA1 and BRCA2. BRCA genes are tumor suppressor genes. These genes control how often cells divide. For those with BRCA gene mutations, this suppressing ability can be changed or turned off. The gene no longer controls cell growth and division, and cancer is more likely to develop as a result. Overall, about 3 percent of breast cancers are related to inherited BRCA1 and BRCA2 mutations. These breast cancer cases often develop at younger ages than other breast cancers. 

BRCA & Genetic Mutation Research

A link between family history and breast cancer was explored as early as the 1940s. Researchers wondered whether this connection was due to genetics (nature) or similar lifestyles and exposures (nurture). After multiple decades, genetics seemed the most likely. However, scientists didn’t discover exactly which genes influenced breast cancer risk until the 1990s when BRCA1 was discovered by pioneer geneticist Dr. Mary-Claire King. In the 1980s, King and her colleagues interviewed 1,579 breast cancer patients under age 55 to learn more about their family histories of breast and ovarian cancer. The researchers used mathematical modeling to analyze family patterns of breast and ovarian cancer. They estimated that genetics must account for about 4% of families in the study. For these families, lifetime breast cancer risk was 82%, compared to 8% for the general population.

Now that a genetic link was made, researchers needed to find the responsible gene. Dr. King and colleagues began another study, this time with 23 extended families. The families included a total of 329 relatives, with a total of 146 invasive breast cancer cases. The study participants provided blood samples that the researchers analyzed and genotyped. Based on this analysis, researchers found a likely region for the gene on chromosome 17 in 1990. Four years later, the exact gene (BRCA1) was located and sequenced, with BRCA 2 found soon after.

Over the last three decades, scientists have discovered thousands of mutations in BRCA1 and 2 genes. These genes can also have relationships with other genes that impact cancer risk. People with BRCA1 mutations have a 60% risk of developing breast cancer before age 70 and a 40% risk of developing ovarian cancer. People with BRCA2 mutations have a 45% risk of developing breast cancer before age 70 and a 25% risk of developing ovarian cancer.

Genetic Testing, Screening, & Treatment

Due to the dramatically increased risk of cancers for those with BRCA mutations, it is important for people with family history of breast cancer to know their risk and act accordingly. One method to find this out is through genetic counseling. Genetic counselors can estimate a person’s likelihood of having a BRCA mutation based on their family history of cancer, personal history, and other factors. If that likelihood is high, an individual can choose to be tested for BRCA mutations. 

If a person does have BRCA mutations, they can choose from a variety of options with their doctor’s guidance. One important path is to undergo earlier and/or more frequent breast cancer screening. This can catch breast cancer earlier, especially since BRCA mutations often lead to breast cancer development at earlier ages. Your doctor will also discuss cancer prevention measures and lifestyle changes, such as maintaining a healthy weight, exercising, diet, and more. Some individuals may choose to take preventive oral medication, such as tamoxifen or raloxifene, or to undergo preventive surgery like a mastectomy. However, these measures come with risks and side effects, so it is important to discuss these options with your doctor and determine the best path forward for you as an individual. 

When people with BRCA mutations do develop breast cancer, it is important for oncologists to know your family history and your mutation status. This is because cancer treatments can be tailored to target specific genetic mutations. For example, a drug called PARP inhibitors are effective at reducing breast cancer progression for those with BRCA mutations. This is because the specific drug blocks DNA repair processes in cancer cells, slowing or even stopping tumor growth. Researchers continue to study BRCA mutations and other family cancer syndromes to determine the best paths forward to prevent cancer, lower risk, and ensure the best treatment outcomes for all patients.