Breast Cancer Prevention

Medical Author: Edward White, MD
Revising Author: Melissa Conrad Stöppler, MD
Revising Medical Editors: William C. Shiel Jr., MD, FACP, FACR and Dennis Lee, MD

• Introduction to breast cancer prevention
• What are the biological causes of breast cancer?
• What are the risk factors for developing breast cancer?
• What is the importance of early breast cancer detection?
• What are the advantages and limitations of mammography?
• How frequently should women undergo mammography and breast examinations?
• What is the risk of radiation with repeated mammography screening over the years?
• Are there any controversies in the area of breast cancer screening?
• How helpful are BRCA1 and BRCA2 genetic tests in identifying women at risk?
• What is the link between estrogen and breast cancer?
• What are breast cancer prevention treatments?
• Are there other breast cancer prevention measures?
• Conclusion

Families with Breast Cancer Medical Author: Carolyn Janet Crandall, MD, FACP Medical Editor: William C. Shiel Jr., MD, FACP, FACR Ms. G. is a 40-year-old woman with two small children. Like most women, she is concerned about her chances of developing breast cancer. She asks her doctor about her risks. Although breast cancer is a worry for most women, Ms. G. is especially worried because of a family history of breast cancer. Her mother and sister had breast cancers that were diagnosed at young ages. A woman with a family history of breast cancer has a lot of concerns. Among other things, she is thinking of her job, children, and husband, as well as how her medical insurance and health team will be able to serve her needs in the future should a crisis arise. What are the facts about families that have multiple members with breast cancer? Inherited breast cancer disorders account for a small minority of breast cancers overall. Genes are the "messages" in each cell of the body that determine the ultimate design of our bodies. Genes can be damaged by the environment. Additionally, people can be born with defects in the genes that remove the body's defenses against cancers. Only in about 10% of all breast cancer cases is there actually a genetic defect that can be tested. This means that 90% of breast cancers are due to other causes. In fact, most cases of breast cancer occur in women who do not have a family history of breast cancer. A complex interplay between environmental and genetic factors affect the development of breast cancer, and all the key factors have not yet been identified. Learn what increases a woman's risk of developing breast cancer » Top Searched Breast Cancer Terms: type, research, male breast cancer, statistics, awareness, prevention, warning signs, treatment, mammogram, mastectomy, breast biopsy, inflammatory breast cancer

Introduction to breast cancer prevention

For so many women, there is no more dreaded disease than breast cancer. Breast cancer elicits fears related to loss of body image and sexuality, surgery, and death. As is the case for most cancers, the exact cause of breast cancer is not clearly known. Furthermore, there is currently no cure for advanced disease, and there is no definitive way of preventing it.

Our knowledge of how breast cancer develops is expanding rapidly. As a result, new medications are being developed to reduce the risk of breast cancer among women at high risk of contracting this disease. For the majority of women, lifestyle changes, a healthy diet, cautious use of selected antioxidants, exercise, and weight reduction can also help reduce the chance of developing breast cancer. To date, the most important strategy in improving survival is still breast cancer screening and early detection. Breast cancer is the second leading cause of cancer deaths among women in the United States. The leading cause is lung cancer. One in every eight women in the United States develops breast cancer. The risk is even higher for women with previous breast cancer, those who have first-degree relatives with breast cancer, those with multiple family members with cancer, and those who have inherited "cancer genes."

What are the biological causes of breast cancer?

Breast cancer, like all cancers, initially develops because of defects in the genetic material deoxyribonucleic acid (DNA) of a single cell. The human body is composed of trillions of cells. Inside the inner core (nucleus) of each cell is our DNA located on chromosomes. Every human cell has two sets of 23 chromosomes. Each set is inherited from one parent. DNA exists as long, spiraled strands on these chromosomes. Different segments along the DNA strands contain information for various genes. Genes are blueprints that provide genetic instructions for the growth, development, and behavior of every cell. Human DNA is thought to contain approximately 50,000 to 100,000 genes. Most genes carry instructions for the types and the amount of proteins, enzymes, and other substances produced by the cells. Genes also govern the sizes and the shapes of the organs by controlling the rate of division of the cells within these organs. (During cell division, a cell makes a duplicate copy of its chromosomes and then divides into two cells.) Some genes restrict cell division and limit tissue growth.

Defects on the DNA strands can lead to gene coding errors, which in turn can cause diseases. When genes that normally restrict cell growth and divisions are absent or defective, the affected cells can divide and multiply without restraint. The cells that divide and multiply without restraint enlarge (forming a tumor) and can also invade adjacent tissues and organs. These cells can further break away and migrate to distant parts of the body in a process called metastasis. The ability to multiply without restraint, the tendency to invade other organs, and the ability to metastasize to other parts of the body are the key characteristics of cancers—characteristics that are due to DNA defects.

The cancer-causing DNA defects can be acquired at birth (inherited) or may develop during adult life. The inherited DNA defects are present in every cell of the body. On the other hand, DNA defects that develop during adult life are confined to the descendants (products of cell divisions) of the single affected cell. Generally, inherited DNA defects have a greater tendency to cause cancers and cancers that occur earlier in life than DNA defects that develop during adult life.

Research has shown that 5%-10% of breast cancers are associated with mutations (defects) in two genes known as breast cancer-associated (BRCA) genes, BRCA1 and BRCA2. These genes function to prevent abnormal cell growth that could lead to cancer. Every cell in the body has two BRCA1 or BRCA2 genes, one inherited from each parent. A woman who has received one defective BRCA1 or BRCA2 gene from one parent and a healthy gene from the other is called a carrier of the defective BRCA gene. Even though only one healthy BRCA1 or BRCA2 gene is needed to help prevent cancerous growth of cells, the one remaining healthy BRCA gene is vulnerable to damage during adult life by environmental factors such as toxins, radiation, and other chemicals such as free radicals. Therefore, women bearing a defective BRCA1 or BRCA2 gene are at an increased risk of developing breast and ovarian cancers. Women carrying defective BRCA1 or BRCA2 genes also tend to develop these cancers earlier in life.

Other rare genetic mutations are also associated with an increased risk for the development of breast cancer, including mutations of the tumor suppressor gene p53, the CHEK-2 gene, and the ATM (ataxia-telangiectasia mutation) gene.

Since inherited DNA defects account for only 5%-10% of breast cancers, the majority of breast cancers are due to DNA damages that develop during adult life. Environmental factors that can cause DNA damage include free radicals, chemicals, radiation, and certain toxins. But even among individuals without inherited cancer-causing DNA defects, their vulnerability to DNA damage, their ability to repair DNA damage, and their ability to destroy cells with DNA damage, are likely to be genetically inherited. This is probably why the risk of cancer is higher among first-degree relatives of breast cancer patients even among families that do not carry the defective BRCA1 and BRCA2 tumor-suppressing genes.

Some of the errors in the normal control mechanisms allow the accumulation of additional errors in other parts of the system. These errors may lead to gene silencing of critical control genes or the overactivity of other growth-stimulating genes by activation of promoter sites adjacent to these otherwise normal genes.

Other substances such as estrogen (a female hormone) and certain fatty acids may also increase the risk of breast cancer by stimulating the growth and division of cells of the breast tissue.

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