Breast Cancer Prevention

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.
Breast cancer also affects men. Male breast cancer accounts for about 1% of all breast cancers. Over 200,000 new cases of breast cancer are diagnosed each year in women in the U.S., while about 2,000 cases are diagnosed in men.
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 those 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 cells, like all cancers, initially develop 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.

What are the risk factors for developing breast cancer?

The most significant risk factors for breast cancer are gender and age. Men can develop breast cancer, but women are 100 times more likely to develop breast cancer than men. Breast cancer is 400 times more common in women who are 50 years old as compared to those who are 20 years old.
Family history
Another important risk factor is having first-degree relatives (mother, sister, or daughter) with breast cancer or male relatives with prostate cancer. The risk is especially higher if both the mother and sister have had breast cancers, if the cancers in first-degree relatives occurred early in life (before age 50), or if the cancers in these relatives were found in both breasts. Having a male relative with breast cancer and having both relatives with breast and ovarian cancers also increase a woman's risk of developing breast cancer. Families with multiple members with other cancers may have a genetic defect leading to a higher risk of breast cancer.
Women who have inherited defective BRCA1, BRCA2, p53, and DNA repair genes have an increased risk of developing breast cancer, sometimes at early ages, as discussed previously. But even in the absence of one of the known predisposing genetic defects, a strong family history may signify an increased risk because of genetic or environmental factors that are specific to that particular family. For example, increased risk in families could be due to exposure to similar environmental toxins in some cases.
Previous breast cancer
A woman with a history of breast cancer can develop a recurrence of the same breast cancer years later if the cancer cells had already spread to the lymph nodes or other parts of the body. A woman with previous breast cancer also has a three- to fourfold greater chance of developing another breast cancer in the opposite breast. In women who have been treated for breast cancer with breast conservation therapy (BCT), recurrence of cancer within the treated breast may also occur.
Other breast conditions
Even though most women with fibrocystic breasts and its related breast symptoms do not have increased risk of developing breast cancer, the lumpy texture and density of the breasts may hamper early cancer detection by breast examination or by mammography. Sometimes, women with fibrocystic breast changes have to undergo breast biopsies (obtaining small tissue samples from the breast for examination under a microscope) to make certain that palpable lumps are not cancerous.
Breast biopsies sometimes may reveal abnormal, though not yet cancerous, cell changes (called atypical hyperplasia). Women with atypical hyperplasia of the breast tissue have about a four- to fivefold enhanced likelihood of developing breast cancer. Some other benign cell changes in breast tissue are also associated with a slight increase (one and a half to two times normal) in risk. These are termed hyperplasia of breast tissue without atypia, sclerosing adenosis, fibroadenoma with complex features, and solitary papilloma.
The common benign breast tumor known as a fibroadenoma, unless it has unusual features under the microscope, does not confer an increased cancer risk.
Breast cancer risks can be additive. For example, women who have first-degree relatives with breast cancer and who also have atypical hyperplasia of the breast tissue have a much higher risk of developing breast cancer than women without these risk factors.
Radiation therapy
Women with a history of radiation therapy to the chest area as treatment for another cancer (such as Hodgkin's disease or non-Hodgkin's lymphoma) have a significantly increased risk for breast cancer, particularly if the radiation treatment was received at a young age.
Hormonal factors
Women who started their menstrual periods before age 12, those who have late menopause (after age 55), and those who had their first pregnancy after age 30, or who have never had children have a mildly increased risk of developing breast cancer (less than two times the normal risk). Early onset of menses, late arrival of menopause, and late or no pregnancies are all factors that increase a woman's lifetime level of estrogen exposure.
Studies have confirmed that long-term use (several years or more) of hormone therapy (HT) after menopause, particularly estrogens and progesterone combined, leads to an increase in risk for development of breast cancer. This risk appears to return to normal if a woman has not used hormone therapy for five years or more. Similarly, some studies show birth control pills cause a small increased risk of breast cancer, but this risk also returns to normal after 10 years of nonuse. The decision whether to use hormone therapy or birth control pills involves weighing the risks versus the benefits and should be individualized after consulting one's doctor.
Lifestyle factors
Dietary factors such as high-fat diets and alcohol consumption have also been implicated as factors that increase the risk for breast cancer. Cigarette smoking, caffeine intake, antiperspirant use, bras, breast implants, miscarriages or abortions, and stress do not appear to increase the risk of breast cancer. It is important to remember that 75% of women who develop breast cancer have no risk factors other than age. Thus, screening and early detection are important to every woman regardless of the presence of risk factors.
Alcohol
The consumption of alcohol is associated with an increased risk of developing breast cancer, and this risk increases with the amount of alcohol consumed. Compared with nondrinkers, women who consume one alcoholic drink a day have a very small increase in risk. However, those who have two to five drinks daily have about one and a half times the risk of women who drink no alcohol.