What Is Breast Cancer

What Is Breast Cancer 2

What Is Breast Cancer 4

What Is Breast Cancer 5

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      Detailed Guide: Breast Cancer

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What Is It?

What Is Cancer?

What Is Breast Cancer?

What Are the Key Statistics for Breast Cancer?

Causes, Risk Factors and Prevention

What Are the Risk Factors for Breast Cancer? Do We Know

What Causes Breast Cancer?

Can Breast Cancer Be Prevented?

Early Detection, Diagnosis, Staging

Can Breast Cancer Be Found Early?

How Is Breast Cancer Diagnosed?

How Is Breast Cancer Staged?

Treating Breast Cancer

How Is Breast Cancer Treated?

Local Versus Systemic Therapy Surgical Procedures for Breast Cancer Chemotherapy Radiation Therapy Hormone Therapy Monoclonal Antibody Therapy with Trastuzumab (Herceptin®) Bisphosphonates High Dose Chemotherapy with Autologous Bone Marrow or Peripheral Blood Stem Cell Support Clinical Trials Breast Cancer Treatment by Stage Complementary & Alternative Methods More Treatment Information

Talking With Your Doctor

What Should You Ask Your Doctor About Breast Cancer?

What Happens After Treatment for Breast Cancer?

More Information

What's New in Breast Cancer Research and Treatment?

Additional Resources for Breast Cancer References

Detailed Guide:

What Is Cancer?

Cancer develops when cells in a part of the body begin to grow out of control. Although there are many kinds of cancer, they all start because of out-of-control growth of abnormal cells.

Normal body cells grow, divide, and die in an orderly fashion. During the early years of a person's life, normal cells divide more rapidly until the person becomes an adult. After that, cells in most parts of the body divide only to replace worn-out or dying cells and to repair injuries.

Because cancer cells continue to grow and divide, they are different from normal cells. Instead of dying, they outlive normal cells and continue to form new abnormal cells.

Cancer cells develop because of damage to DNA. This substance is in every cell and directs all activities. Most of the time when DNA becomes damaged the body is able to repair it. In cancer cells, the damaged DNA is not repaired. People can inherit damaged DNA, which accounts for inherited cancers. More often, though, a person's DNA becomes damaged by exposure to something in the environment, like smoking.

Cancer usually forms as a tumor. Some cancers, like leukemia, do not form tumors. Instead, these cancer cells involve the blood and blood-forming organs and circulate through other tissues where they grow.

Often, cancer cells travel to other parts of the body where they begin to grow and replace normal tissue. This process is called metastasis. Regardless of where a cancer may spread, however, it is always named for the place it began. For instance, breast cancer that spreads to the liver is still called breast cancer, not liver cancer.

Not all tumors are cancerous. Benign (noncancerous) tumors do not spread (metastasize) to other parts of the body and, with very rare exceptions, are not life threatening.

Different types of cancer can behave very differently. For example, lung cancer and breast cancer are very different diseases. They grow at different rates and respond to different treatments. That is why people with cancer need treatment that is aimed at their particular kind of cancer.

Cancer is the second leading cause of death in the United States. Half of all men and one third of all women in the United States will develop cancer during their lifetimes. Today, millions of people are living with cancer or have had cancer. The risk of developing most types of cancer can be reduced by changes in a person's lifestyle, for example, by quitting smoking and eating a better diet. The sooner a cancer is found and treatment begins, the better are the chances for living for many years.

Revised 02/06/2006

What Is Breast Cancer?

Breast cancer is a malignant tumor that has developed from cells of the breast. A malignant tumor is a group of cancer cells that may invade surrounding tissues or spread (metastasize) to distant areas of the body. The disease occurs almost entirely in women, but men can get it, too. The remainder of this document refers only to breast cancer in women. For information on breast cancer in men, see the American Cancer SocietyÂ’s document, "Breast Cancer in Men."

Normal Breast Structure

The female breast is made up mainly of lobules (milk-producing glands), ducts (milk passages that connect the lobules to the nipple), and stroma (fatty tissue and connective tissue surrounding the ducts and lobules, blood vessels, and lymphatic vessels).

Most breast cancers begin in the cells that line the ducts (ductal), some in the cells that line the lobules (lobular), and the rest in other tissues.

As in most tissues of the body, fluids are circulated by 2 main forms of drainage channels. The blood stream carries plasma, red blood cells, white blood cells, and platelets. Lymphatic vessels are like veins, except that they carry lymph instead of blood. Lymph is a clear fluid that contains tissue fluid and waste products and immune system cells (cells that are important in fighting infections). Lymph nodes are small bean-shaped collections of immune system cells that are found along lymphatic vessels. Cancer cells that enter lymphatic vessels can spread and begin to grow in lymph nodes.

Almost all lymphatic vessels in the breast connect to lymph nodes under the arm (axillary lymph nodes). Some lymphatic vessels connect to lymph nodes inside the chest (internal mammary nodes) and either above or below the collarbone (supra- or infraclavicular nodes).

Because there is no easy way to figure out whether or not breast cancer cells have gotten into the blood stream drainage channels (veins), doctors rely on a surrogate piece of information: whether or not cancer cells are in lymph nodes. If cancer cells are able to break into the lymphatic drainage system and then begin to grow, we know that there is a higher chance that the cells could have gotten into the bloodstream and therefore be carried off to another organ in the body. When breast cancer cells reach the axillary (underarm) lymph nodes, they may continue to grow, often causing the lymph nodes in that area to swell.

This is why it is important to find out if breast cancer has spread to your axillary lymph nodes when you are choosing a treatment. The more lymph nodes that are involved with the breast cancer, the more likely it is that the cancer will eventually be found in other organs as well. However, not all women with lymph node involvement develop metastases, and it is not unusual for a woman to have negative lymph nodes and later develop metastases.

Benign Breast Lumps

Most breast lumps are not cancerous, that is, they are benign. Still, many need to be biopsied (see below) to prove they are not cancer. Most lumps turn out to be fibrocystic changes. The term "fibrocystic" refers to fibrosis and cysts. Fibrosis is the formation of fibrous (or scar-like) tissue, and cysts are fluid-filled sacs. Fibrocystic changes can cause breast swelling and pain. This often happens just before a period is about to begin. Your breasts may feel nodular, or lumpy, and, sometimes, you may notice a clear or slightly cloudy nipple discharge.

Benign breast tumors such as fibroadenomas or papillomas are abnormal growths, but they are not cancer and cannot spread outside of the breast to other organs. They are not life threatening. But some benign breast conditions such as papillomas and atypical hyperplasia are important because women with these conditions have a higher risk of developing breast cancer. For more information see the section, "What Are the Risk Factors for Breast Cancer?" and the American Cancer Society document, "Noncancerous Breast Conditions."

Types of Breast Cancers

It is important to understand some of the key words used to describe different types of breast cancer. It is not unusual for a single breast tumor to be a combination of these types and to have a mixture of invasive and in situ cancer.

Adenocarcinoma: Nearly all breast cancers start in the ducts or lobules of the breast. Because this is glandular tissue, they are called adenocarcinomas, a term applied to cancers of glandular tissue anywhere in the body. The 2 main types of breast adenocarcinomas are ductal carcinomas and lobular carcinomas.

In situ: This term is used for the early stage of cancer, when it is confined to the immediate area where it began. Specifically in breast cancer, in situ means that the cancer remains confined to ducts (ductal carcinoma in situ) or lobules (lobular carcinoma in situ). It has not invaded surrounding fatty tissues in the breast nor spread to other organs in the body.

Ductal carcinoma in situ (DCIS): Ductal carcinoma in situ (also known as intraductal carcinoma) is the most common type of noninvasive breast cancer. DCIS means that the cancer cells are inside the ducts but have not spread through the walls of the ducts into the surrounding breast tissue.

About 20% of new breast cancer cases will be DCIS. Nearly all women diagnosed at this early stage of breast cancer can be cured. A mammogram is the best way to find DCIS early.

When DCIS is diagnosed, the pathologist (a doctor specializing in diagnosing disease from tissue samples) will consider whether an area of dead or degenerating cancer cells, called tumor necrosis, is present. If necrosis is present, the tumor is considered more aggressive. The term comedocarcinoma is often used to describe DCIS with necrosis.

Lobular carcinoma in situ (LCIS): Although not a true cancer, LCIS (also called lobular neoplasia) is sometimes classified as a type of noninvasive breast cancer, and this is why it is included here. It begins in the milk-producing glands but does not grow through the wall of the lobules.

Most breast cancer specialists think that LCIS itself does not usually become an invasive cancer, but women with this condition do have a higher risk of developing an invasive breast cancer in the same breast or in the opposite breast. For this reason, women with LCIS, in particular, should pay close attention to having regular mammograms (see below for guidelines).

Infiltrating (or invasive) ductal carcinoma (IDC): This is the most common breast cancer. It starts in a milk passage, or duct, of the breast, has broken through the wall of the duct, and invaded the fatty tissue of the breast. At this point, it can metastasize, or spread to other parts of the body through the lymphatic system and bloodstream. About 80% of invasive breast cancers are infiltrating ductal carcinomas.

Infiltrating (or invasive) lobular carcinoma (ILC): Infiltrating lobular carcinoma starts in the milk-producing glands, or lobules. Similar to IDC, it also can spread (metastasize) to other parts of the body. About 10% of invasive breast cancers are ILCs. Invasive lobular carcinoma may be harder to detect by a mammogram than invasive ductal carcinoma.

Inflammatory breast cancer: This uncommon type of invasive breast cancer accounts for about 1% to 3% of all breast cancers. It makes the skin of the breast look red and feel warm and gives the skin a thick, pitted appearance. Doctors now know that these changes are not caused by inflammation or infection, but by cancer cells blocking lymph vessels or channels in the skin.

Medullary carcinoma: This special type of infiltrating breast cancer has a rather well-defined, distinct boundary between tumor tissue and normal tissue. It also has some other special features, including the large size of the cancer cells and the presence of immune system cells at the edges of the tumor. Medullary carcinoma accounts for about 5% of breast cancers. The outlook, or prognosis, for this kind of breast cancer is better than for other types of invasive breast cancer. But these are often hard to distinguish from infiltrating ductal carcinoma and are treated the same way.

Mucinous carcinoma: This rare type of invasive breast cancer is formed by mucus-producing cancer cells. The prognosis for mucinous carcinoma is better than for the more common types of invasive breast cancer. Colloid carcinoma is another name for this type of breast cancer.

Paget disease of the nipple: This type of breast cancer starts in the breast ducts and spreads to the skin of the nipple and then to the areola, the dark circle around the nipple. It is rare, accounting for only 1% of all cases of breast cancer. The skin of the nipple and areola often appears crusted, scaly, and red, with areas of bleeding or oozing. The woman may notice burning or itching. Paget disease may be associated with in situ carcinoma or with infiltrating breast carcinoma. If no lump can be felt in the breast tissue and the biopsy shows DCIS but no invasive cancer, the prognosis is excellent.

Phyllodes tumor: This very rare breast tumor develops in the stroma (connective tissue) of the breast, in contrast to carcinomas, which develop in the ducts or lobules. Phyllodes (also spelled phylloides) tumors are usually benign but on rare occasions may be malignant.

Benign phyllodes tumors are treated by removing the mass and a narrow margin of normal breast tissue. A malignant phyllodes tumor is treated by removing it along with a wider margin of normal tissue, or by mastectomy. These cancers do not respond to the usual treatments for invasive ductal or lobular breast cancer. In the past, both benign and malignant phyllodes tumors were referred to as cystosarcoma phyllodes.

Tubular carcinoma: Tubular carcinomas are another special type of infiltrating breast carcinoma. It was named tubular because of the way the cells look under the microscope. Tubular carcinomas account for about 2% of all breast cancers and have a better prognosis than infiltrating ductal or lobular carcinomas.

Detailed Guide: Breast Cancer

What Are the Key Statistics for Breast Cancer?

Breast cancer is the most common cancer among women, except for nonmelanoma skin cancers. The chance of developing invasive breast cancer at some time in a woman's life is about 1 in 8 (13% of women). It is estimated that in 2006 about 212,920 new cases of invasive breast cancer will be diagnosed among women in the United States. At this time there are slightly over 2 million breast cancer survivors in the United States. Women living in North America have the highest rate of breast cancer in the world.

Carcinoma in situ (CIS) accounts for about 61,980 new cases each year. CIS is noninvasive and is the earliest form of breast cancer. Breast cancer also occurs in men. An estimated 1,720 cases of invasive breast cancer will be diagnosed in men in 2005.

Breast cancer incidence rates have continued to increase since 1980, although the rate of increase slowed in the 1990s, compared to the 1980s. Furthermore, in the more recent time period (1987-2000), breast cancer incidence rates have increased only in women aged 50 and older.

Breast cancer is the second leading cause of cancer death in women, exceeded only by lung cancer. The chance that breast cancer will be responsible for a woman’s death is about 1 in 33 (3%). In 2006, about 40,970 women and 460 men will die from breast cancer in the United States. Death rates from breast cancer have been declining. These decreases are believed to be the result of early detection and improved treatment.

Detailed Guide: Breast Cancer

What Are the Risk Factors for Breast Cancer?

A risk factor is anything that increases your chance of getting a disease, such as cancer. Different cancers have different risk factors. For example, exposing skin to strong sunlight is a risk factor for skin cancer. Smoking is a risk factor for cancers of the lung, mouth, larynx, bladder, kidney, and several other organs.

But having a risk factor, or even several, does not mean that you will get the disease. Most women who have one or more breast cancer risk factors never develop the disease, while many women with breast cancer have no apparent risk factors (other than being a woman and growing older). Even when a woman with breast cancer has a risk factor, there is no way to prove that it actually caused her cancer.

There are different kinds of risk factors. Some factors, like a person's age or race, can't be changed. Others are linked to cancer-causing factors in the environment. Still others are related to personal choices such as smoking, drinking, and diet. Some factors influence risk more than others, and your risk for breast cancer can change over time, due to factors such as aging or lifestyle.

Risk Factors You Cannot Change

Gender: Simply being a woman is the main risk factor for developing breast cancer. Although women have many more breast cells than men, the main reason they develop more breast cancer is because their breast cells are constantly exposed to the growth-promoting effects of the female hormones estrogen and progesterone, thus making breast cancer much more common in women than men. Men can develop breast cancer, but this disease is about 100 times more common among women than men.

Aging: Your risk of developing breast cancer increases as you get older. About 18% of breast cancer diagnoses are among women in their 40s, while about 77% of women with breast cancer are older than 50 when they are diagnosed.

Genetic risk factors: Recent studies have shown that about 5% to 10% of breast cancer cases are hereditary as a result of gene changes (mutations). The most common gene changes are those of the BRCA1 and BRCA2 genes. Normally, these genes help to prevent cancer by making proteins that keep cells from growing abnormally. However, if you have inherited either mutated gene from a parent, you are at increased risk for breast cancer.

See the section "Do We Know What Causes Breast Cancer?" for more information about genes and DNA. Women with an inherited BRCA1 or BRCA2 mutation have up to an 80% chance of developing breast cancer during their lifetime and at a younger age than those women who are not born with one of these gene mutations in their cells. Women with these inherited mutations also have an increased risk for developing ovarian cancer.

Other genes have been discovered that might also lead to inherited breast cancers. One of these is the ATM gene. ATM stands for ataxia-telangiectasia mutation. The gene is responsible for repairing damaged DNA. Certain families with a high rate of breast cancer have been found to have mutations of this gene. Another gene, the CHEK-2 gene, also increases breast cancer risk when it is mutated. Neither one of these genes, however, is a frequent cause of familial breast cancer.

Inherited mutations of the p53 tumor suppressor gene can also increase your risk of developing breast cancer, as well as leukemia, brain tumors, and/or sarcomas (cancer of bones or connective tissue). The Li-Fraumeni syndrome, named after the 2 researchers who described this inherited cancer syndrome, is a rare cause of breast cancer.

If you are considering genetic testing, it is strongly recommended that first you talk to a genetic counselor, nurse, or doctor qualified to interpret and explain these tests, before being tested. It is very important to understand and carefully weigh the benefits and risks of genetic testing before these tests are done. Testing is expensive and is not covered by some health plans. There is concern that people with abnormal genetic test results will not be able to get life insurance or that coverage may only be available at a much higher cost, but many states have passed laws that prevent insurance companies from denying insurance on the basis of genetic testing. To learn about your state, you can go to this nternet site --

http://www.ncsl.org/programs/health/genetics/ndishlth.htm
For more information, see our position statement on genetic testing or go to the National Cancer Institute site on genetic testing for breast cancer.

Family history of breast cancer: Breast cancer risk is higher among women whose close blood relatives have this disease. Your risk of developing breast cancer is increased if:

• You have 2 or more relatives with breast or ovarian cancer.

• Breast cancer occurs before age 50 in a relative (mother, sister, grandmother or aunt) on either side of the family. The risk is higher if your mother or sister has a history of breast cancer.

• You have relatives with both breast and ovarian cancer.

• You have 1 or more relatives with two cancers (breast and ovarian, or 2 different breast cancers).

• You have a male relative (or relatives) with breast cancer.

• You have a family history of breast or ovarian cancer and Ashkenazi Jewish heritage.

• Your family history includes a history of diseases associated with hereditary breast cancer such as Li-Fraumeni or Cowdens Syndromes.

Having 1 first-degree relative (mother, sister, or daughter) with breast cancer approximately doubles a woman's risk, and having 2 first-degree relatives increases her risk 5-fold. Although the exact risk is not known, women with a family history of breast cancer in a father or brother also have an increased risk of breast cancer. Altogether, about 20% to 30% of women with breast cancer have a family member with this disease.

Personal history of breast cancer: A woman with cancer in one breast has a 3- to 4-fold increased risk of developing a new cancer in the other breast or in another part of the same breast. This is different from a recurrence (return) of the first cancer.

Race: White women are slightly more likely to develop breast cancer than are African-American women. But African-American women are more likely to die of this cancer. Many experts now feel that the main reason for this is because African-American women have more aggressive tumors (see basal-like breast cancer, below). The reasons for this are not known. Asian, Hispanic, and Native American women have a lower risk of developing and dying from breast cancer.

Previous abnormal breast biopsy: Women whose earlier breast biopsies detected any of these changes have a slightly higher risk of breast cancer (1.5 to 2 times greater than other women):

• fibroadenoma with complex features

• hyperplasia without atypia

• sclerosing adenosis

• multiple papillomas

Atypical hyperplasia (ductal or lobular) increases a woman's breast cancer risk by 4 to 5 times.

Having a biopsy specimen diagnosed as fibrocystic changes without proliferative breast disease or fibroadenoma does not affect breast cancer risk.

Previous breast radiation: Women who as children or young adults have had radiation therapy to the chest area as treatment for another cancer (such as Hodgkin disease or non-Hodgkin lymphoma) are at significantly increased risk for breast cancer. Some reports found the risk to be 12 times normal risk. This varies with the age of the patient at the time of radiation. Younger patients have a higher risk. If chemotherapy was also given, the risk may be lowered if the chemotherapy stops ovarian hormone production.

Menstrual periods: Women who started menstruating at an early age (before age 12) or who went through menopause at a late age (after age 55) have a slightly higher risk of breast cancer.

Diethylstilbestrol (DES): In the 1940s through the 1960s some pregnant women were given diethylstilbestrol because it was thought to lower their chances of losing the baby. Recent studies have shown that these women have a slightly increased risk of developing breast cancer.

Lifestyle-Related Factors and Breast Cancer Risk

Not having children: Women who have had no children or who had their first child after age 30 have a slightly higher breast cancer risk. Having multiple pregnancies and becoming pregnant at an early age reduces breast cancer risk.

Oral contraceptive use: It is still not certain what part oral contraceptives (birth control pills) might play in breast cancer risk. Studies have suggested that women now using oral contraceptives have a slightly greater risk of breast cancer than women who have never used them. Women who stopped using oral contraceptives more than 10 years ago do not appear to have any increased breast cancer risk. When considering using oral contraceptives, women should discuss their other risk factors for breast cancer with their health care team.

Hormone replacement therapy: It has become clear that long-term use (several years or more) of hormone replacement therapy (HRT) after menopause, particularly estrogens and progesterone combined increase your risk of breast cancer. They may also increase your chances of dying of breast cancer.

If you still have your uterus (womb), doctors generally prescribe estrogen and progesterone (known as combined HRT). Estrogen relieves menopausal symptoms and delays osteoporosis (thinning of the bones that can lead to fractures). But estrogen can increase the risk of developing cancer of the uterus. Progesterone is added to help prevent this.

If you no longer have your uterus, estrogen alone can be prescribed. This is commonly known as estrogen replacement therapy (ERT). This probably does not increase the risk of breast cancer very much, if at all.

Several large studies, including the Women's Health Initiative (WHI), have found that there is an increased risk of breast cancer related to the use of combined HRT. The most recent results from the WHI found that not only did combined HRT increase breast cancer risk, but it also increased the likelihood that the cancer would be found at a more advanced stage. This is because it appeared to reduce the effectiveness of mammography, as more abnormal findings on mammograms were noted. A large study from the United Kingdom has now found that women who took the combined therapy were also more likely to die of breast cancer than women who didn't.

The risk of HRT appears to apply only to current and recent users, and a woman's breast cancer risk seems to return to that of the general population within 5 years of stopping HRT.

Estrogen alone (ERT) does not appear to increase the risk of developing breast cancer. In fact, a separate part of the large WHI study found that it may slightly decrease the risk (although it was linked to an increased risk of stroke).

At this time there appear to be few strong reasons to use hormone replacement therapy (combined HRT or ERT), other than possibly for the temporary relief of menopausal symptoms. In addition to the increased risk of breast cancer, the WHI found that combined HRT also increased the risk of heart disease, blood clots, and strokes, and did not have a beneficial effect on mental function or preventing Alzheimer's disease. It did lower the risk of colorectal cancer and osteoporosis, but this must be weighed against the possible harms, and with the understanding that there are other effective ways to prevent osteoporosis. And, as noted above, while ERT did not seem to have much effect on the risk of breast cancer, it did increase the risk of stroke.

The decision to use hormone replacement therapy after menopause should be made by the woman and her doctor after weighing the possible risks (including increased risk of heart disease, breast cancer, strokes, and blood clots) and benefits (relief of menopausal symptoms, reduced risk of osteoporosis), and considering each womanÂ’s other risk factors for heart disease, breast cancer, osteoporosis, and the severity of her menopausal symptoms.

Breast-feeding and pregnancy: Some studies suggest that breast-feeding may slightly lower breast cancer risk, especially if breast-feeding is continued for 1.5 to 2 years. Other studies found no impact on breast cancer risk.

The explanation of this may be that both pregnancy and breast-feeding reduce a woman's total number of lifetime menstrual cycles. This may be similar to the reduction of risk due to late menarche (start of menstrual periods) or early menopause, which also decrease the total number of menstrual cycles. One study concluded that having more children and breast-feeding longer could reduce the risk of breast cancer by half.

Alcohol: Use of alcohol is clearly linked to an increased risk of developing breast cancer. The risk increases with the amount of alcohol consumed. Compared with nondrinkers, women who consume 1 alcoholic drink a day have a very small increase in risk, and those who have 2 to 5 drinks daily have about 1½ times the risk of women who drink no alcohol. Alcohol is also known to increase the risk of developing cancers of the mouth, throat, and esophagus. The American Cancer Society recommends limiting your consumption of alcohol.

Obesity and high-fat diets: Obesity (being overweight) has been found to be a breast cancer risk in all studies, especially for women after menopause. Although your ovaries produce most of your estrogen, fat tissue produces a small amount of estrogen. Having more fat tissue can increase your estrogen levels and increase your likelihood of developing breast cancer.

The connection between weight and breast cancer risk is complex, however. For example, risk appears to be increased for women who gained weight as an adult but is not increased among those who have been overweight since childhood. Also, excess fat in the waist area may affect risk more than the same amount of fat in the hips and thighs. Researchers believe that fat cells in various parts of the body have subtle differences in their metabolism that may explain this observation.

Studies of fat in the diet have not clearly shown that this is a breast cancer risk factor. Most studies found that breast cancer is less common in countries where the typical diet is low in total fat, low in polyunsaturated fat, and low in saturated fat.

On the other hand, many studies of women in the United States have not found breast cancer risk to be related to dietary fat intake. Researchers are still not sure how to explain this apparent disagreement. Many scientists note that studies comparing diet and breast cancer risk in different countries are complicated by other differences (such as activity level, intake of other nutrients, genetic factors) that might also alter breast cancer risk.

More research is needed to better understand the effect of the types of fat eaten and body weight on breast cancer risk. But it is clear that calories do count and fat is a major source of these. A diet high in fat has also been shown to influence the risk of developing several other types of cancer, and intake of certain types of fat is clearly related to heart disease risk. We recommend you maintain a healthy weight and limit your intake of red meats, especially those high in fat or processed.

Physical activity: Evidence is growing that physical activity in the form of exercise reduces breast cancer risk. The only question is how much exercise is needed. In one study from the WomenÂ’s Health Initiative as little as 1.25 to 2.5 hours per week of brisk walking reduced a woman's risk by 18%. Walking 10 hours a week reduced the risk a little more.

Factors With Uncertain, Controversial, or Unproven Effect on Breast Cancer Risk

Antiperspirants: Internet e-mail rumors have suggested that chemicals in underarm antiperspirants are absorbed through the skin, interfere with lymph circulation and cause toxins to build up in the breast, and eventually lead to breast cancer. There is very little experimental or epidemiological evidence to support this rumor. Chemicals in products such as antiperspirants are tested thoroughly to ensure their safety. One small study recently found trace levels of parabens (used as preservatives in antiperspirants), which have weak estrogen-like properties, in a small sample of breast cancer tumors. However, the study did not look at whether parabens caused the tumors. This was a preliminary finding, and more research is needed to determine what effect, if any, parabens may have on breast cancer risk. On the other hand, a recent large epidemiological study found no increase in breast cancer in women who used underarm antiperspirants or shaved their underarms.

Underwire bras: Internet e-mail rumors and at least one book have suggested that bras cause breast cancer by obstructing lymph flow. There is no scientific or clinical basis for that claim.

Induced abortion: Several studies have provided very strong data that induced abortions have no overall effect on the risk of breast cancer. Also, there is no evidence of a direct relationship between breast cancer and spontaneous abortion (miscarriage) in most of the studies that have been published. Scientists invited to participate in a conference on abortion and breast cancer by the National Cancer Institute (February 2003) concluded that there was no relationship. A recent report of 83,000 women with breast cancer found no link to a previous abortion, either spontaneous (stillbirth) or induced.

Breast implants: Several studies have found that breast implants do not increase breast cancer risk although silicone breast implants can cause scar tissue to form in the breast. Implants make it harder to see breast tissue on standard mammograms, but additional x-ray pictures called implant displacement views can be used to more completely examine the breast tissue.

Environmental pollution: A great deal of research has been reported and more is being done to understand environmental influences on breast cancer risk. The goal is to determine their possible relationships to breast cancer.

Currently, research does not show a clear link between breast cancer risk and exposure to environmental pollutants, such as the pesticide DDE (chemically related to DDT), and PCBs (polychlorinated biphenyls).

Tobacco Smoke: Most studies have found no link between active cigarette smoking and breast cancer. Though active smoking has been suggested to increase the risk of breast cancer in some studies, the issue remains controversial.

An issue that continues to be an active focus of scientific research is whether secondhand smoke may increase the risk of breast cancer. Both mainstream and secondhand smoke contain about 20 chemicals that, in high concentrations, cause breast cancer in rodents. Chemicals in tobacco smoke reach breast tissue and are found in breast milk.

The evidence regarding secondhand smoke and breast cancer risk in human studies is controversial, at least in part because the risk has not been shown to be increased in active smokers. One possible explanation for this is that tobacco smoke may have different effects on breast cancer risk in smokers and in those who are just exposed to smoke.

A report from the California Environmental Protection Agency in 2005 concluded that the evidence regarding secondhand smoke and breast cancer is "consistent with a causal association" in younger, mainly premenopausal women. The 2006 US Surgeon General's report, The Health Consequences of Involuntary Exposure to Tobacco Smoke, concluded that there is "suggestive but not sufficient" evidence of a link at this point. In any case, women should be told that this possible link to breast cancer is yet another reason to avoid contact with secondhand smoke.

Night work: A few recent studies have suggested that women who work at night, for example, nurses on a night shift, have an increased risk of developing breast cancer. However, this increased risk has not yet been proven, and when further studies are conducted, this factor may be found to be unimportant.

Detailed Guide: Breast Cancer

Do We Know What Causes Breast Cancer?

Although many risk factors may increase your chance of developing breast cancer, it is not yet known exactly how some of these risk factors cause cells to become cancerous. A woman's hormones somehow stimulate breast cancer growth. Just how this comes about has not yet been worked out.

Researchers are beginning to understand how certain changes in DNA can cause normal breast cells to become cancerous. DNA is the chemical that carries the instructions for nearly everything our cells do. We usually resemble our parents because they are the source of our DNA. However, DNA affects more than our outward appearance.

Some genes (parts of DNA) contain instructions for controlling when our cells grow, divide, and die. Certain genes that promote cell division are called oncogenes. Others that slow down cell division, or cause cells to die at the right time, are called tumor suppressor genes. It is known that cancers can be caused by DNA mutations (changes) that "turn on" oncogenes or "turn off" tumor suppressor genes.

The BRCA genes (BRCA1 and BRCA2) are tumor suppressor genes. When they are mutated, they no longer function to suppress abnormal growth and cancer is more likely to develop. Certain inherited DNA changes can cause a high risk for developing cancer in people who carry these changes and are responsible for the cancers that run in some families.

Most DNA mutations related to breast cancer, however, occur in single breast cells during a woman's life rather than having been inherited. Acquired mutations of oncogenes and/or tumor suppressor genes may result from radiation or cancer-causing chemicals. So far, however, studies have not been able to identify any chemical in the environment or in our diets that is likely to cause these mutations, or a subsequent breast cancer. The cause of most acquired mutations remains unknown.

Women have already begun to benefit in several ways from recent advances in understanding the genetic basis of breast cancer. The section, "What Are the Risk Factors for Breast Cancer?" explains how genetic testing can identify some women who have inherited abnormal BRCA1, BRCA2, CHEK-2, or p53 tumor suppressor genes. These women can then take steps to reduce their risk of developing breast cancers and to monitor changes in their breasts carefully to find cancer at an earlier, more treatable stage.

Most breast cancers have several gene mutations that are acquired. That means that these mutations are not inherited. They develop as part of the cancer.

Tests to identify other acquired changes in oncogenes or tumor suppressor genes (such as p53) may help doctors more accurately predict the survival outcome of some women with breast cancer. But with the exception of the HER2 oncogene, these tests have not yet been shown to be useful in making decisions about treatment and are used only for research purposes.

Detailed Guide: Breast Cancer

Can Breast Cancer Be Prevented?

A woman at average risk for breast cancer might reduce her risk somewhat by changing those risk factors that can be changed. If you give birth to several children and breast-feed them for several months, avoid alcohol, exercise regularly, and maintain a slim body, you are decreasing your risk of getting breast cancer. Likewise, avoiding HRT after menopause will avoid increasing your risk. (See the section, "What Are the Risk Factors for Breast Cancer?".)

Other than these lifestyle changes, the most important action a woman can take is to follow early detection guidelines. Following the American Cancer Society's guidelines for early detection, as outlined in the section, "Can Breast Cancer Be Found Early?", will not prevent breast cancer but can help find cancers when the likelihood of successful treatment is greatest.

If you are a woman with a strong family history of breast cancer or with a known genetic mutation of a BRCA gene, there are things you can do to reduce your chances of developing breast cancer. We strongly recommend genetic counseling before any of these steps. It is important to know if your mutation is BRCA1 or BRCA2. BRCA1 cancers may not be prevented by tamoxifen or raloxifene.

Also, if you have had DCIS, LCIS, or biopsies that have shown premalignant or precancerous changes, you might also consider treatment to reduce your breast cancer risk.

Breast Cancer Risk Reduction With Tamoxifen, Raloxifene, or Other Medicines

The anti-estrogen drug tamoxifen has been used for several years to reduce the risk of recurrence in localized breast cancer and as a treatment for advanced breast cancer. (See the section, "How Is Breast Cancer Treated?".)

Results from the Breast Cancer Prevention Trial (BCPT) have shown that women at increased risk for breast cancer are less likely to develop the disease if they take tamoxifen. Women in the study were assigned to take either tamoxifen or a placebo pill for 5 years. After 7 years of follow-up, women taking tamoxifen had 42% fewer breast cancers than women who took the placebo, although there was no difference in the risk of death due to breast cancer. Thus far, tamoxifen is the only drug approved for use in reducing breast cancer risk in high-risk women. (For more information on the possible benefits and risks of tamoxifen, see the American Cancer Society document, "Medicines to Reduce Breast Cancer Risk?".)

Because tamoxifen has side effects that include increased risks of endometrial (uterine) cancer and blood clotting, every woman should consider the possible benefits and risks of tamoxifen before deciding whether or not it is right for her.

Like tamoxifen, raloxifene also blocks the effect of estrogen on breast tissue. In a study looking at raloxifene for preventing osteoporosis, researchers noticed that it too seemed to lower the risk of breast cancer.

A study comparing the effectiveness of the 2 drugs, called the Study of Tamoxifen and Raloxifene (STAR) trial, found that raloxifene reduced the risk of invasive breast cancer to the same degree as tamoxifen, although it didn’t have the same protective effect against non-invasive cancer (DCIS or LCIS). Raloxifene did, however, have lower risks of certain side effects such as uterine cancer and blood clots in the legs or lungs. For now, raloxifene is still being studied for use in reducing breast cancer risk.

Other drugs that are being studied as breast cancer preventive agents in postmenopausal women are aromatase inhibitors. These block the production of small amounts of estrogen that postmenopausal women normally make. But they have side effects such as causing joint pain and stiffness and bone loss, leading to a higher risk of osteoporosis.

New studies are under way using other drugs. Some studies have found that women who take aspirin or non-steroidal anti-inflammatory drugs such as ibuprofen have a lower risk of breast cancer. Similar drugs (called COX-2 inhibitors) are being tested to see if they can reduce the risk of breast cancer in women who are at a high risk for this disease. Recent studies have shown, though, that COX-2 inhibitors can raise the risk of heart attacks.

More clinical trials will be needed before doctors can be certain of the best way to prevent breast cancer in women at high risk for this disease.

All the drugs mentioned above are discussed below under hormonal treatment.

Preventive (Prophylactic) Mastectomy for Women With Very High Breast Cancer Risk

For the few women who are at very high risk for breast cancer, prophylactic mastectomy may be an option. The purpose of the surgery is to reduce the risk by removing both breasts before breast cancer is diagnosed. The reasons for considering this type of surgery may include one or more of the following risk factors:

• mutated BRCA genes found by genetic testing

• previous cancer in one breast, strong family history (breast
cancer in several close relatives)

• biopsy specimens showing lobular carcinoma in situ (LCIS)

There is no way to know ahead of time how this surgery will affect a particular woman. Some women with BRCA mutations will develop a fatal breast cancer early in life, and a prophylactic mastectomy before the cancer occurs might add many years to their life expectancy. Although most women with BRCA mutations develop breast cancer, some don't and these women would not benefit from the surgery.

Also, it is important to realize that while this operation removes nearly all of the breast tissue, a small amount remains. So although this operation markedly reduces the risk of breast cancer, a cancer can still develop in the breast tissue remaining attached to the skin after surgery. So far, this has been a rare problem.

Although women might develop breast cancer that can be found by mammography or breast exam and be treated and cured by mastectomy, these women still face a high risk of cancer in the remaining breast. Second opinions are strongly recommended before any woman makes the decision to have this surgery. The American Cancer Society Board of Directors has stated that "only very strong clinical and/or pathologic indications warrant doing this type of preventive operation." Nonetheless, after careful consideration, this might be the right choice for some women.

Although this document is not about ovarian cancer, it is important that women with a BRCA mutation recognize they have a high risk of developing ovarian cancer. Most doctors recommend that the ovaries be surgically removed once child bearing is complete.


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