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Definition: breast cancer from Dictionary of Medical Terms

a malignant tumour in a breast

Summary Article: Breast Cancer
From Encyclopedia of Cancer and Society

BREAST CANCER IS a major public health problem in the developed world. It is the most common cancer among U.S. women and makes up a significant portion of illness, healthcare expenses, and loss of life. One in eight women is expected to develop breast cancer in her lifetime. Factors associated with increased breast cancer risk include family history of the disease, higher number of lifetime menstrual periods, and inadequate physical activity; generally, the disease is thought to result from a complex combination of genetic and lifestyle factors. One key to reducing the burden of breast cancer is to detect the disease at its precancerous or early cancerous stages. Tools for early detection include mammography, imaging, and self-examinations.

Studies suggest that breast self-exams lead to increased follow-up of noncancerous masses, and do not increase breast cancer death rates.

The benefits of screening for early detection need to be balanced against the risks of increased anxiety among women whose screening results may ultimately turn out to be negative. Over recent decades, better treatment options for breast cancer have improved the outcome for patients. The promising outlook for breast cancer is due in part to breast cancer advocacy, which grew immensely at the end of the 20th century. Community involvement has increased awareness, support, and research funding for this common and deadly disease.

In 2007, over 178,000 women in the United States are expected to become affected with breast cancer, representing one-fourth of all cancers in women. Approximately 125 women per every 100,000 women are diagnosed with breast cancer annually. The number of new breast cancer cases increased rapidly throughout the 1980s, and since then has risen only slightly. This is likely to be a result of increased screening in the 1980s followed by the use of novel tools for early detection.

Despite increasing numbers of new diagnoses, early detection and improved treatments held the number of deaths attributed to breast cancer among women constant until 1990. Following this time, deaths due to breast cancer decreased substantially. The American Cancer Society reports that between 1990 and 2003, deaths from all types of cancers in women decreased, and 40 percent of this decline was due to reductions in breast cancer deaths.

Over 40,000 U.S. women are expected to die from breast cancer in 2007, approximately 25 women per every 100,000. The disease is currently the second-most common cause of cancer deaths (second to lung cancer), representing an estimated 15 percent of all deaths due to cancer in women. However, among women age 20–60, breast cancer is the most common cause of cancer death; African-American women are estimated to have the highest rates of breast cancer deaths compared to other women.


Although we have learned much about a variety of factors that may influence the development of breast cancer, the true “cause” of breast cancer remains unknown. It is likely that breast cancer results from a combination of genetic and nongenetic factors. Thus, a woman who is at increased risk due to disease in her family may be able to modify this risk with changes in lifestyle factors, such as increasing her frequency of exercise.

Epidemiologic researchers conducting studies of large numbers of women compare characteristics of those who do and who do not develop breast cancer and have found some consistent results. Some risk factors are unfortunately not modifiable. These include being female (women at much higher risk), being white (African-American, Asian, Hispanic, and American Indian women have lower rates), increasing in age (older women more likely to develop the disease), and having affected relatives (having a mother, sister, or daughter with breast cancer about doubles risk). In addition, starting periods at an early age and entering menopause at a later age increase a woman’s risk of breast cancer; this is thought to be due a longer lifetime exposure to estrogens.

Other factors related to the risk of developing breast cancer may be considered modifiable. These include childbearing (women pregnant at an early age and pregnant more than one once are at a lower risk), breast-feeding (women with children who breast-feed seem to be at reduced risk), exercise (physically active women are at lower risk), avoiding alcohol (drinking up to five drinks a day may increase risk), and maintaining lower body weight (children with large weight gain may be at increased risk of later breast cancer and women who are obese after menopause are at increased risk).

There are also more complex, modifiable factors that should be considered in consultation with a physician. Hormone replacement therapy, specifically the use of estrogens combined with progesterone, after menopause has been shown to increase breast cancer risk. A woman’s use of oral contraceptives within the last decade may increase risk as well. There are also medical conditions associated with increased risk including radiation treatment in the chest area, abnormal breast biopsy, and certain formerly used hormonal treatments such as diethylstilbestrol (DES).

A physician should be consulted about the risks and benefits of medical treatments that may lead to modified breast cancer risk later in life.

Less common factors may also influence a woman’s breast cancer risk. Studies are under way examining specific environmental pollutants that may influence risk at very high doses; however, no results to date are clear-cut. Approximately 7 percent of all breast cancer cases are thought to be due to particularly genetic changes passed down in families. A portion of these truly familial cases are due to changes in the genes, BRCA1 and BRCA2. Changes, or mutations, in these genes lead to an approximate 80 percent chance of developing breast cancer. While the search is under way for similar genes, and for genes conferring more modest increases in risk, it is likely that modifiable factors play a role even among families with these high-risk genes.


Like other cancers, the burden of breast cancer in terms of medical complications, expense, and, most important, death can be reduced if the disease is detected at an early stage; for example, before it has spread to other organs in the body. Early detection of breast cancer can be attained by routine population screening and by easy access to care when any symptoms first develop, assuming symptoms are recognized by the woman experiencing them.

There has been great debate in the recent decade about the utility of monthly breast self-exams. One of the potential harms from breast cancer screening comes from false positive findings leading to unnecessary further testing and anxiety. Several studies, including a large randomized trial in China, suggest that breast self-exams lead to increased follow-up of noncancerous masses and overall, do not increase breast cancer death rates.

The traditional approach to breast cancer detection is an annual physical examination by a physician. Many medical organizations, including the American Cancer Society and the American College of Radiology recommend annual screening mammograms for women starting at age 40. Screening mammograms are X-rays of the breasts (generally two for each breast) done in women with no signs or symptoms of breast cancer in order to find very early stages of breast cancer before they can be found on a clinical exam. It is generally agreed that patients between age 40 and 50 years should be screened every 12–24 months. There have been several randomized studies showing the efficacy of annual mammographic screening in reducing breast cancer rates by about 20–30 percent in women after age 50. The benefit of an annual screening mammography in women age 40 to 50 or over 70 years is less clear. It is important to note that breast exams performed by clinicians with proper technique can detect up to 5 percent of cancers not picked up by mammograms.

One form of screening mammography uses digital mammograms (as opposed to standard film mammograms) wherein images are captured as in film mammography and then digitally manipulated for clarity. Digital mammography is preferred in women with denser breast tissue; dense breast tissue is mainly seen in women who have not yet entered or are in the midst of menopause. Digital mammography systems are two to four times more expensive than film mammography systems. Some institutions use computer-aided interpretation of mammography, although the benefits of computer interpretations considering substantial increases in cost remain to be proven.

Other means of detecting breast cancers are used to complement these methods. Ultrasound of the breast complements a mammogram in evaluating lumps detected by physical examination and can be useful in following up abnormal mammogram findings and is relatively inexpensive. Magnetic resonance imaging (MRI) is a technique that enables the diagnosis of breast cancer that can’t be seen in mammograms in up to 10 to 18 percent of cases. An MRI can be used to identify multiple areas of cancer in the same breast and define the extent of cancer. An MRI of the breasts is increasingly used as a screening procedure especially in high-risk women (such as those with BRCA1 or BRCA2 gene mutations) and in women with dense breast tissue. Because an MRI is expensive, requires injection of dye, has a lower specificity leading to increase rate of follow-up invasive procedures, screening MRI is not advised in average risk women.


A biopsy of any lump in the breast or a suspicious area on a mammogram is performed using a needle to draw cells from the lump and examine them under a microscope. Cancer diagnosis is then established. At diagnosis, approximately 60 percent of breast cancers are localized (confined within the breast), 30 percent are regionally spread (for example, to nearby lymph nodes), and 10 percent have metastasized (for example, to the liver). African-American women tend to be diagnosed at a more advanced stage, consistent with increased rates of breast cancer death in this group and indicative of fast-growing disease. Two types of breast cancer can be diagnosed: ductal carcinoma in situ (DCIS) is diagnosed if the cancer has not invaded outside the mammary ducts, and invasive cancer is diagnosed when the cancer has spread outside the milk ducts.

When a breast cancer is diagnosed, the staging process begins, involving extensive testing to assess the extent of disease within the body. Medical history, physical examinations, chest X-ray, and blood tests are used as staging tests. If any of these tests are abnormal, then a bone scan (injection of a radionuclide substance intravenously and imaging the whole skeleton), computed tomography (CT) scan or a Positron emission tomography (PET) scan are obtained as needed. Some of these tests are very costly and are therefore used only when specially indicated.

Recent data suggest that, on average, 89 percent of women diagnosed with breast cancer survive five years or more. Women diagnosed with Stage I breast cancers (tumors less than 2 centimeters, no lymph node involvement) can have an overall 10-year survival (proportion of patients living 10 years following diagnosis) of up to 95 percent, women diagnosed at Stage II (less than 2 centimeters with or without lymph node involvement) have an average 10-year overall survival of up to 80 percent, and those with Stage III disease (less than 5 centimeters or fixed tumor or several SLNs involved or with inflammatory changes) have 10-year overall survival of up to 50 percent with modern treatments.


Women with early stage breast cancer typically undergo surgery. Mastectomy (removal of entire breast) and breast conservation surgery (smaller surgery focused on limited area using a wide local excision or lumpectomy) confer similar prognosis. Sentinel lymph node (SLN) sampling is routinely done during these surgeries, which involves the removal of the lymph node nearest to the affected area in the breast. The SLN is examined for the presence of cancer cells, and if the SLN is positive for cancer metastasis, then a full dissection of auxiliary lymph nodes is performed. Tumors that are removed in surgery are tested for estrogen receptor (ER) and progesterone receptor (PR) status, which indicates the presence of these proteins in the nuclei of the cancer cells.

Following surgery, subsequent treatments may include radiation treatment, chemotherapy, or hormonal therapy depending on the size of tumor, lymph node involvement, type of initial surgery, menopausal status, and ER/PR status. Patients with breast-conserving surgery undergo postoperative radiation therapy to prevent local recurrence of cancer. Currently, the standard radiation therapy is delivered over a period of approximately five weeks. Finding transportation to and from a radiation facility can be a financial burden for many patients.

Generally, for ER and PR positive tumors, hormonal therapy such as tamoxifen or aromatase inhibitors (which block adrenal gland production of estrogen) give maximum benefit in women who have gone through menopause. Even in premenopausal women, the hormonal therapy with removal or suppression of the ovaries may be of benefit.

In selected patients with DCIS and ER and PR positive tumors, tamoxifen is prescribed for five years to prevent local recurrence and the prevention of a new breast cancer in lieu of or in addition to radiation. These treatments can prolong a patient’s life by anywhere from 20–40 percent in Stage II and III patients.

For advanced cancers (large tumors and lymph node positive tumors), additional chemotherapy is recommended. The cost of chemotherapy further increases because patients need to receive growth factors to boost white blood cell count and/or red blood cells to facilitate timely treatment. Recently, herceptin, an antibody to treat certain aggressive breast cancers has been approved to be used along with chemotherapy. This is an expensive treatment requiring patients to return to clinic at least every three weeks for a whole year.

The American Cancer Society provides navigators for newly diagnosed patients to help them through the process of treatment and accessing resources in society. A mentor program links current patients with survivors to provide one-on-one support—for example, accompanying patients to a doctor’s visit to help them ask the right questions.


Both hormonal therapy and chemotherapy can cause significant side effects including hot flashes, severe joint pain, and nerve damage requiring further interventions that can be costly. Patients without insurance may not be able to afford cancer treatments and supportive services.

Lymphedema can occur postoperatively, in which excess fluids builds up in certain tissues and organs; lymphedema can adversely affect quality of life and decrease productivity at work. Fortunately, surgical advances removing only selected (rather than all) lymph nodes have reduced the burden of this condition.

The cost of breast cancer to patients and society including genetic testing, screening tests, and treatment of established cancer extends to follow-up testing to detect cancer recurrence. Randomized studies have shown that the majority of breast cancer recurrence is detected by a detailed history and physical exam with annual liver chemicals, mammogram, and chest X-ray monitoring picking up other recurrences. Expensive scans such as CT scans, PET scans, bone scans, and tumor markers in the blood are not currently recommended when following breast cancer survivors.

For breast cancer that has recurred or spread to other organs, there is no cure. However, these patients can live three or four additional years and be on continuous cancer treatments. Newer drugs such as antibody treatments offer more promise, but costs can be prohibitive with several thousand dollars per monthly treatment, mostly borne by insurance carriers and Medicare. Many of these patients continue to be productive citizens and view life differently following their diagnosis.

Breast cancer survivors have noncancer issues to deal with as well. Having a mastectomy can be a life-changing event for many patients. Patients may be distraught by the loss of a breast and lose their self-image. Reconstruction of the breast has given hope and solace to women who choose to undergo plastic surgery; insurance companies have recently recognized that this is an important aspect of a breast cancer patient’s recovery and currently cover the costs associated with this operation.

Young women thrown into early menopause by chemotherapy and anti-estrogen therapy may suffer from low libido and dry vagina, which can interfere with sexual relations and emotional relationships with partner. Belonging to survivor groups has been helpful to many women coping with these issues.


Women have proven that they carry a powerful voice. In the last half-century, breast cancer awareness has exploded. The month of October has been designated as Breast Cancer Awareness Month in the United States. Pink ribbons symbolizing breast cancer awareness are worn by patients, relatives, friends, and caregivers to remind people to go in for mammograms and contribute to breast cancer research funds. Major retailers such as Estée-Lauder and the Avon Foundation contribute a portion of their profits to breast cancer research.

Breast cancer survivors have lobbied and obtained reimbursement for breast reconstruction. Survivors attend national research meetings and conferences and their opinions are heard and incorporated into clinical trials.

The Susan G. Komen Foundation is a successful organization started by the sister of a breast cancer patient. It sponsors annual events throughout the nation to raise hundreds of thousands of dollars to fund major research. Breast cancer advocacy groups such as this and the National Breast Cancer Coalition have paved the way for other cancer groups to be powerful advocates. However, much work remains to prevent and cure breast cancer; ongoing research with community involvement is essential to achieve this goal.

  • Breast Cancer and Pregnancy; Breast Cancer, Male; Europa Donna the European Breast Cancer Coalition; National Alliance of Breast Cancer Organizations; Screening (Cervical and Breast and Colon Cancers).

  • L. C. Hartmann; C. L. Loprinzi, eds., Mayo Clinic Guide to Women’s Cancer (Mayo Clinic Health Information, 2005).
  • A. Jemal et al., “Cancer Statistics, 2007,” Cancer Journal for Clinicians (2007).
  • Susan Love; Karen Lindsay, Dr. Susan Love’s Breast Book (Da Capo Lifelong Books, 2005).
  • Ellen L. Goode, Ph.D., M.P.H.

    Prema P. Peethambaram, M.D.
    Mayo Clinic College of Medicine
    Copyright © 2007 by SAGE Publications, Inc.

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