Breast Cancer

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Breast cancer is a general term that encompasses many different types of cancers that originate within the breast. Like all cancers, breast cancer arises from the abnormal growth of cells. In most instances, these cells gather together to form one or more tumors in the breast. The exact type of breast cancer is determined by the location and the growth characteristics of the cancerous cells. About 1 in every 8 women will develop some type of breast cancer over her lifetime.

The different types of breast cancers are classified as either noninvasive or invasive. Noninvasive tumors, also known as in situ breast cancers, are not life-threatening, but can develop into the more serious invasive breast cancer if left untreated. With invasive cancers, the cancerous cells infitrate into the surrounding breast tissue. The cancerous cells can also break away and enter the bloodstream or lymph system. This is how breast cancer can spread, or metastasize, to other organs or locations in the body. If left untreated, invasive breast cancers can be life-threatening.

Each year, about 192,000 women and 1,900 men in the United States are diagnosed with invasive breast cancer. And each year, nearly 40,000 women and 440 men die from invasive breast cancer. For women, only skin cancer is more common and only lung cancer is more deadly. Thankfully, the statistics of breast cancer are improving. The occurrence of invasive breast cancer is decreasing in the United States and the prognosis is brightening. Today, nearly 90 percent of women diagnosed with invasive breast cancer survive five or more years following their treatment.

This section includes information on:

  • Need-to-know-anatomy
  • Causes
  • Risk factors
  • Genetic testing
  • Breast cancer types
  • Need-to-know Anatomy

    The human breast consists of lobules and ducts nestled in a mass of tissue and vessels known as the stroma. The lobules are tiny glands that can produce milk. The milk is transported from the lobules to the nipples in hollow tubes known as ducts. The stroma provides the structural framework for the breast that is made up of connective and fatty tissues, blood vessels, and lymphatic vessels.

    Lymphatic vessels are small tubes that transport lymph. Lymph is a clear fluid that carries disease-fighting white blood cells, which combat germs, cancer cells, tissue fluid, and waste products from the breast. These vessels connect to the lymph nodes located mainly in the underarm area known as axillary nodes, those near the breast bone known as internal mammary nodes, and those located above and below the collar bone, known as supraclavicular and infraclavicular nodes. The lymph nodes filter out the germs, cancer cells, and foreign substances from the lymph before it is discharged into the blood stream.

    During puberty, the development of the breast is controlled by hormones. In men, the hormones restrict the development of the breast to a small number of ducts, stroma, and a few, if any, lobules. Women develop many lobules during puberty that are arranged into groups known as lobes that resemble bunches of grapes. Each breast may contain 15 to 20 lobes that radiate from the nipple in much the same way that the petals of a flower radiate from its center. In women of childbearing age, the majority of breast consists of fibrous and glandular tissue. After menopause there is a decrease in estrogen production and this glandular tissue tends to be replaced by fatty tissue.


    Breast cancer starts with abnormal changes or mutations in the DNA of individual cells in the breast. The DNA contains the operating instructions for the cell, known as genes. When these instructions are jumbled, uncontrolled cell growth can occur and form a breast tumor. These cancer cells may travel in the lymphatic vessels of the breast to the lymph nodes into the bloodstream and metastasize to other organs or parts of the body.

    In 5 to 10 percent of the people with breast cancer, the changes in the DNA are inherited. Several different genetic abnormalities have been linked to breast cancer, the most common of which are defects in the genes breast cancer gene 1, or BRCA1, and breast cancer gene 2, or BRCA2. These genes normally inhibit or prevent the growth of cancer cells. People with changes in these genes are at a significant increased risk for breast cancer as well as ovarian cancer in comparison to the general population.

    For most people, the genetic changes that lead to breast cancer do not appear to be inherited but occur during their lifetime, which is known as sporadic breast cancer. Doctors do not know what causes the changes in the DNA that lead to breast cancer; it is likely a complex interaction of the environment (see risk factors) and a person's genetic makeup.

    Risk Factors

    Most people who develop breast cancer have no family history of breast cancer. Research shows that certain factors are linked with the disease. How these risk factors can cause the cells in some people to become malignant and form breast cancer is not fully understood. The risk factors that increase the likelihood of developing breast cancer include:

    Being female. Breast cancer is about 100 times more common in women than men.

    Age over 55 years. For women, age is the most significant risk factor. Nearly 2 in every 3 women who develop invasive breast cancer are 55 years of age or older.

    Precancerous condition. Women with lobular carcinoma in situ (LCIS) have a seven to 11 times greater risk of developing cancer in either breast. Atypical hyperplasia is associated with about four times greater risk of developing breast cancer over your lifetime.

    Personal history of breast cancer.

    Family history of breast cancer. If you have a mother, sister, or daughter with breast or ovarian cancer, you have a greater chance of being diagnosed with breast cancer. This risk is about twice as high if breast cancer was diagnosed in a first degree relative before the age of 50. Still, 70 to 80 percent of people diagnosed with breast cancer have no family history of the disease.

    Dense breast tissue. Dense breast tissue contains more glandular tissue whose presence increases the risk for breast cancer by about four times.

    Radiation treatments to the chest as a child or young adult. This risk is related to the person's age at the time of radiation. The highest risk is for individuals who received radiation between ages 10 and 30. This radiation exposure is associated with about a 20 percent lifetime risk for developing breast cancer.

    Obesity. The link between weight and breast cancer is complex. The risk seems to be higher for those who gained weight after menopause or during adulthood. Maintaining a healthy weight after menopause can decrease the risk of developing breast cancer.

    Increased number of lifetime ovulation cycles. Women who began menstruating before age 12, began menopause after 55, had their first child after age 35, or had no children are at an increased risk for breast cancer.

    Postmenopausal hormone therapy that combines estrogen and progesterone. The use of combination hormonal therapy after menopause for more than three to five years is associated with a 26 percent increase in the risk of breast cancer.

    Drinking alcohol. Research indicates that drinking two or more alcoholic drinks per day increases the likelihood of developing cancer one to one-and-a-half times over those who drink one glass or less of alcohol. The exact mechanism is not known but is thought to be due to an increase in estrogen formation.

    Treatment with DES. In the past, some pregnant women were given the drug DES (diethylstilbestrol) to lower their chances of a miscarriage. Recent studies have shown that these women and their daughters, who were exposed to DES while in the womb, have a slightly increased risk of developing breast cancer.

    Inherited genetic makeup. Several genetic conditions increase the risk of breast cancer. The most common gene mutations are BRCA1 and BRCA2. These genes can increase your risk of developing breast cancer up to 80 percent, but they don't make cancer inevitable.

    Genetic Screening

    Genetic screening is used to determine if a person carries the known genes that are linked to breast cancer. This information can help determine your risk for breast cancer and the appropriate level of prevention for yourself as well as for your children. Genetic screening is usually only warranted for about 2 percent of women in the United States who are at increased risk. Individuals with a strong family history of breast cancer that involves multiple women on either side of the family, or other cancers such as ovarian, colon, or prostate cancer, as well as individuals with a male family member diagnosed with breast cancer are candidates for genetic testing.

    Anyone interested in pursuing genetic testing should speak with a genetic counselor, nurse, or doctor qualified to explain the process and interpret the results of these tests before proceeding with the screening. Usually this discussion starts with a thorough assessment of an individual's risk based upon the personal and family medical history. The specific genetic test(s) that might be used as well as the accuracy of the test and the medical implications of a positive, negative, or ambiguous result should be discussed. The psychological effects of genetic testing on an individual's emotions, social relationships, finances, and medical choices should be included in this discussion along with the risks of passing a mutation to children. Another factor to consider is whether or not the procedure is covered by your insurance plan; genetic screening can be expensive. The benefits and risks of testing can be far-reaching and should be carefully considered before proceeding with genetic screening for breast cancer.

    Types of Breast Tumors

    This section includes information on:

    • Precancerous conditions
    • Noninvasive breast cancer
    • Common types of invasive cancers
    • Less common types of invasive breast cancer
    • Recurrent breast cancer
    • Precancerous Conditions

      There are several benign or non-cancerous breast tumors that are not true cancers but rather conditions that indicate an increased risk for developing breast cancer. The most common include lobular carcinoma in situ and atypical hyperplasia. These benign tumors need to be managed to prevent their progression into a breast cancer.

      Lobular carcinoma in situ (LCIS) is an area of abnormal tissue growth that is limited to the milk-producing lobules. It does not have a distinct feature, thus is difficult to detect on a mammogram. It is often discovered during a biopsy to evaluate an abnormal mammogram or breast change. Because these women have a 10 to 20 percent lifetime risk of developing an invasive cancer, it's important that women with LCIS develop a strategy for managing LCIS with their physician.

      Management options for LCIS include observation with yearly mammograms and exams; treatment with anti-estrogen therapy such as tamoxifen or raloxifene, both of which have been shown to be effective in reducing the risk of developing into cancer; or preventive mastectomy. Women who have a strong family history of breast cancer or genetic risk and develop LCIS may want to consider a preventive mastectomy. Women with LCIS may want to discuss the risks and benefits of anti-estrogen medications or preventive mastectomy with their doctor in light of their medical and family history and personal values to develop their management strategy.

      Atypical hyperplasia is another precancerous condition that can develop into a carcinoma in situ. This condition is characterized by growth of abnormal cells. This typically occurs in the duct as atypical ductal hyperplasia (ADH) but can also develop in the lobule of the breast as atypical lobular hyperplasia (ALH). If you've been diagnosed with atypical hyperplasia, your risk for developing breast cancer has increased by about four times that of the general population. Your doctor may recommend surgery to excise the precancerous tissue, followed by more frequent breast cancer screening and use of the anti-estrogen medications tamoxifen or raloxifene to help prevent breast cancer in the future. Women with atypical hyperplasia will need to talk with their doctor about the risks and benefits of the medications and develop a management strategy that suits their individual situation.

      Noninvasive Breast Cancer

      Ductal carcinoma in situ (DCIS), the most common type of non-invasive breast cancer, is diagnosed in about 62,000 women each year. DCIS is contained entirely within the ducts and has not spread out of the milk duct or into the tissue of the breast. As the earliest form of breast cancer, DCIS is typically found during routine mammograms. The mammogram features include calcifications that look irregular and faint and tend to cluster in one area. About 1 of every 5 breast cancers is DCIS. Although it is not considered life-threatening, DCIS is important to treat because some of these tumors can develop into an invasive cancer.

      Common Types of Invasive Cancers

      Invasive (infiltrating) ductal carcinoma (IDC) is the most common type of breast cancer and accounts for nearly 8 of every 10 breast cancers. As a carcinoma, it begins in the cells that line a structural element of the body, in this case, the duct. The cells break through the lining and the wall of the duct and invade the tissue of the breast. Once in the tissue, the cancer can be carried to the lymph nodes and metastasize to the other parts of the body.

      Invasive (infiltrating) lobular carcinoma (ILC) starts in the milk-producing glands or the lobules. ILC is the second most common type of invasive cancer and accounts for almost 1 out of 10 invasive breast cancers. It typically develops later in women, usually striking in the early 60s. It can be difficult to detect, especially in dense breast tissue, and can metastasize to other parts of the body.

      Less Common Types of Invasive Breast Cancer

      Inflammatory breast cancer (IBC) is diagnosed in 1 to 3 percent of the individuals with breast cancers. Usually the cancer cells do not form a discrete tumor but block the lymphatic vessels in the breast. As a result, the breast becomes red and swollen and may be warm. The breast may also look like the peel of an orange with pitting or ridges. IBC develops rapidly and tends to have a higher chance of metastasizing and thus a worse outlook than typical invasive ductal or lobular cancers.

      Triple-negative breast cancer is called that because it is comprised of cells that lack both estrogen receptors and progesterone receptors and do not have an excess of the HER2 protein on their surfaces. These characteristics make the tumors more challenging to treat effectively. They will not respond to hormone therapy. Triple-negative breast cancers tend to grow faster and spread more quickly than most other types of breast cancer.

      Mixed tumors contain a variety of cell types, such as invasive ductal cancer combined with invasive lobular breast cancer. These cancers are treated as an invasive breast cancer.

      Medullary carcinoma accounts for about 3 to 5 percent of all breast cancers. These cancer cells are large and the boundary between normal tissue and the tumor is well-defined and lined with immune cells. These characteristics make medullary cancer easier to treat effectively.

      Metaplastic carcinoma is a very rare type of invasive breast cancer. These tumors include cells that normally are not found in the breast, such as ones that look like skin cells or cells that make bone.

      Mucinous carcinoma or colloid carcinoma is a rare type of invasive breast cancer that is formed by mucus-producing cancer cells. The prognosis for mucinous carcinoma is usually better than for the more common types of invasive breast cancer.

      Paget's Disease accounts for 1 percent of female breast cancers and is slightly more prevalent in men. The cancer begins in the ducts of the breast and usually extends into the skin of the nipple and the dark skin around the nipple, known as the areola. Only in rare cases is the disease limited to the nipple; it is usually associated with an underlying invasive ductal breast cancer.

      Tubular carcinomas account for about 2 percent of all breast cancers. When viewed under a microscope, the cell of the cancer appears tubular. Tubular carcinoma tends to have a better prognosis than most breast cancers.

      Papillary carcinomas are made up of small, finger-like groups of cells when viewed under the microscope. These tumors represent less than 1 to 2 percent of all breast cancers and can be either noninvasive or invasive. Most often, intraductal papillary carcinoma or papillary carcinoma in situ is noninvasive and sometimes considered a subtype of ductal carcinoma in situ (DCIS). More rarely, the tumor is invasive. When invasive, the tumors are treated like invasive ductal carcinoma, although the outlook is likely to be better.

      Adenoid cystic carcinomas or adenocystic carcinomas make up less than 1 percent of all breast cancers. They rarely spread to the lymph nodes or metastasize to distant parts of the body. As such they tend to have a very good prognosis.

      Phyllodes tumor, also known as phylloides tumor or cystosarcoma phyllodes, is a very rare breast tumor that develops in the stroma of the breast. These tumors are usually benign but on rare occasions may be malignant. Phyllodes tumors are treated surgically by removing the tumor along with a margin of normal breast tissue or a mastectomy.

      Angiosarcoma is an extremely rare complication of breast radiation therapy that can develop about five to 10 years after radiation. Angiosarcoma can also occur in the arm of women who develop swelling of the arm as a result of lymph node surgery or radiation therapy to treat breast cancer.

      Recurrent Breast Cancer

      Although breast cancer treatment is aimed at eliminating all cancer cells, a few may survive. These undetected cancer cells may multiply, becoming recurrent breast cancer. It may take months or years after the initial treatment for recurrent cancer to develop.

      Recurrent breast cancer may come back in the same place as the original tumor, known as local recurrence or in-breast recurrence. If the cancer returns to around the chest wall or underarms, it is known as regional recurrence. If the cancer has spread to other areas, typically the bones, liver, or lungs, it is known as metastatic breast cancer.

      Last reviewed on 3/28/10

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