Facts on Breast Cancer Causes, Risk Factors, and Types

Breast cancer facts

  • Statistics indicate that breast cancer affects over 230,000 women each year in the U.S.
  • Risk factors for developing breast cancer include female gender, age, certain inherited genetic mutations, and personal or family history of the condition.
  • Awareness of the importance of breast cancer screening can help ensure that tumors are identified at an early, treatable and more curable stage.
  • Common breast cancer symptoms and signs may include a lump in the breast, nipple discharge, and breast pain.
  • Most breast cancers are of the infiltrating ductal type.
  • Ductal carcinoma in situ (DCIS) is a form of ductal cancer that consists of atypical cells that have not spread beyond the ducts of the breasts into the adjacent breast tissue.
  • Because DCIS is not an invasive cancer, it is highly curable.
  • Inflammatory breast cancer is an uncommon, aggressive form of the disease.
  • Therapy for breast cancer depends partially upon the thr presence or abscence of by the hormone receptors and the HER2 protein in and on the cancer cells.
  • Surgery is a mainstay for diagnosis and treatment for breast cancer. Other treatments can include radiotherapy, chemotherapy, hormone therapy, and targeted therapy.
  • Survival rates for breast cancers diagnosed in the early stages are excellent.
  • Sentinel lymph node biopsy is a technique to determine whether a breast cancer has spread to the nearby lymph nodes.

What is breast cancer?

Breast cancer is called a malignancy in which abnormal cells arise in the breasts. In invasive types of breast cancer, these cells both appear abnormal and can invade into adjacent tissues in the breast and can spread, or metastasize, to other parts of the body. Breast cancer affects both men and women, although it is far more common in women. Each year, over 230,000 women in the U.S. are diagnosed with breast cancer, and about 40,000 women die from the disease every year. Male breast cancer accounts for about 1% of all breast cancers. This article focuses on breast cancer in women.

What are the risk factors for breast cancer?

The strongest risk factors for breast cancer are female sex and age. As mentioned above, breast cancer is far more common in women. However, men can also get breast cancer, but it is 100 times more common in women than in men. The risk of breast cancer increases with age, and breast cancer incidence rates are highest in women over 70 years of age. Only about 5% of women in the U.S. who are diagnosed with breast cancer are under 40 years old.

Family history and genetics are also risk factors. A woman is more likely to develop breast cancer if she has immediate family members who are affected. It is also possible to inherit gene mutations that increase the risk of breast and other cancers. Inherited mutations, however, account for only 5% to 10% of all breast cancers. BRCA1 and BRCA2 genetic mutations are associated with a markedly increased risk of breast cancer. Other genetic mutations have also been linked to an increased incidence of breast cancer.

A personal history of breast cancer increases a woman's risk of developing another breast cancer. A woman is also at increased risk if she has had Hodgkin's disease or other cancers. Having dense breasts (a greater proportion of glandular and connective tissue in the breasts relative to fat) means that a woman has a four- to five-fold increase in risk for breast cancer. Certain benign breast conditions may also increase a woman's risk (for example, a typical hyperplasia, a condition in which abnormal cells proliferate within the breast ducts).

Radiation treatment during youth, for example, chest radiation for treatment of another cancer, increases a woman's risk of breast cancer later in life.

Not having given birth or having given birth to a first child after the age of 35 are associated with moderate increases in breast cancer risk. Overweight and obesity after menopause also increase risk. Having begun menstruating before age 12 or having reached menopause after age 55 are associated with slight increases in breast cancer risk, likely because of the longer duration of estrogen exposure. Current or recent use of postmenopausal hormone therapy or birth control pills seems to slightly raise a woman's risk of breast cancer.

Both breastfeeding (for 1 year, cumulatively) and getting exercise (in postmenopausal women) seem to slightly lower the risk of breast cancer.


A lump in the breast is almost always cancer. See Answer

What causes breast cancer?

Breast cancer, like all cancers, is caused when changes within a cell (malignant transformation) cause it to acquire the ability to grow in an uncontrolled way. Normal mechanisms fail to check the growth of cells, and a population of malignant cells arises that has the capability to invade normal tissues and spread within the body. Cancers likely arise due to a series of mutations with cellular genetic material, and there is no one risk factor that is exclusively responsible for causing breast cancer. As with other cancers, a combination of genetic and environmental influences are likely involved to cause breast cancers.

What are the different types of breast cancer?

Breast cancer can be described as invasive or in situ. Invasive breast cancers are tumors that have spread beyond the ducts or lobules of the breast and have begun to invade normal tissues.

In situ breast cancers -- ductal carcinoma in situ (DCIS) or lobular carcinoma in situ (LCIS) -- are considered to be noninvasive forms of breast cancer. In these conditions, abnormalities in the cells have caused proliferation of atypical cells, but these cells have not spread beyond the ducts or lobules of the breast.

DCIS is currently an area of controversy in the breast cancer field. The risk in DCIS management is that if inadequately treated, then DCIS can recur. When it does, half the tie the recurrence shows evidence of invasive cancer, which is far more dangerous because it can spread. However, many cases of DCIS will never become invasive, and after excision of the abnormal areas, most cases of DCIS do not recur. However, there remains the possibility that simple excision of DCIS is not sufficient to prevent recurrence in some women, so additional treatment with both surgery and radiation therapy is often given. Currently, studies are under way in an attempt to identify which cases of DCIS are most likely to become invasive and which cases will follow a more indolent course.

Among invasive breast cancers, about 80% arise in cells of the ducts and are known as invasive ductal carcinomas. Another 10% arise in the milk glands or lobules and are termed invasive lobular carcinoma. The remaining breast cancers are made up of less common types of cancer, including Paget's disease of the nipple, a type of cancer that affects cells beneath the nipple. Inflammatory breast cancer (IBC) is an uncommon and very aggressive kind of cancer that makes up 1%-5% of breast cancers. In inflammatory breast cancer, the cancer cells block lymph vessels in the skin of the breast. The breast often appears swollen and red, or "inflamed." Combinations of different cancer types are also possible.

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Medically reviewed by Jay B. Zatzkin, MD; American Board of Internal Medicine with subspecialty in Medical Oncology


American Cancer Society. "Breast Cancer Overview." <http://www.cancer.org/cancer/breastcancer/overviewguide/>.

Stopeck, Alison T. "Breast Cancer." Medscape.com. Sept. 16, 2014. <http://emedicine.medscape.com/article/1947145-overview#aw2aab6b2b7>.

United States. National Cancer Institute. "Breast Cancer." Sept. 26, 2012. <http://www.cancer.gov/cancertopics/wyntk/breast>.