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Breast Cancer

Last Updated: Mar 1, 2019


Breast cancer occurs when cells in the breast multiply out of control, forming an abnormal mass (tumor) that tends to invade surrounding tissues. Because cancer cells lactiferous ducts (shown in breast cross-section)grow destructively, they are also called malignant.

The most common breast cancer, ductal carcinoma, starts in the lactiferous ducts that transport breast milk to the nipple. Another type, lobular carcinoma, starts in the mammary gland lobules that produce milk.

Carcinoma in situ (CIS) is the term used for a small, early cancer that does not involve surrounding tissues. Invasive breast cancer is larger and spreads to lymphatic vessels and lymph nodes under the arm (axillary lymph nodes). The worst form, metastatic cancer, spreads to other parts of the body.

Breast cancer is diagnosed in 1 in 8 women in the United States with most cases occurring in women over age 50. Breast cancer is the second leading cause of cancer death in women, following lung cancer. Rarely, this disease can occur in men.

Causes and Risk Factors

Female hormones, estrogen and progesterone, stimulate the growth of breast cancer. Many of the identified risk factors for breast cancer are related to a person’s exposure to mammary gland lobules (in cross-section view of breast)these hormones.

Risk Factors for Breast Cancer

  • Female gender
  • Older age
  • Family history of breast cancer
  • Personal history of breast cancer
  • Early onset of menstruation (before age 12) or late menopause (after age 55)
  • Chest radiation
  • Women without children or first birth after age 30
  • Ongoing use of oral contraceptives
  • Hormone replacement therapy for menopause
  • Sedentary lifestyle
  • Alcohol
  • Obesity after menopause

Some breast cancers are linked to inherited defects (mutations) in certain genes. BRCA1 and BRCA2 are two genes associated with hereditary breast and ovarian cancer. DNA health testing can help you determine if you are at genetically higher risk of breast cancer due to BRCA1 and BRCA2.

A female’s age at menarche (first period), age at menopause, and reproductive history are important because women with a greater number of menstrual cycles over their lifetime have a higher exposure to estrogen.


The typical symptoms of breast cancer include:

  • A breast lump
  • Swelling or redness of the breast
  • Dimpling of the skin
  • Pitting of the skin (like an orange)
  • Inversion of the nipple
  • Redness, scaliness or thickened of the nipple
  • Nipple discharge
  • Enlarged lymph nodes under the arm or near the collarbone.

Diagnosis and Treatment

Cross-section of breast

The diagnosis of breast cancer is based on the patient’s symptoms, physical exam, and test results.

Evaluation for Breast Cancer

  • Breast examination
  • Mammogram (an x-ray of the breast)
  • Ultrasound (the use of sound waves to produce an image of the breast)
  • Breast biopsy (a sample of tissue is removed and examined for cancer cells)
  • Magnetic resonance imaging or MRI

Stages of Breast Cancer

When breast cancer is diagnosed, the physician first determines the extent (stage) of the disease. The stage (based on the status of the lymph nodes, tumor size, and any spread to distant sites) determines the course of treatment and likelihood of survival.

  • Stage 0, the earliest breast cancer, is termed carcinoma in situ (CIS). This small, noninvasive cancer has not spread to any lymph nodes and is usually curable.
  • Stage I is a small tumor without spread to the lymph nodes or a tiny amount of cancer is detected in nearby lymph nodes.
  • Stage II is a larger tumor and/or involves a few nearby lymph nodes.
  • Stage III is a very large tumor; or the cancer has spread to the skin over the breast or muscle beneath the breast; or the cancer involves many nearby lymph nodes. The survival rate is significantly reduced for stage III breast cancer.
  • Stage IV is a tumor that has metastasized (spread to distant locations). Breast cancer commonly spreads to bone, liver, lung, or brain. Statistically with stage IV breast cancer there is only a 22 percent chance of survival beyond five years, underscoring the importance of early detection of breast cancer.
axillary nodes and nearby lymphatic vessels

For staging purposes, a computed tomography is performed to provide detailed images of the breast. A bone scan is obtained to check for spread of cancer to the bones. Positron emission tomography (PET) scan also detects the spread of cancer. The status of the lymph nodes is determined when biopsies are performed during surgery.

Treatment with Surgery

  • Lumpectomy, for early-stage tumors, involves excising the tumor but not removing the entire breast.
  • Mastectomy, for large tumors, removes all of the breast tissue.
  • Sentinel node biopsy checks for cancer in the most dominant axillary lymph node. If cancer is not detected in the sentinel lymph node, it is unlikely to have spread to any other nodes.
  • Axillary lymph node dissection is a more extensive removal of lymph nodes that is required when cancer is present in the sentinel lymph node.
  • Double mastectomy (removal of both breasts) is a preventive option for patients at a high risk of developing cancer in the other breast.
  • In some cases, breast reconstruction with artificial implants is performed.

Radiation Therapy

Following lumpectomy, the chest is often treated with radiation to destroy remaining cancer cells and prevent a recurrence of cancer. Radiation is sometimes used after mastectomy as well.


Chemotherapy is prescribed when cancer involves the lymph nodes. These medications may be administered after surgery to destroy unseen cancer cells remaining in the body. Sometimes chemotherapy is given before surgery to shrink large tumors and facilitate their removal with surgery.

Hormone Therapy

Most breast cancers are hormone receptor positive (carrying receptors for estrogen and progesterone). Certain drugs, selective estrogen receptor modulator (SERM) medications, block the action of estrogen and inhibit breast cancer growth. Other medications work by lowering estrogen levels in the body.

Targeted Drugs

Some breast cancers produce large amounts of a protein called human growth factor receptor 2 (HER2). Several medications are designed to target these types of cancers.

Alternative Treatments

Exercise and activities like yoga or tai chi are often recommended to reduce stress.


There is a lower incidence of breast cancer in countries where the diet is low in fat; therefore, a low-fat diet and normal body weight may be preventative. Additionally, avoidance or limited use of alcohol lowers the risk for this disease.

Studies show that moderate to vigorous exercise significantly lowers the risk of breast cancer. There is still debate over how much exercise is needed.

Genetic testing for mutations in BRCA1 and BRCA2 genes is an option for women with multiple family members with breast or ovarian cancer. Women at very high risk may receive prophylactic medications or opt for prophylactic double mastectomy to reduce their risk of developing breast cancer.


To detect cancer before there are any symptoms, screening consists of a triad of breast self-examination, clinical breast examination by a health care professional, and screening mammography. Physicians recommend that women 20 years and older perform monthly breast self-examinations. Women in their 20s and 30s should receive a clinical breast examination by a health care professional at least every three years. Over age 40, women should receive a clinical breast examination every year. For women age 40 and older, an annual screening mammogram is recommended.


  • Davidson N. Chapter 204. Breast Cancer and Benign Breast Disorders. Goldman L, Schafer AI, eds. Goldman’s Cecil Medicine, 24e. Philadelphia, PA: Elsevier Saunders; 2012.
  • Breast Cancer Detailed Guide. American Cancer Society website. Accessed May 1, 2014.
  • Breast Cancer. Mayo Clinic website. Accessed May 1, 2014.

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Tina Shahian, PhD

Tina is a writer for Innerbody Research, where she has written a large body of informative guides about health conditions.


A communication specialist in life science and biotech subjects, Tina’s successful career is rooted in her ability to convey complex scientific topics to diverse audiences. Tina earned her PhD in Biochemistry from the University of California, San Francisco and her BS degree in Cell Biology from U.C. Davis. Tina Shahian’s Linkedin profile.


In her spare time, Tina enjoys drawing science-related cartoons.