What is breast cancer?

Cells in the body normally divide (reproduce) only when new cells are needed. Sometimes, cells in a part of the body grow and divide out of control, which creates a mass of tissue called a tumor. If the cells that are growing out of control are normal cells, the tumor is called benign (not cancerous). If, however, the cells that are growing out of control are abnormal and don't function like the body's normal cells, the tumor is called malignant (cancerous).

Cancers are named after the part of the body from which they originate. Breast cancer originates in the breast tissue. Like other cancers, breast cancer can invade and grow into the tissue surrounding the breast. It can also travel to other parts of the body and form new tumors, a process called metastasis.

Who gets breast cancer?

Breast cancer is the most common cancer among women other than skin cancer. Increasing age is the most common risk factor for developing breast cancer, with 66 perccent of breast cancer patients being diagnosed after the age of 55.

In the US, breast cancer is the second-leading cause of cancer death in women after lung cancer, and it's the leading cause of cancer death among women ages 35 to 54. Only 5 to 10 percent of breast cancers occur in women with a clearly defined genetic predisposition for the disease. The majority of breast cancer cases are "sporadic”, meaning there is no definitive gene mutation.

Does a benign breast condition mean that I have a higher risk of getting breast cancer?

Benign breast conditions rarely increase your risk of breast cancer. Some women have biopsies that show a condition called hyperplasia (excessive cell growth). This condition increases your risk only slightly.

When the biopsy shows hyperplasia and abnormal cells, which is a condition called atypical hyperplasia, your risk of breast cancer increases somewhat more. Atypical hyperplasia occurs in about 5 percent of benign breast biopsies.

What are the types of breast cancer?

The most common types of breast cancer are:

  • Infiltrating (invasive) ductal carcinoma. This cancer starts in the milk ducts of the breast. It then breaks through the wall of the duct and invades the surrounding tissue in the breast. This is the most common form of breast cancer, accounting for 80 percent of cases.
  • Ductal carcinoma in situ is ductal carcinoma in its earliest stage, or precancerous (stage 0). In situ refers to the fact that the cancer hasn't spread beyond its point of origin. In this case, the disease is confined to the milk ducts and has not invaded nearby breast tissue. If untreated, ductal carcinoma in situ may become invasive cancer. It is almost always curable.
  • Infiltrating (invasive) lobular carcinoma. This cancer begins in the lobules of the breast where breast milk is produced, but has spread to surrounding tissues in the breast. It accounts for 10 to 15 percent of breast cancers. This cancer can be more difficult to diagnose with mammograms.
  • Lobular carcinoma in situ is a marker for cancer that is only in the lobules of the breast. It isn't a true cancer, but serves as a marker for the increased risk of developing breast cancer later, possibly in both or either breasts. Thus, it is important for women with lobular carcinoma in situ to have regular clinical breast exams and mammograms.

Cancers can also form in other parts of the breast but are less common. These include:

  • Angiosarcomas. This type of cancer begins in the cells that make up the lining of blood or lymph vessels. These cancers can start in breast tissue or breast skin. They are rare.
  • Inflammatory breast cancer. This type of cancer is rare and different from other types of breast cancer. It is caused by obstructive cancer cells in the skin’s lymph vessels.
  • Paget disease of the breast, also known as Paget disease of the nipple. This cancer affects the skin of the nipple and areola (the skin around the nipple.)
  • Phyllodes tumors. These are rare, and most of these masses are not cancer. However, some are cancerous. These tumors begin in the breast’s connective tissue, which is called the stroma.

What are the stages of breast cancer?

There are two different staging systems for breast cancer. One is called “anatomic staging” while the other is “prognostic staging”. The anatomic staging is defined by the areas of the body where the breast cancer is found and helps to define appropriate treatment. The prognostic staging helps medical professionals communicate how likely a patient is to be cured of the cancer assuming that all appropriate treatment is given.

The anatomic staging system is as follows:

Stage 0 breast disease is when the disease is localized to the milk ducts (ductal carcinoma in situ).

Stage I breast cancer: The cancer is smaller than 2-inches across and hasn't spread anywhere, including no involvement in the lymph nodes.

Stage II breast cancer is one of the following:

  • The tumor is less than 2 cm across but has spread to the underarm lymph nodes (IIA)
  • The tumor is between 2 and 5 cm (with or without spread to the lymph nodes)
  • The tumor is larger than 5 cm and has not spread to the lymph nodes under the arm (both IIB)

Stage III breast cancer is also called "locally advanced breast cancer." The tumor is any size with cancerous lymph nodes that adhere to one another or to surrounding tissue (IIIA). Stage IIIB breast cancer is a tumor of any size that has spread to the skin, chest wall, or internal mammary lymph nodes (located beneath the breast and inside the chest).

Stage IV breast cancer is defined as a tumor, regardless of size, that has spread to areas away from the breast, such as bones, lungs, liver or brain.

What causes breast cancer?

We do not know what causes breast cancer, although we do know that certain risk factors may put you at higher risk of developing it. A woman's age, genetic factors, family history, personal health history, and diet all contribute to breast cancer risk.

What are the risk factors for breast cancer?

Like many conditions, risk factors for breast cancer fall into the categories of things you can control and things that you cannot control. Risk factors affect your chances of getting a disease, but having a risk factor does not mean that you are guaranteed to get a certain disease.

Controllable risk factors for breast cancer

  • Alcohol consumption. The risk of breast cancer increases with the amount of alcohol consumed. For instance, women who consume 2 or 3 alcoholic beverages daily have an approximately 20 percent higher risk of getting breast cancer than women who do not drink at all.
  • Body weight. Being obese is a risk factor for breast cancer. It is important to eat a healthy diet and exercise regularly.
  • Breast implants. Having silicone breast implants and resulting scar tissue make it harder to distinguish problems on regular mammograms. It is best to have a few more images (called implant displacement views) to improve the examination. There is also a rare cancer called anaplastic large cell lymphoma (ALCL) that is associated with the implants.
  • Choosing not to breastfeed. Not breastfeeding can raise the risk.
  • Using hormone-based prescriptions. This includes using hormone replacement therapy during menopause for more than 5 years and taking certain types of birth control pills.

Non-controllable risk factors for breast cancer

  • Being a woman. Although men do get breast cancer, it is far more common in women.
  • Breast density. You are at higher risk of breast cancer if you have dense breasts. It can also make it harder to see tumors during mammograms.
  • Getting older. Aging is a factor. A majority of new breast cancer diagnoses come after the age of 55.
  • Reproductive factors. These include getting your period before age 12, entering menopause after age 55, having no children, or having your first child after 30.
  • Exposure to radiation. This type of exposure could result from having many fluoroscopy X-rays or from being treated with radiation to the chest area.
  • Having a family history of breast cancer, or having genetic mutations related to certain types of breast cancer. Family history that includes having a first degree relative (mother, sister, daughter, father, brother, son) with breast cancer poses a higher risk for you. If you have more than one relative on either side of your family with breast cancer, you have a higher risk. In terms of genetic mutations, these include changes to genes like BRCA1 and BRCA2.
  • Having already had breast cancer. The risk is higher for you if you have already had breast cancer and/or certain types of benign breast conditions such as lobular carcinoma in situ, ductal carcinoma in situ, or atypical hyperplasia.
  • Exposure to diethylstilbestrol (DES). DES was prescribed to some pregnant women in the United States during 1940-1971. If you took DES, or your mother took DES, you have a higher risk of breast cancer.

What are the warning signs of breast cancer?

  • A lump or thickening in or near the breast or in the underarm that persists through the menstrual cycle
  • A mass or lump, which may feel as small as a pea
  • A change in the size, shape, or contour of the breast
  • A blood-stained or clear fluid discharge from the nipple
  • A change in the look or feel of the skin on the breast or nipple (dimpled, puckered, scaly, or inflamed)
  • Redness of the skin on the breast or nipple
  • An area that is distinctly different from any other area on either breast
  • A marble-like hardened area under the skin

These changes may be found when performing monthly breast self-exams. By performing breast self-exams, you can become familiar with the normal monthly changes in your breasts.

Breast self-examination should be performed at the same time each month, three to five days after your menstrual period ends. If you have stopped menstruating, perform the exam on the same day of each month.

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