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% 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% 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 % 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% 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% 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.

Breast Cancer Stages

What are the stages of breast cancer?

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 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.