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Breast cancer

Breast cancer types

There are many different types of breast cancer. To determine an appropriate approach to treating the disease, your doctor will first evaluate the specifics of the breast tumor, including:

  • Whether the disease has spread beyond the breast
  • The type of tissue where the disease began

Most types of breast cancers are adenocarcinomas of the breast. These types of tumors are found in many other common cancers and form in glands or ducts that secrete fluid. Breast adenocarcinomas form in milk-producing glands called lobules or in milk ducts.

Breast cancer occurs in two broad categories: invasive and noninvasive.

Invasive (infiltrating) breast cancer cells break through normal breast tissue barriers and spread to other parts of the body through the bloodstream and lymph nodes.

Noninvasive (in situ) breast cancer cells remain in a particular location of the breast, without spreading to surrounding tissue, lobules or ducts.

Other types of breast cancer include sarcoma of the breast, metaplastic carcinoma, adenocystic carcinoma, phyllodes tumor and angiosarcoma.

Breast cancer is also classified based on where in the breast the disease started (e.g., milk ducts, lobules), how the disease grows and other factors.

Genomic research has also led to a more specific classification of breast cancers, based on their genes and proteins. Sixty percent of breast cancers are estrogen-positive, for example, while 20 percent are HER2-positive, and another 20 percent are triple-negative.

Aggressive breast cancers

Some breast cancers are more aggressive than others. But unlike some other cancers, the type of breast cancer may not always determine how aggressive the disease is in an individual patient.

To determine how aggressive an individual patient’s breast cancer may be, doctors will examine the tumor, look at cancer cells under a microscope and assign a grade from 1 to 3. Grade 3 cancers are considered the most aggressive. Cancers may be considered aggressive when their cells divide quickly, are clearly abnormal compared to other cells and/or have spread or are likely to spread to other parts of the body.

The most aggressive breast cancers include:

Triple-negative breast cancer: This type of breast cancer tests negative for the hormones estrogen and progesterone, and the protein HER2.

Learn more about triple-negative breast cancer

Inflammatory breast cancer: This rare form of cancer is named because it causes breast swelling and redness. 

Learn more about inflammatory breast cancer

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