Types of breast cancer
What kind of breast cancer do you have?
Understanding the type or classification of your breast cancer is essential to determining your treatment options.
Breast cancer exists in many different forms. The more we know about each type of breast cancer, the easier it is to treat individual patients. There are different ways to classify types of breast cancer. As we learn more about breast cancer, new classification systems have emerged and continue to emerge. The earliest classification of types of breast cancer is based on how the cancer looks under the microscope. There is increasing interest in the genetic or molecular features of the cancer, which may be even more important than how a breast cancer looks. These features give some indication about which treatments the cancer will respond to and include whether the cancer is hormone sensitive (estrogen or progesterone) or if it has too much of a known gene as HER2. In the near future, many more genetic features may be part of the standard diagnosis of breast cancer and may be more important than our current classification.
The newest research suggests there are 4 basic types of breast cancers:
Luminal A and luminal B types: The luminal types are estrogen receptor (ER)–positive, usually low grade, and tend to grow fairly slowly. The gene expression patterns of these cancers are similar to normal cells that line the breast ducts and glands (the lining of a duct or gland is called its lumen). Luminal A cancers have the best prognosis. Luminal B cancers generally grow somewhat faster than the luminal A cancers and their prognosis is not quite as good.
HER2 type: These cancers have extra copies of the HER2 gene and several other genes. They usually have a high-grade appearance under the microscope. These cancers tend to grow more quickly and have a worse prognosis, although they often can be treated successfully with targeted therapies such as trastuzumab (Herceptin) and lapatinib (Tykerb).
Basal type: Most of these cancers are of the so-called triple-negative type, that is, they lack estrogen or progesterone receptors and have normal amounts of HER2. The gene expression patterns of these cancers are similar to cells in the deeper basal layers of breast ducts and glands. This type is more common among women with BRCA1 gene mutations. For reasons that are not well understood, this cancer is also more common among younger and African-American women. These are high-grade cancers that tend to grow quickly and have a poor prognosis. Hormone therapy and anti-HER2 therapies like trastuzumab and lapatinib are not effective against these cancers, although chemotherapy can be helpful. A great deal of research is being done to find better ways to treat these cancers.
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