Breast cancer is a cancer that starts in the tissues of the breast. There are two main types of breast cancer:
- Ductal carcinoma starts in the tubes (ducts) that move milk from the breast to the nipple. Most breast cancers are of this type.
- Lobular carcinoma starts in parts of the breast, called lobules, that produce milk.
In rare cases, breast cancer can start in other areas of the breast.
Many breast cancers are sensitive to the hormone estrogen. This means that estrogen causes the breast cancer tumor to grow. Such cancer is called estrogen receptor positive cancer or ER positive cancer.
Some women have what's called HER2-positive breast cancer. HER2 refers to a gene that helps cells grow, divide, and repair themselves. When cells have too many copies of this gene, cells—including cancer cells—grow faster. Experts think that women with HER2-positive breast cancer have a more aggressive disease and a higher risk of recurrence than those who do not have this type.
Both estrogen receptor positive breast cancer and HER2-positive breast cancer are generally diagnosed based upon the presence of receptors. Unfortunately, none of these receptors are found in women with triple negative breast cancer. In this diagnosis the cancerous tumor is estrogen receptor-negative, progesterone receptor-negative and HER2-negative, thus giving rise to the name triple negative breast cancer. Depending on the stage of its diagnosis, triple negative breast cancer can be particularly aggressive and more likely to recur than other subtypes of breast cancer. While this type of breast cancer is typically responsive to chemotherapy, because of its triple negative status triple negative tumors generally do not respond to receptor targeted treatments.