Molecular Subtypes of Breast Cancer

Molecular subtyping is a system for grouping breast cancer tumors that have similar genetic makeup into categories of cancers that behave in similar manners. This can lead to better treatments and outcomes for patients with breast cancer.

Some subtypes are based on whether or not a breast cancer cell has a receptor — a protein that attaches to estrogen and/or progesterone. Estrogen and progesterone are the hormones that fuel cancer growth. Breast cancer can contain receptors for one of these hormones, both of them or neither of them.

These subtypes are:

• Estrogen Receptive Positive: Breast cancer with receptors for estrogen is called ER positive.
   
• Estrogen Receptive Negative: Breast cancer with no receptors for estrogen is called ER negative.
   
• Progesterone Receptive Positive: Breast cancer with receptors for progesterone is called PR positive.
   
• Progesterone Receptive Negative: Breast cancer with no receptors for progesterone is called PR negative.
   
• HER2-Positive Breast Cancer: HER2 is an abbreviation for a protein called “human epidermal growth factor receptor 2.” HER2 promotes the uncontrolled growth of cancer cells. If a patient has HER2-positive breast cancer, it means the cancer cells are making an excess of the HER2 protein. HER2-positive breast cancer is an aggressive disease.
   
• Triple-Negative Breast Cancer: Some breast cancers lack receptors for estrogen, progesterone and HER2. These are called triple negative breast cancer, and affect about 10 to 15 percent of breast cancers. Women with triple-negative breast cancers tend to have genetic mutations more often than other women. Mutations of the BRCA1 and BRCA2 genes are examples of this. The mutations make treating the breast cancer more challenging.