Breast cancer is not just one disease. There are many different types of breast cancer.
Breast cancer can be classified by where it originates in the breast:
- Ductal carcinoma in situ (DCIS): This type of breast cancer results an uncontrolled growth of cells within the lining of a milk duct. It is sometimes referred to as pre-cancerous because it has not spread outside the duct into surrounding breast tissue. It rarely will form a tumor so it will usually only be detected from a screening mammogram.
- Invasive Ductal Carcinoma (IDC): This is breast cancer that began in the milk ducts but has spread to surrounding breast tissue.
- Invasive Lobular Carcinoma (ILC): This is breast cancer that began in the lobules of the breast but has spread to surrounding breast tissue.
Breast cancer can also be sub-categorized by certain characteristics that the cancer cells may have:
- Estrogen-positive (ER+) breast cancer is sensitive to the hormone estrogen. ER+ cancer cells have receptors for estrogen. When estrogen attaches to these receptors, cancer cells are stimulated to grow and divide.
- Progesterone-positive (PR+) breast cancer is sensitive to the hormone progesterone. PR+ cancer cells that have receptors for progesterone.
- HER2-positive breast cancer has cancer cells that make too much of a protein called HER2. HER2 proteins are found on the surface of cancer cells and can receive signals from outside the cell that stimulate the cells to grow and divide.
- Triple negative breast cancer is characterized by cancer cells that lack both estrogen and progesterone receptors and do not have an excess of HER2 protein.
There are also some less common types of breast cancer, which include:
- Inflammatory breast cancer: cancer cells block the lymph vessels in the skin, causing the breast to look reddish and feel warm
- Paget’s disease: tumor is close to the nipple and causes scaling and inflammation of the nipple; there is usually an underlying in situ or invasive ductal cancer in the breast
- Phyllodes tumors: tumor that grows in the connective tissue of the breast
- Metaplastic breast cancer: cancer begins in one type of cell and changes into another type of cell
- Medullary breast cancer: rare subtype of invasive ductal cancer; tumor has a similar colour and shape as the part of the brain called the medulla.