There are two main types of breast cancer:
- Ductal carcinoma begins in the ducts that carry milk from the breast to the nipple. Most breast cancers are 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, which means that estrogen causes the breast cancer tumor to grow. This type of cancer called cancer positive for estrogen receptor positive cancer or ER. Some women have what is known as breast cancer for HER2 positive. 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) grow faster. Experts think that women with breast cancer have HER2-positive more aggressive disease and increased risk of recurrence than those without this cancer.