Did you know that there are many different types of breast cancer? The term breast cancer is used to describe any tumour that is associated with the breast tissue. The general medical term for most tumours of the breast is an adenocarcinoma.

Breast cancer is often described by where it begins to grow in the breast: usually in either the milk ducts in the breast (ductal carcinoma) or the milk-producing lobules (lobular carcinoma). The pathologist can tell the difference by looking through a microscope at a slice of the tumor removed by the surgeon. If the tumor is caught early enough to still be in the ducts or lobules, it is called in situ. If it has spread outside of those structures, it is called infiltrating or invasive. For example, the most common type of malignant breast cancer, which starts in the milk ducts and spreads to tissues outside of the duct, is called invasive ductal carcinoma.

The main types of breast cancer are:

  • ductal carcinoma in situ (DCIS)
  • lobular carcinoma in situ (LCIS)
  • invasive (infiltrating) ductal carcinoma (IDC)
  • invasive (infiltrating) lobular carcinoma (ILC)
  • inflammatory breast cancer

You may also hear other descriptions:

  • Triple negative breast cancer: This is any type of breast cancer where the tumour is not sensitive to estrogen or progesterone hormones and contains low levels of the protein HER2/neu.
  • Estrogen sensitive: Estrogen triggers the growth of the tumour. Most breast cancers (about 66%) are estrogen sensitive or "estrogen positive." This means that they will respond to hormonal therapy with medications such as tamoxifen.
  • Paget's disease of the breast: This is a rare form of breast cancer that spreads to the nipple.

The factors such as type of breast cancer and the unique characteristics of the tumour help to define what treatment options are available.

Ruth Ackerman