Types of Breast cancer

Breast cancer is commonly divided according to its invasive status and whether it has certain receptors or not. It is important to know the different types of breast cancer because treatment (and prognosis) can vary significantly among its different subtypes.

Types of Breast cancer per invasion status:

Breast cancer can be divided into two major groups based on their invasion status: invasive and non-invasive.

Non-invasive Breast cancer (sometimes called “carcinoma-in-situ”)

Non-invasive breast cancer means that there are cancer cells in the breast but they are not invading the surrounding tissue. Surgery is the main treatment for non-invasive breast cancer but radiotherapy (or even endocrine therapy) may be offered sometimes to patients after surgery if the risk of recurrence is high. There are two types of non-invasive breast cancer:

  • Ductal carcinoma in situ (DCIS): 

This is the earliest form of breast cancer. It happens when there are cancer cells in the ducts of the breast, but these cells are contained (in situ) and have not spread into surrounding normal breast tissue.

  • Lobular carcinoma in situ (LCIS):

This is not breast cancer but when present indicates that a woman has an increased risk of developing breast cancer later in life. It is important to know that most women with LCIS do not get breast cancer.

Invasive breast cancer

This means the cancer cells have spread outside the lining of the ducts or lobes into the surrounding breast tissue.

  • Invasive ductal breast cancer

This means that cancer started within the breast milk ducts. Most invasive breast cancers (80%) start in the ducts of the breast.

  • Invasive lobular breast cancer

About 1 in 10 invasive breast cancers (10%) start in the lobes of the breast. This subtype is usually difficult to see on a mammogram. Radiologists may prefer to do breast MRI to fully assess the extent of this cancer within the breast tissue.

Type of Breast cancer per receptor status:

Receptors are proteins that exist on the surfaces of all cells (normal and malignant) to connect them with the rest of the body. Certain receptors receive certain signals asking cells to do certain jobs. In cancer, some receptors may start encouraging cells to grow and divide continuously even without receiving signals from the outside.

In breast cancer, there are three receptors that may (or may not) exist on the cell surface:

  1. Oestrogen receptors
  2. Progesterone receptors
  3. HER-2 receptors

Some facts about receptors:

  • When oncologists say that a certain receptor is positive, they mean that this receptor is present in cancer cells.  Conversely, when they say that it is negative, they mean that it is absent.
  • Doctors usually call oestrogen receptors: ER-receptors, and call progesterone receptors: PR-receptors.
  • When either ER or PR receptors are positive (present), oncologists can use endocrine therapy to fight cancer. Their presence is usually a good sign (good prognostic factor).
  • ER and/or PR receptors are usually present in about 70% of all breast cancers.
  • HER2 receptors are positive in about 20% of all breast cancers.
  • When HER2 receptors are positive, oncologists will use a group of targeted therapy called: anti-HER2 drugs to fight cancer. This may include Trastuzumab (Also called Herceptin), Pertuzumab (or Perjeta) and Trastuzumab Emtansine (also called Kadsyla).
  • When three receptors are absent, doctors will call this subtype of cancer: Triple-negative breast cancer.
  • Triple-negative breast cancer constitute about 10% of all breast cancers (1 out 10 patients)

Invasion status and receptors status are two common ways to divide breast cancer into different subtypes. There are other ways to do this but they are beyond the scope of this article. You can ask your oncologists for more information.