Cancers are identified by where they originated. In the case of breast cancer, most originate in the ducts or the lobules of the breast. Common types of breast cancers are:

Non-invasive:


  • Non-invasive breast cancer means that the cancer cells are contained within the milk ducts or lobules. Two types of non-invasive breast cancer are ductal carcinoma in situ (DCIS) and lobular carcinoma in situ (LCIS).

  • DCIS –  cancer is located only in the lining of the milk ducts. It has not spread through the walls of the ducts into the tissue of the breast and cannot spread to lymph nodes or other parts of the body.

  • LCIS – occurs when abnormal cells develop in the lobules and do not spread to other parts of the body. LCIS is not considered to be a true cancer and is not life-threatening, but rather a marker or signal that breast cancer may develop.



Invasive:


  •  Invasive cancer means that the cancer cells have spread beyond the original duct or lobule. The two main types of invasive breast cancer are invasive ductal carcinoma (IDC -sometimes known as infiltrating ductal carcinoma) and invasive lobular carcinoma (ILC).


Breast Cancer Subtype:


Breast cancers can be further classified into different subtypes based on certain characteristics such as their receptor status.



  • Hormone receptors are proteins found in and on breast cells that pick up hormone signals telling the cells to grow. Estrogen and progesterone receptors are found in breast cancer cells that depend on estrogen and related hormones to grow.

  • If breast cancer cells have estrogen receptors, the cancer is called ER-positive breast cancer. If breast cancer cells have progesterone receptors, the cancer is called PR-positive breast cancer. If the cells do not have either of these two receptors, the cancer is called ER/PR-negative.

  • About 80 per cent of breast cancers are ER positive and about two-thirds of breast cancers are both ER and PR positive.


  • HER2-positive breast cancers are breast cancers that test positive for an increased amount of the HER2 protein in the cancer. HER2 proteins are receptors naturally found in every breast cell at varying levels. However, when a breast cell has abnormally high levels of HER2, it can drive breast cancer growth and spread. This overproduction of HER2 occurs when the HER2 gene isn't working properly and causes an overproduction of HER2 receptors (HER2 protein overexpression). This overexpression occurs in about one in five breast cancers. The only way to know if you are overexpressing the HER2 protein is to get tested.

  • Triple negative breast cancers get their name from the fact that they are estrogen receptor negative, progesterone receptor negative and HER2 negative.



Tests that Can Help Reveal the Subtype of Cancer You May (or May Not) Have


After you’ve been diagnosed with breast cancer, there are a few tests that will be done to help doctors figure out if you have specific hormones or proteins that are helping your cancer grow, and help determine the best treatment for your specific type of breast cancer:

  • HER2 status testing is done to find out how much HER2 a tumour makes. This helps your healthcare team plan your treatment.
  • Hormone receptor testing is done at the time of diagnosis for breast cancer or when breast cancer comes back after treatment (recurs).
    • Knowing the hormone receptor status of the tumour helps doctors predict how well hormonal therapy will work and what other treatments may be effective.
    • Hormone receptor status testing is often done at the same time as the HER2 status testing.


Undergoing these tests will tell your heathcare team if hormonal therapy is likely to slow or stop the cancer cells from growing, based on the following results:


  • ER-positive tumours and tumours that are both ER and PR positive are often treated with hormonal therapy.
  • ER-negative PR-positive tumours are sometimes treated with hormonal therapy.
  • Tumours that are both ER-negative and PR-negative (“hormone receptor negative“) are not treated with hormonal therapy.

Hormone receptor status also helps doctors understand a patient’s prognosis and risk of the  breast cancer reccuring after treatment.


Despite the progress achieved with current treatment for HER2-positive early breast cancer, one in four women will eventually see their cancer return.