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The Voice of People With Breast Cancer


Treatments & Side Effects

Systemic Therapy

Systemic therapies, unlike the localized therapies, surgery and radiation, are delivered to the entire body. Like radiation, they can be used as primary therapy (often in stage IV disease), or can be used in addition to the primary therapy of surgery. This can be done before surgery (“neoadjuvant”), or after surgery (“adjuvant”).  Studies show that neoadjuvant and adjuvant treatments are equally effective at preventing breast cancer from recurring. Your physician may recommend neoadjuvant treatment in the case of a large tumour, or lymph node involvement, to help achieve a successful surgery. The current systemic therapies for breast cancer include chemotherapy, hormonal therapy and targeted therapies. 


Chemotherapy uses medications to damage and destroy cancer cells. In early stage breast cancer, chemotherapy may be given after surgery to eliminate any remaining cancer cells and reduce the risk of recurrence; sometimes chemotherapy may be given before surgery to shrink the tumour to an operable size.  In metastatic breast cancer, chemotherapy is given to shrink or slow the growth of tumours or to ease symptoms of the cancer itself. Many breast cancer patients respond well to chemotherapy.  There are many different chemotherapy drugs and drug combinations.  You and your doctor will make decisions about chemotherapy based on the type of cancer and factors in the pathology report.

Endocrine therapy 

Estrogen and progesterone can stimulate the growth of HR+ breast cancers, so hormonal therapy is used to block their action. These therapies are used to:

  • block estrogen or progesterone receptors on the breast cancer cells, or
  • reduce the number of receptors, or
  • block the ovaries from producing hormones, or
  • block the actions of an enzyme, aromatase, which in turn lowers the level of estrogen in the body.

The choice of hormonal therapy for breast cancer and the length of time it is given depends on many factors, including whether menopause has been reached, the stage of breast cancer, other health problems (such as osteoporosis or blood clot risk factors) that may prevent taking certain types of hormonal therapy, other hormonal therapies previously taken, and disease progression.

Targeted therapy 

Targeted therapies target certain parts of cancer cells that make them different from other cells in order to selectively kill or stop them from growing. In general, they work to:

  • Stop the growth and division of cancer cells by blocking the signaling pathways that tell them to grow
  • Alter the proteins of the cancer cells so they will die; prevent new blood vessels from feeding the cancer cells
  • Stimulate the immune system to attack the cancer cells
  • Destroy the cancer cells by carrying a toxin to only to them.
Support Medications

Support medications are drugs given to counteract the side effects of your cancer or its treatment. Please refer to our side effects section to learn more about treatment side effects and possible treatments to manage them.

Understanding Biologics and Biosimilars 

Some medications to treat breast cancer, like Herceptin (trastuzumab) and Perjeta (pertuzumab), are called biologics. Biologics are medications that are made from living cells, like animal cells, bacteria or yeast. Because biologic drugs are made from living cells and are often large complex molecules, every batch that is made is highly similar but not identical.

Biosimilars are drugs that are made to be highly similar to the reference biologic drug (the original brand name biologic drug); however, it isn’t the exact replica because of the complexity of the molecule.

Biosimilars are approved and monitored by Health Canada to ensure that they are safe and work just as well as the reference biologic. If you are prescribed a biosimilar drug, you should expect to have the same results and the same side effects as the reference biologic.

There are currently several biosimilars for trastuzumab (Herceptin) that are approved by Health Canada and that are being used in provinces across Canada.

To learn more about biosimilars download this factsheet or click here.

What to do if drugs aren’t covered

See the Living with Breast Cancer or Living with Metastatic Breast Cancer sections of this website for details.

Systemic therapies play an important role in the treatment of breast cancer.  It’s important that you understand the risks and benefits of these valuable treatments.  If you’re uncertain, be sure to ask your healthcare team for information.



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