If you have HER2-positive breast cancer, your oncology team will prescribe a combination of anticancer drugs. This treatment regimen will likely include a few different chemotherapy drugs as well as therapy that specifically targets HER2-positive breast cancers.

Chemotherapy, or chemo, is the use of medicines to kill cancer cells and stop new ones from growing. Cancer cells multiply very quickly, so chemotherapy drugs target cells in the body that grow and divide very quickly.

Other cells in the body, including those in the bone marrow, the lining of the mouth and gut, and the hair follicles, also grow and divide quickly. These cells may also be affected by the chemotherapy drugs and may trigger side effects.

Some chemotherapy drugs can be taken by mouth, but most are given intravenously through an injection into a vein. You will have to go to a clinic or hospital to receive intravenous (IV) chemotherapy medications.

Everyone’s breast cancer is a little bit different. The type of medications your oncology team prescribes will depend on your treatment goals and the characteristics of your particular cancer.

Side effects depend on the types and doses of chemotherapy drugs prescribed by your oncology team. Common chemotherapy side effects include:

  • hair loss
  • nausea and vomiting
  • fatigue or extreme tiredness
  • loss of appetite
  • bleeding or bruising
  • anemia (low red blood cell count)
  • low white blood cell count
  • rash
  • numbness and/or tingling in fingers or toes
  • taste changes

Chemotherapy can destroy red blood cells. These are the cells that help carry oxygen to all the different tissues and organs in your body. If your red blood cell count is low, you might be told that you have anemia. Symptoms of anemia often include:

  • fast heart beat
  • shortness of breath
  • trouble breathing in everyday activities like walking, talking, or climbing stairs
  • dizziness
  • chest pain
  • pale skin, nail beds, mouth, and gums
  • extreme tiredness or fatigue

There are no symptoms of a low white blood cell count, but if you develop an infection you may notice a fever. If you have a fever, alert your oncology team immediately.

When a cancer is HER2-positive, it means that the cancer cells make too much HER2 protein, which can cause tumors to grow more rapidly than with other forms of breast cancer.

Drugs that target the HER2 proteins are the primary treatment for this type of breast cancer, given along with chemotherapy. Your oncology team may refer to these medications as “targeted therapy” or “HER2-directed therapy.”

Trastuzumab (Herceptin) and pertuzumab (Perjeta) are the most commonly used drugs used to treat HER2-positive breast cancer. Neratinib (Nerlynx) is another drug that is sometimes given after trastuzumab.

Some other targeted therapy drugs, such as lapatinib (Tykerb/Tyverb) or ado-trastuzumab emtansine (Kadcyla), are mainly used to treat more advanced HER2-positive breast cancers.

Herceptin and Perjeta are given at the same time as chemotherapy through an IV. HER2-directed therapy is usually given over a longer period of months than chemotherapy.

Herceptin alone is usually continued after chemotherapy has finished, every three weeks for a total of one year.

Side effects for HER2-targeted therapies may include:

  • sleep problems
  • muscle/joint pain
  • redness at the IV site
  • diarrhea
  • nausea
  • tiredness
  • headache
  • mouth sores
  • loss of appetite
  • cold symptoms
  • rash

In general, chemotherapy and HER2-targeted therapies are more likely to be given prior to surgery. You’ll receive these treatments in cycles, with each period of treatment followed by a period of rest to let your body recover.

Chemotherapy begins on the first day of the cycle. Cycles can last anywhere from about two to four weeks, depending on the combination of drugs.

Chemotherapy generally lasts about three to six months. The total length of chemotherapy treatment may vary depending on the stage of breast cancer and a number of other factors.

Herceptin is usually given every three weeks for one year (possibly longer for advanced breast cancer), initially in combination with chemotherapy and then on its own after chemotherapy is complete.

If you have HER2-positive breast cancer, first-line treatment will likely include a targeted drug and chemotherapy. Ask your oncology team any questions you have about targeted therapies, chemotherapy, and your treatment schedule.