Targeted Therapy for Breast Cancer

Why is Targeted Therapy Used for Breast Cancer?

Unlike chemotherapy, targeted therapies only kill cancer cells, leaving healthy cells alone. Instead of targeting the hormone receptors estrogen and progesterone, they target other parts of the cancer cell. This often reduces the amount of side effects a patient may experience. With that said, there are unique side effects with targeted therapy that can be explained by your breast cancer doctor.

Breast cancer can have many different attributes, which means not every breast cancer patient is a good fit for the available targeted therapies. Additionally, The American Society of Clinical Oncology (ASCO) states that studies show that not all tumors have the same targets, therefore, the same targeted treatment does not work for everyone. If targeted therapies are administered, however, they may be given in addition to another form of cancer treatment such as chemotherapy, radiation therapy, or hormone therapy.

Types of Targeted Therapy Used for Breast Cancer

There are two main types of targeted therapy:

1. Monoclonal antibodies - which block a specific target on the outside of cancer cells
2. Small-molecule drugs - which can block the process that helps cancer cells multiply and spread.

Drugs used in targeted therapy have been developed to target specific cell changes. Therefore, the drugs given to patients are usually based on their specific hormone status and the type of breast cancer. Below is an explanation of the various types of targeted therapies that an oncologist may choose to use if one has been identified as a good fit for the type of breast cancer.

Targeted Therapy for HER2-Positive Breast Cancer

Cancers known as HER2-positive breast cancers typically grow and spread more aggressively. A variety of drugs have been developed that target this type of breast cancer, including:

• Nerlynx: Nerlynx (chemical name: neratinib) is an irreversible pan-HER inhibitor. Nerlynx works against HER2-positive breast cancer by blocking the cancer cells’ ability to receive growth signals.
• Herceptin: Herceptin (chemical name: trastuzumab) works against HER2-positive breast cancers by blocking the ability of the cancer cells to receive chemical signals that tell the cells to grow.
• Perjeta: Like Herceptin, Perjeta (chemical name: pertuzumab) works against HER2-positive breast cancers by blocking the cancer cells’ ability to receive growth signals.
• Kadcyla: Kadcyla (chemical name: T-DM1 or ado-trastuzumab emtansine) is a combination of Herceptin and the chemotherapy medicine emtansine. Kadcyla was designed to deliver emtansine to cancer cells in a targeted way by attaching emtansine to Herceptin. Herceptin then carries emtansine to the HER2-positive cancer cells.
• Tykerb: Tykerb (chemical name: lapatinib) works against HER2-positive breast cancers by blocking certain proteins that can cause uncontrolled cell growth.

Targeted Therapy for Hormone Receptor-Positive Breast Cancer

For women with hormone receptor-positive cancers, treatment often begins with hormone therapy. Certain targeted therapy drugs have been developed to help make hormone therapy even more effective, including:

• Afinitor: Afinitor (chemical name: everolimus) is a mTOR (mammalian target of rapamycin) inhibitor. Afinitor works against hormone-receptor-positive breast cancers that have stopped responding to Arimidex or Femara by stopping the cancer cells from getting the energy they need.
• Avastin: Avastin (chemical name: bevacizumab) works by blocking the growth of new blood vessels that cancer cells depend on to grow and function.
• Ibrance: Ibrance (chemical name: palbociclib) is a cyclin-dependent kinase 4/6 inhibitor. A kinase is a type of protein in the body that helps control cell division. Ibrance works by stopping cancer cells from dividing and growing.
• Kisqali: Kisqali (chemical name: ribociclib, formerly called LEE011) is also a cyclin-dependent kinase 4/6 inhibitor like Ibrance. A kinase is a type of protein in the body that helps control cell division. Kisqali works by stopping cancer cells from dividing and growing.
• Verzenio: Verzenio (chemical name: abemaciclib) is cyclin-dependent kinase 4/6 inhibitor, like Ibrance and Kisqali. A kinase is a type of protein in the body that helps control cell division. Verzenio works by stopping cancer cells from dividing and growing.

Targeted Therapy for Women with BRCA Gene Mutations

Hereditary breast cancer syndrome is caused by inherited gene changes in BRCA1 and BRCA2 and is targeted with a type of drug known as a PARP inhibitor:

• Lynparza: Lynparza (chemical name: olaparib) is a PARP inhibitor. The PARP enzyme fixes DNA damage in both healthy and cancer cells. Lynparza works against metastatic HER2-negative breast cancer with a BRCA1 or BRCA2 mutation by making it very difficult for these cancer cells to fix DNA damage.

Side Effects of Targeted Therapy in Breast Cancer Treatment

Not everyone who undergoes targeted therapy for breast cancer will experience side effects. Additionally, the severity of side effects can vary based on the individual as well as the drugs used.

For those who do experience side effects, most will go away over time after treatment ends and the healthy cells recover. Again, the time it takes to get past the side effects varies from person to person. At this time, the duration of side effects is unknown.

Some common side effects that patients may experience from targeted breast therapy may include:

• High blood pressure
• Bleeding or clotting problems
• Slow wound healing
• Heart damage
• Autoimmune reactions
• Swelling (especially around the eyes)

Some patients may also experience skin problems due to targeted therapy treatment. Skin problems may include:

• Rash or skin changes that develop slowly over days to weeks. This can include becoming sensitive to the sun (photosensitivity), itching, dry skin, hand-foot syndrome, and red, sore cuticles.
• Changes in hair growth, such as hair that has become thin, dry, brittle, or even curly. Some people may experience bald patches or complete loss of scalp hair due to long-term use of targeted therapy drugs. For most men and women, facial hair may grow faster than usual. Some facial hair growth in men, however, may slow down.
• Changes in hair or skin color, that may include skin or hair turning a yellowish color during treatment. For some, hair or skin may get darker.
• Changes in and around the eyes, which can include burning, dryness, and redness. Eyelids may become red, tender, and swollen. Lashes may also become crusty.

Other side effects of targeted therapy that mimic standard chemotherapy side effects can include:

• Nausea and vomiting
• Diarrhea or constipation
• Mouth sores
• A cough
• Shortness of breath
• Fatigue
• Headaches
• Hair loss