How Does Targeted Therapy Treat HER2+ Breast Cancer?

Targeted therapies have made this aggressive subtype highly treatable.

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The field of targeted therapy against cancer started booming in the 1990s, after researchers recognized ways that gene and protein changes affected cancer growth and development. While targeted therapy can’t treat all types of cancers, it can be incredibly effective against certain types.

One type of cancer that has benefited from the emergence of targeted therapy is HER2-positive breast cancer. “While [HER2-positive breast cancer] was classically a more aggressive form of breast cancer, with the targeted therapies we have available now, this is a highly treatable cancer,” says Natalie Berger, MD, hematologist and oncologist at The Mount Sinai Hospital.

What Is HER2-Positive Breast Cancer?

HER2, or HER2/neu, stands for “human epidermal growth factor receptor 2.” It’s a protein that is involved in normal cell growth—but some breast cancer cells may make it in larger numbers than normal, allowing abnormal cells to grow out of control. This is known as HER2-positive breast cancer.

“Because there are so many of these [HER2] proteins expressed, the cell is constantly getting the signal to grow and divide at a very rapid rate,” says Dr. Berger.

Breast cancers that do not have an overexpression of HER2 may instead be fueled by the hormones estrogen or progesterone (hormone receptor-positive breast cancer). A third subtype of breast cancer has nothing to do with HER2 or hormone receptors (triple-negative breast cancer).

Targeted Therapy for HER2-Positive Breast Cancer

A number of different medications have emerged to target HER2 to treat breast cancer.

“What these therapies do is they go directly to this HER2 receptor that's expressed on the cancer cell to stop the signal that's telling these cells to grow and divide,” says Dr. Berger. When this signal is blocked, the cancer cells die.

Because these therapies are more targeted (hence the name) than chemotherapy, they tend to produce fewer and milder side effects. Chemotherapy attacks all rapidly dividing cells, which includes cancer cells but also many normal, healthy cells. (For example, hair cells divide rapidly, leading to chemo-induced hair loss.)

“With targeted treatment for metastatic breast cancer today, patients really can go on continuing to live their life,” says Dr. Berger. “The most important thing in the world is feeling like yourself, and living your life to the fullest.”