When you get a breast cancer diagnosis, you’ll be told what type of cancer you have. Your doctor gets a good idea of how the tumor may act and what kind of treatments may work best by knowing the type.
You may be told your cancer is:
- Endocrine receptor-positive (estrogen or progesterone receptors)
- Triple positive: positive for estrogen receptors, progesterone receptors, and HER2
- Triple negative: not positive for estrogen receptors, progesterone receptors, and HER2
For all of these, surgery and radiation are possible treatments, but ones that involve medications -- such as chemotherapy, hormone therapies, and targeted therapies -- are different. They are specific to the type of cancer.
Hormone Receptor-Positive Breast Cancer
About 80% of all breast cancers are “ER-positive.” That means the cancer cells grow in response to the hormone estrogen. About 65% of these are also “PR-positive.” They grow in response to another hormone, progesterone.
If your breast cancer has a significant number of receptors for either estrogen or progesterone, it’s considered hormone-receptor positive.
Tumors that are ER/PR-positive are much more likely to respond to hormone therapy than tumors that are ER/PR-negative.
You may have hormone therapy after surgery, chemotherapy, and radiation are finished. These treatments can help prevent a return of the disease by blocking the effects of estrogen. They do this in one of several ways.
- The medication tamoxifen (Nolvadex) helps stop cancer from coming back by blocking hormone receptors, preventing hormones from binding to them. It’s sometimes taken for up to 5 years after initial treatment for breast cancer.
- A class of medicines called aromatase inhibitors actually stops estrogen production. These include anastrozole (Arimidex), exemestane (Aromasin), and letrozole (Femara). They’re only used in women who’ve already gone through menopause.
HER2-Positive Breast Cancer
In about 20% of breast cancers, the cells make too much of a protein known as HER2. These cancers tend to be aggressive and fast-growing.
For women with HER2-positive breast cancers, the drug trastuzumab (Herceptin) has been shown to dramatically reduce the risk of the cancer coming back. It‘s standard treatment to give this medication along with chemotherapy after surgery to people with breast cancer that’s spread to other areas. It can also be used for early-stage breast cancer. Trastuzumab has far fewer immediate side effects than chemotherapy -- for example, there is usually no nausea or hair loss. But there is a small but real risk of heart damage and possible lung damage. Scientists are still studying how long women should take this medication for the greatest benefit.
- Another drug, lapatinib (Tykerb), is often given if trastuzumab doesn’t help. Ado-trastuzumab emtansine (Kadcyla) can be given after trastuzumab and a class of chemotherapy drugs called taxanes, which are commonly used to treat breast cancer.
- Pertuzumab (Perjeta) can be used with trastuzumab and other chemotherapy medicines to treat advanced breast cancer. This combination can also be given before surgery to treat early breast cancer. In one study, the combination of the two drugs it was shown to extend life.
Triple-Negative Breast Cancer
Some breast cancers -- between 10% and 20% -- are known as “triple negative” because they don’t have estrogen and progesterone receptors and don’t overexpress the HER2 protein. Most breast cancers associated with the gene BRCA1 are triple negative.
These cancers generally respond well to chemotherapy given after surgery. But the cancer tends to come back. So far, no targeted therapies have been developed to help prevent cancer returning in women with triple-negative breast cancer. Cancer experts are studying several promising strategies aimed at triple-negative breast cancer.