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Types of Breast Cancer: ER Positive, HER2 Positive, and Triple Negative

One major way of defining your type of breast cancer is whether or not it is:

  • Endocrine receptor (estrogen or progesterone receptor) positive
  • HER2 positive
  • Triple negative, not positive to receptors for estrogen, progesterone, or HER2
  • Triple positive, positive for estrogen receptors, progesterone receptors and HER2

These classifications provide doctors with valuable information about how the tumor acts and what kind of treatments may work best.

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In general, surgical and radiation treatments are similar for these different types of breast cancer. But drug treatments -- such as chemotherapy, endocrine therapies, and other medications -- are usually different. These treatments are targeted to the specific type of cancer.

Hormone Receptor-Positive Breast Cancer

About 75% of all breast cancers are “ER positive.” They 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’s cells have a significant number of receptors for either estrogen or progesterone, your cancer is considered hormone-receptor positive and likely to respond to endocrine therapies.

Breast cancer tumors that are ER/PR-positive are 60% likely to respond to endocrine therapy. Tumors that are ER/PR negative are only 5% to 10% likely to respond to endocrine therapy.

Endocrine therapies for breast cancer are treatments usually taken after surgery, chemotherapy, and/or radiation are finished. They are designed to help prevent recurrence of the disease by blocking the effects of estrogen. They do this in one of several ways.

  • The drug tamoxifen, taken by some women for up to five years after initial treatment for breast cancer, helps prevent recurrence by blocking the estrogen receptors on breast cancer cells and preventing estrogen from binding to them.
  • A class of drugs called aromatase inhibitors actually stops estrogen production in post-menopausal women. These drugs cannot be taken by women who have not yet gone through menopause.

HER2-Positive Breast Cancer

In about 20% to 25% of breast cancers, the cancer cells make too much of a protein known as HER2/neu. These breast cancers tend to be much more aggressive and fast-growing.

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