Endocrine Therapy

Anti-hormone therapy or endocrine therapy is often used to treat women whose cancers are sensitive to hormones. These cancers are known as estrogen and progesterone receptor-positive cancers. Similar to chemotherapy, this form of therapy can be used to decrease the chance of cancer recurrence. If the cancer has already spread, hormone therapy may shrink and control it. It may also work to prevent new cancers.

Hormonal therapies take advantage of the fact that some breast cancers depend on estrogen for their growth. They are given primarily to women whose tumors express estrogen and/or progesterone receptors. The choice of hormonal therapy depends upon the patient’s menopausal status. Hormonal therapy can cause menstrual irregularities, infertility, hot flashes, decreased libido, vaginal dryness, and bone aches in some women. Side effects include uterine cancer, blood clots in the legs and brittle bones.

Patients can be treated with an estrogen receptor blocker such as tamoxifen. In some premenopausal patients, physicians may choose to add medications that suppress ovarian function to make the patient “post-menopausal” so that they may be candidates for aromatase inhibitor therapy instead. Examples include leuprolide and goserelin.

Postmenopausal patients can be treated with an aromatase inhibitor, which blocks estrogen production, thereby starving cancer cells of the substance they need for growth. Aromatase inhibitors include anastrozole, letrozole and exemestane and have been found to be more effective than tamoxifen for breast cancer treatment.

Postmenopausal women can also be treated with an estrogen receptor blocker like fulvestrant.

There are newer therapies that target specific proteins or molecular pathways that cancer cells use to grow. These therapies are called molecular based therapies and include trastuzumab and tyrosine kinase inhibitors.


This drug halts the growth of breast cancer and can sometimes shrink tumors by binding to the her2neu protein on cancer cells. It is administered intravenously and is sometimes given along with chemotherapy. Studies have shown that this drug can help improve survival rates.

Tyrosine kinase inhibitors

Tyrosine kinase inhibitors are drugs that interfere with cell communication and growth and may prevent tumor growth.

Your Providence Saint John’s breast cancer team will review, in-depth, the side effects you may experience.