We teach you about hormonal therapy for breast cancer. Drugs such as tamoxifen and aromatase inhibitors are key treatment options for most breast cancers.

Questions for your Medical Oncologist:

  • What type of hormonal therapy do you recommend?
  • Will I also benefit from chemotherapy?
  • What are the side effects of hormonal therapy?
  • Will I need 5 or 10 years of these medications?
  • Would the genomic assay Oncotype DX be helpful?

What is Hormonal Therapy?

Anti-estrogen (estrogen-blocking) medications, prescribed as pills, are incredibly effective at treating certain types of breast cancer. Hormonal therapy is given to about 70 to 80% of women with breast cancer. Chemotherapy, on the other hand, is a more intense cancer treatment that is generally administered intravenously. Most patients will not need chemotherapy. Many women that do need chemotherapy will also benefit from hormonal therapy. These treatment decisions are complex ones with your medical oncologist. You will make better choices when you are well informed before meeting with your medical oncologist.


Do my “Receptors” suggest Hormonal Therapy?

When the estrogen circulating in your blood stream interacts with a breast cancer that has “Estrogen Receptors” (ER) present on its surface, it tends to flip the ER switch to the “on” or “grow” position for ER Positive tumors. The same can be said to a lesser extent for the “Progesterone Receptor,” if your cancer is found to also be PR positive. Patients with ER+ breast cancers almost always benefit from the anti-estrogen effects of hormonal therapy. These medications can make cancer cells die, or slow down their growth. If a few cancer cells have already spread to other parts of the body, these medications are incredibly effective at preventing these cells from growing and threatening your life in the future. In other words, those who take hormonal therapy for ER+ tumors have a more successful chance at long-term survival when compared to those who do not. This has been proven again and again by hormone therapy clinical trials. Learn the essentials about receptors with our My Tumor Receptors (here).


About 80% of all breast cancers are ER+. Even if your medical oncologist recommends chemotherapy for you, if your tumor is ER+ you will also benefit from up to 10 years of hormonal therapy after chemotherapy. Hormonal therapy is never given during chemotherapy nor during radiation therapy. It is always started afterwards for a number of reasons beyond the scope of this course.


What is “Tamoxifen?”

Tamoxifen is an anti-estrogen medication (pills) that has been used with great success with ER+ cancers for three decades. It is now the primary hormonal therapy for younger, pre-menopausal women. It is also the primary drug for men with breast cancer. It is used for some post-menopausal women.


What are “Aromatase Inhibitors?”

Aromatase inhibitors (AIs) are a class of anti-estrogen medications (pills) that have proven to be slightly more effective than Tamoxifen for post-menopausal women. It is not recommended for younger, pre-menopausal women, except in certain circumstances. The three most common versions are Anastrozole (Arimidex), Letrozole (Femara), and Exemestane (Aromasin).


What are the side effects of Hormonal Therapy?

Side effects vary greatly from one person to the next for both types of hormonal medications. Some have no symptoms at all. Most have very tolerable side effects. Some patients will need to change hormonal therapy medications to find the best balance of cancer benefit versus side effects. Several side effects that are rather common for both tamoxifen and aromatase inhibitors are hot flashes, night sweats, joint pain, and vaginal dryness. Below, we list some of the other specific side effects for both drugs.


Tamoxifen Side Effects:

  • Increased risk of uterine (endometrial) cancer
  • Increased risk of developing blood clots
  • Slows normal bone loss in most women (a “good” side effect)
  • Cannot be taken during pregnancy because of risk of birth defects or fetal death
  • Can temporarily induce menopause in pre-menopausal women.


Aromatase Inhibitor Side Effects:

  • Can worsen bone loss (osteoporosis) in women
  • Muscle and joint aches and pains


Would an “Oncotype DX” assay help me?

Patients who have a small, estrogen receptor positive, HER2 receptor negative tumor, and no evidence of cancer in their lymph nodes may benefit from an Oncotype DX genomic assay. This cutting-edge test looks deeper into your cancer cells to better identify people who may also benefit from chemotherapy with ER+ breast cancers. The decision to undergo chemotherapy, in addition to hormonal therapy, is a complicated one. Your medical oncologist uses many factors to help decide if you will benefit from chemotherapy. An Oncotype DX analysis of a portion of your breast cancer tissue can be instrumental in this decision. Review our video lesson on Genomic Testing (here) to learn more about these “cutting-edge” advances in breast cancer treatment.


Would a “Breast Cancer Index” assay help me?

Recent clinical trials have shown that extending hormonal therapy from 5 years to 10 years can reduce risk of recurrence/death by about 3 to 5%. Ten years of hormonal therapy is becoming the new standard of care.


A new genomic test called the “Breast Cancer Index” attempts to predict the chance of breast cancer recurrence during this extended hormone therapy period between 5 to 10 years. It can help women determine if there is benefit from this extended period of hormonal medications. It is not currently FDA approved, but may be available to you and your medical oncologist to help decide if you can avoid the extra five years of hormonal therapy.


Patient-Friendly References:

  • cancer.net
    An excellent overview “Hormonal Therapy for Early-Stage Hormone Receptor-Positive Breast Cancer” is located (here). The American Society of Clinical Oncologists is a leading organization of clinicians who care for people living with cancer.


  • NCCN Guidelines for Patients
    You will find well-organized guides (here) on breast cancer treatment by stage. Follow the prompts to breast cancer and then “stage” in the dropdown menus. The NCCN is a consortium of organizations and governmental agencies to promote quality breast cancer care.


A good overview of “Hormonal Therapy” is located (here). This site is created for patients by the American Society of Breast Surgeons.


  • jamanetwork.com
    This “Patient Page” (here) outlines “Hormone Therapy-Related Hot Flashes and Their Management” and is written for patients. The Journal of the American Medical Association (JAMA Oncology) is a publication of the largest physicians association in the United States.


More Detailed References:

If you want to get deep into the details, this free 200-page pdf document (here) has guidelines to help clinicians to make treatment recommendations about nearly all aspects of breast cancer. You can easily register (here) as a non-professional to get access and more information about breast cancer. The National Comprehensive Cancer Network is the leading organization in developing clinical guidelines.


To estimate the risk of cancer recurring in other parts of the body (distant recurrence) after 5 years of hormonal therapy, try this calculator tool. This information can be helpful in consultation with your medical oncologist as to the benefits and risks of taking hormonal therapy beyond 5 years. The Clinical Treatment Score Post–5 Years (CTS5) was developed from an analysis of data of more than 11,000 women from two major clinical trials, using readily available disease measures. The patients had received hormonal therapy for 5 years. It was published in the Journal of Clinical Oncology in August 2018.



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