Technology Assessment: Aromatase Inhibitors for Early Breast Cancer

November 15, 2004

What is a Technology Assessment?

To help doctors give their patients the best possible care, the American Society of Clinical Oncology (ASCO) asks its medical experts to review the latest literature and provide recommendations on the use of medical procedures, devices, or tests in diagnosing or treating cancer. This technology assessment is a patient-friendly version of ASCO's Technology Assessment for Clinicians.

Read the original ASCO Technology Assessment

As you read this technology assessment, please keep in mind that every person treated for cancer is different. These recommendations are not meant to replace your or your doctors' judgment. The final decisions you and your doctors make will be based on your individual circumstances.

Information in ASCO's patient education materials is not intended as medical advice or as a substitute for the treating doctor's own professional judgment; nor does it imply ASCO endorsement of any product or company.

Hormone Treatments for Breast Cancer: Tamoxifen and Aromatase Inhibitors

Hormone therapy for early breast cancer is an adjuvant therapy, which means that it is given in addition to the primary therapy, such as surgery or a combination of surgery and radiation therapy. Adjuvant hormone therapy lowers the likelihood that a woman will have a recurrence of cancer.

Tamoxifen is a standard (widely accepted) adjuvant hormone therapy for breast cancer. It blocks the effects of estrogen on tumor growth and has been proven to prevent recurrence and improve survival in women with early breast cancer. It has been studied for 30 years, and the benefits and side effects are well known.

Aromatase inhibitors (AIs) are a newer class of hormone treatments that are designed to reduce the amount of estrogen in a woman's body. Aromatase is an enzyme the body uses in the production of estrogen. AIs slow or stop the growth of breast cancers that are controlled by estrogen by lowering levels of estrogen in a woman's body. In women who have gone through menopause, AIs can block estrogen production and reduce estrogen levels by more than 90%. To date, AIs have not been studied in women who have not gone through menopause, and there is good reason to believe that they would not be effective in these women.

The three types of AIs discussed in this ASCO Technology Assessment for Patients are anastrozole (Arimidex), letrozole (Femara), and exemestane (Aromasin). Although these drugs are grouped together here, it is not known whether these drugs can be used interchangeably.

The long-term side effects of AIs are not fully established. Early study results suggest that when compared with tamoxifen, AIs may reduce the chance of blood clots and uterine cancer and may increase the risk of osteoporosis and fractures.

At this time, there is a great deal of information about the side effects of AIs when taken for less than five years, but little information is available about a five-year course of treatment. The long-term complications (more than five years) of AI therapy have not been studied. In addition to concerns about osteoporosis, most experts expect that other long-term complications are likely, but more information is needed.

Recommendations

Women with hormone receptor-positive breast cancer who have gone through menopause at the time of diagnosis have two options for adjuvant hormone therapy:

They can begin treatment with tamoxifen for two to five years and switch to an AI for another two to five years
They can begin treatment with an AI for five years

At this time, it is not known which treatment option is better.

It is reasonable for women who have been taking tamoxifen for two or more years to switch to an AI.

What Does This Mean for Women with Breast Cancer?

Women with breast cancer and their doctors must weigh the risks and benefits of all treatment options. The panel recommends that doctors discuss this guideline with their patients and carefully consider each woman's medical circumstances. For some women, the risks and inconvenience of an AI may outweigh the potential benefits.

Women who might be advised to consider using an AI as initial adjuvant therapy:

Women who develop invasive hormone receptor-positive breast cancer while taking an agent such as tamoxifen for breast cancer risk reduction
Women who cannot take tamoxifen because of a high risk of side effects
Women who have tried tamoxifen and had to stop because of side effects
Any woman who has gone through menopause and has hormone receptor-positive breast cancer who would prefer to take an AI instead of tamoxifen as initial treatment

Women who might be advised not to consider using an AI:

Women with hormone receptor-negative breast cancer (these women should also not take tamoxifen)
Women who experience side effects while taking an AI
Women who have not gone through menopause and have functioning ovaries
Women who have gone through menopause and have hormone receptor-positive breast cancer who would prefer to start with tamoxifen and then switch to an AI after a number of years

Women who have not gone through menopause at the time of diagnosis should generally not use an AI as initial adjuvant hormonal therapy outside of a clinical trial, even if they have gone through menopause because of cancer treatment (such as chemotherapy or the suppression or removal of the ovaries). In fact, women whose monthly menstrual periods have stopped may not have gone through menopause, so women should discuss their menopausal status with their doctor. At this time, clinical trials have not yet shown that AIs are effective in this group of women.

Questions to Ask the Doctor

For women who are considering adjuvant therapy:

Is my breast cancer hormone receptor-positive or hormone receptor-negative?
What are the benefits and risks of AIs?
What are the benefits and risks of tamoxifen?
How do the side effects of AIs compare with tamoxifen?
How many years of adjuvant hormone therapy do I need?
Are there any reasons to believe I might not benefit from adjuvant hormone therapy?
Are you sure that I am menopausal?

For women who have completed two to three years of tamoxifen therapy:

Is there a reason I should switch to an AI?
How many more years of hormone therapy would I need if I continue to take tamoxifen?
How many more years of hormone therapy would I need if I switch to an AI?
How will the side effects change if I switch to an AI?

For women who have completed five years of tamoxifen therapy:

Based on my risk of recurrence, do you recommend further hormone therapy with an AI?
What are the possible side effects if I continue therapy with an AI?
How many years would I continue AI therapy?

Glossary

Adjuvant therapy: Treatment that is given in addition to another treatment, such as surgery.

Hormone: A chemical produced by the body, such as estrogen or progesterone, that controls certain actions in the body.

Hormone receptor: Structures where the hormones attach (bind) to cause changes in a cell.

Hormone receptor-positive breast cancer: A type of cancer where the cancer cells use hormones to grow.

Hormone receptor-negative breast cancer: A type of cancer where the cancer cells do not use hormones to grow.

Menopause: The time when a woman stops menstruating (having monthly menstrual periods).

Recurrence: Cancer that comes back after treatment.

For More Information

For a copy of the original technology assessment, please visit www.asco.org or call 703-299-0150.

For more information about cancer, visit Cancer.Net at www.cancer.net. Cancer.Net, ASCO's patient information website, provides oncologist-approved information on more than 50 types of cancer and their treatments, clinical trials, coping, and side effects. Additional resources include a Find an Oncologist database, live chats, message boards, a drug database, and links to patient information organizations. The site is designed to help people with cancer make informed health-care decisions.

Also, on Cancer.net, you can find:

Patient Guides Adapted from the recommendations in ASCO's Clinical Practice Guidelines, these guides offer easy to understand information and helpful resources.

Cancer Advances This series provides summaries of research presented at ASCO's Annual Meeting and Meet the Experts sessions, and published in the Journal of Clinical Oncology (JCO).

Links to abstracts presented at ASCO's Annual Meetings and other educational meetings.

The American Society of Clinical Oncology (ASCO) is the world's leading professional society of multidisciplinary physicians who treat people with cancer. ASCO's more than 20,000 members from the United States and abroad set the standard for patient care worldwide and lead the fight for more effective cancer treatments, increased funding for clinical and translational research, and, ultimately, cures for the many different types of cancer that strike an estimated 10 million people worldwide each year. ASCO publishes the Journal of Clinical Oncology (JCO), the preeminent, peer-reviewed, medical journal on clinical cancer research, and produces Cancer.net (www.cancer.net), an award-winning website providing oncologist-vetted cancer information to help patients and families make informed health-care decisions.

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Last Updated: November 15, 2004