Breast Cancer Medications

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Breast cancer risk-reducing medications may decrease the risk of primary breast cancer in some women aged 35 and older who are at increased risk of breast cancer. While there is no specific cutoff to define that increased risk, most studies define it as at least a 3% chance of developing it in five years. So how is that increased risk determined? The answer is a complex one. Obviously, family history is an important consideration, especially if there is a familial genetic mutation, for example the rare BRCA mutation. Other factors include age at which menstruation began and reproductive factors such as the number of children and pregnancies. Another risk factor is very dense breasts as seen on mammography, which make mammographic detection of early, small tumors much more difficult.

There are multiple breast cancer risk estimation models that have been developed, none of which is clearly superior to the others. I have listed some of them at the end of this column. Which tool to use and how to interpret the results should be discussed with a doctor and/or genetic counselor. The medications that may be used for breast cancer risk reduction include selective estrogen receptor modulators (SERMs) such as tamoxifen and raloxifene, and aromatase inhibitors (AIs), such as Arimidex (anastrozole), Aromasin (exemestane), and Femora (letrozole). SERMs are antiestrogens that block the effects of estrogen, and AIs block the enzyme aromatase that converts the hormone androgen into estrogen in the ovary. Only tamoxifen is indicted for use in premenopausal women. AIs are most effective in postmenopausal women, more effective than SERMs, but they cannot block the production of estrogen in the ovaries in premenopausal women unless a medication to suppress the ovaries is also used, for example Lupron (leuprolide) and Zoladex (goserelin).

These medications may reduce a person’s risk of certain types of breast cancer, but there is no evidence that they reduce the risk of estrogen-receptor (ER) negative breast cancer. Women taking these medications should still undergo regular breast cancer screening, and younger women considering pregnancy should not take them as they may be harmful to a developing fetus. The typical duration of treatment is five years. Of course, like all medications, they do have side effects. For example, for postmenopausal women who still have a uterus, raloxifene is a better choice than tamoxifen because it has a lower risk of uterine cancer. SERMs may also cause hot flashes and increase the risk of blood clots in the legs and lungs, especially in women who smoke. The goal in considering use of these medications is to determine who is likely to have the greatest benefit from them, and whether or not the benefits outweigh the risks. The use of these medications is constantly evolving.

Risk estimation resources include:

The National Cancer Institute Tool, known as the Gall model ( www.bcrisktool.cancer.gov/ ), the Breast Cancer Surveillance Consortium Risk Calculator (tools.bcsc-scc.org/BC5yearRisk/), the IBIS Breast Cancer Risk Evaluation Tool ( www.ems-trials.org/riskevaluator/), and the Breast and Ovarian Analysis Disease Incidence and Carrier Estimation Algorithm ( www.ccge.medschl.cam.ac.uk/boadicea/ ).

For more information go to:

uspreventiveservicestaskforce.org/uspstf/recommendation/breast-cancer-medications-for-risk-reduction

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 By Peter Galvin, MD

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