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Basic Information on Tamoxifen

Tamoxifen is a drug taken orally in pill form. For over a quarter of a century, physicians haveprescribed tamoxifen to help treat patients with advanced breast cancer. In the 1990s,

physicians began using tamoxifen to treat early stage breast cancer after breast surgery(lumpectomy ormastectomy). Tamoxifen has been shown to help prevent the original breast

cancer from returning after breast surgery while also hindering the development of newcancers in the opposite breast.

In late 1998, tamoxifen became the first drug to be approved by the U.S. Food and Drug

Administration (FDA) to prevent breast cancer after research showed it reduced the chances

of developing breast cancer by 50% in women at high risk.

How Does Tamoxifen Work?

To grow and reproduce, breast cancer cells require the female hormone estrogen. Tamoxifen

is an "anti-estrogen" and works by competing with estrogen to bind to estrogen receptors in

breast cancer cells. Tamoxifen is formally known as a selective estrogen receptor modulator(SERM). By blocking estrogen in the breast, tamoxifen helps slow the growth and

reproduction of breast cancer cells.

While tamoxifen fights estrogen in breast cancer cells, it also mimics the positive effects of

estrogen in other body systems. Post-menopausal women who take tamoxifen may decreasetheir risk ofheart disease orosteoporosis (a degenerative bone disease) without having to use

hormone replacement therapy (HRT).

Who is a Candidate for Tamoxifen Therapy?

A womans physician will determine whether she is a candidate for treatment with tamoxifen.Patients who have been treated with tamoxifen include:

y Women with Stage III orStage IV breast cancer (tamoxifen is usually prescribed inconjunction with chemotherapy or other treatment)

y Women with early stage breast cancer after breast surgery (lumpectomy ormastectomy)

y Women who have been identified to be at high riskof developing breast cancerTamoxifen has been shown to be more beneficial for women whose breast cancer cells

contain estrogen receptors (ER). An "ER-positive cell" (one that has estrogen receptors) may

contain hundreds or thousands of estrogen receptors near the cell nucleus where the genetic

information is stored. Because tamoxifen works by binding to estrogen receptors in cells thusblocking the body's own supply of estrogen from reaching the receptors, women with ER-

positive receptors typically respond better to tamoxifen therapy than women with ER-negative receptors. A tissue sample obtained frombreast biopsy may be analyzed to

determine whether cancer cells are ER-positive or ER-negative. Note: the absence of

estrogen receptors in breast cancer cells does not necessarily mean that tamoxifen will be

ineffective. Researchers are still investigating how tamoxifen acts on ER-negative cells.

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Several studies have also shown the benefit of tamoxifen in preventing breast cancer is age-related. Women under 40 years of age typically show the least response to tamoxifen,

women between the ages of 40 and 50 years of age show some response, and women over 50typically benefit most from tamoxifen. In fact, early-stage breast cancer patients over 50

years of age who are treated with tamoxifen may be able to significantly reduce (or

sometimes completely eliminate) the size of their breast tumors so that surgeons may perform

lumpectomy instead ofmastectomy. Researchers are not certain why young women do notrespond as well to tamoxifen but believe it may be related to the amount of estrogen produced

in their body. When a woman reaches menopause (typically around 50 years of age), her

body stops producing estrogen.

Typical profiles of women who take tamoxifen to help prevent breast cancer:

Age 35 or older and any of the following combination of factors:

y One first degree relative (such as mother or sister) with a history of breast cancer, 2 ormore benignbiopsies, and a history of a breast biopsy showing atypical hyperplasia;

or

y At least 2 first degree relatives with a history of breast cancer, and a personal historyof at least one breast biopsy; or

y Lobular carcinoma in situ (LCIS, also called lobular neoplasia), a condition thatsignificantly increases the risk for breast cancer

Age 40 or older and any of the following combination of factors:

y One first degree relative with a history of breast cancer; 2 or more benign biopsies,age 25 or older at first live birth, and age 11 or younger at menarche (first

menstruation); or

y At least 2 first degree relatives with a history of breast cancer, and age 19 or youngerat first live birth; or

y One first degree relative with a history of breast cancer, and a personal history ofbreast biopsy showing atypical hyperplasia

Age 45 or older and any of the following combination of factors:

y At least 2 first degree relatives with a history of breast cancer and age 24 or youngerat first live birth; or

y One first degree relative with a history of breast cancer with a personal history of abenign breast biopsy, age 11 or younger at menarche and age 20 or older at first live

birth.

Age 50 older and any of the following combination of factors:

y At least 2 first degree relative with a history of breast cancer; ory History of one breast biopsy showing atypical hyperplasia, and age 30 or older at first

live birth and age 11 or younger at menarche; or

y History of at least two breast biopsies with a history of atypical hyperplasia, and age30 or older at first live birth.

Age 55 or older and any of the following combination of factors:

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y One first degree relative with a history of breast cancer with a personal history ofbenign breast biopsy, and age 11 or younger at menarche; or

y History of at least 2 breast biopsies with a history of atypical hyperplasia, and age 20or older at first live birth.

Age 60 or older and:

y Five-year predicted risk of breast cancer 1.67%, as calculated by the Gail Model(the Gail Model was developed by the National Cancer Institute and researchers from

the National Surgical Adjuvant Breast and Bowel Project). Click here for a patient

version of the Breast Cancer Risk Assessment Tool.

Source: AstraZeneca, manufacturer of Nolvadex (brand name of tamoxifen)