The study was stopped after 69 subjects were enrolled because of poor accrual.

Women with hormone-receptor positive breast cancer are typically treated with hormone therapy as part of their treatment after surgery. In the past few years it has been found that treatment with aromatase inhibitors is superior to tamoxifen in postmenopausal women. Tamoxifen is still used for premenopausal women, however, because aromatase inhibitors are not effective in women who have functioning ovaries. Some women are premenopausal at the time they are diagnosed with breast cancer, but then stop having menstrual periods when they are treated with chemotherapy. It is unclear if these women can also be treated safely with aromatase inhibitors.

In this clinical trial the researchers will try to answer this question. Women with hormone receptor positive breast cancer who become postmenopausal with chemotherapy will be invited to participate in this study. Each woman will be treated with one of the aromatase inhibitors, anastrozole (Arimidex), and then carefully monitored to ensure that her ovaries do not start making estrogen. If her estrogen level remains low, then she will continued to be followed for 18 months. If the level increases to the level typically seen in premenopausal women, however, then she will stop taking part in this study.

The study will also evaluate multiple factors that may help doctors predict who will tolerate the therapy without having their ovaries start making estrogen again. Some of the factors to be evaluated include other hormone levels (blood tests) as well as family history of early menopause (mother, sisters). In addition, changes in certain genes that affect how patients' bodies handle chemotherapy drugs will be tested to see if they affect whether or not patients recover ovarian function. Overall, the purpose of the study is to determine which patients who become postmenopausal from chemotherapy are likely to tolerate aromatase inhibitor treatment safely, and how often the patients' ovarian function needs to be tested during treatment.

Inclusion Criteria:

To be eligible for this study:

1. You must be at least 18 years of age and not older than 60 years of age
2. You have breast cancer which was confined to the breast and lymph nodes under the arm, and have no evidence of cancer elsewhere
3. You must have had surgical removal of your tumor, and if indicated, radiation therapy must have been completed or planned
4. Your tumor must express estrogen and/or progesterone receptors
5. You must have had a menstrual period within 6 months before starting chemotherapy for your breast cancer.
6. You must have been treated with a chemotherapy regimen that includes cyclophosphamide (Cytoxan). Your menstrual periods must have stopped for at least 8 weeks starting during or after chemotherapy.

Exclusion Criteria:

You are not eligible to participate in this study if:

1. Your ovaries have been surgically removed, treated with radiation therapy, or if you are taking medications (Zoladex™ or Lupron™) to block the function of your ovaries.

Initiated treatment with Anastrozole, 1 mg orally daily.

All Adverse Events (AEs) will be captured while each patient is taking study medication and for 30 days after the patient discontinues study medication and/or trial participation.

Because of poor accrual, the trial was closed after 69 of a planned 150 patients were enrolled.