Suppression of Ovarian Function With Either Tamoxifen or Exemestane Compared With Tamoxifen Alone in Treating Premenopausal Women With Hormone-Responsive Breast Cancer

Inclusion Criteria: * Premenopausal women (estradiol \[E2\] in the premenopausal range \[according to institution parameters\]) who meet the following criteria: * Patients who did not receive chemotherapy should be randomized within 12 weeks after definitive surgery; such patients should have estradiol (E2) in the premenopausal range following surgery; the only patients who do not require testing of estradiol (E2) to confirm premenopausal status are those who have been menstruating regularly during the 6 months prior to randomization and have not used any form of hormonal contraception or any other hormonal treatments during the 6 months prior to randomization * Patients who received prior adjuvant and/or neoadjuvant chemotherapy should be randomized after completing chemotherapy and within 8 months of the final dose of chemotherapy as soon as premenopausal status is confirmed; all such patients should have premenopausal status confirmed by an estradiol (E2) in the premenopausal range between 2 weeks and 8 months after completing chemotherapy * Adjuvant trastuzumab (Herceptin ®) is allowable, and is not considered to be chemotherapy for eligibility timing determination * Patients with temporary chemotherapy-induced amenorrhea who regain premenopausal status within eight months of the final dose of chemotherapy are eligible; (please note that some patients taking tamoxifen or aromatase inhibitors, even without evidence of menses, may have ovarian function recovery fo…