Anastrozole or Tamoxifen in Treating Postmenopausal Women With Ductal Carcinoma in Situ Who Are Undergoing Lumpectomy and Radiation Therapy

RATIONALE: Estrogen can stimulate the growth of breast cancer cells. Tamoxifen may fight breast cancer by blocking the use of estrogen. Anastrozole may fight breast cancer by decreasing estrogen production. It is not yet known whether anastrozole is more effective than tamoxifen in preventing the recurrence of breast cancer. PURPOSE: This randomized phase III trial is studying anastrozole to see how well it works compared to tamoxifen in preventing the recurrence of breast cancer in postmenopausal women with ductal carcinoma in situ who are undergoing lumpectomy and radiation therapy.