Radiation Therapy With or Without Optional Tamoxifen in Treating Women With Ductal Carcinoma in Situ

OBJECTIVES: * Compare the efficacy of whole breast radiotherapy vs observation with or without optional tamoxifen in decreasing or delaying the appearance of local failure (both invasive and in situ) and preventing the need for mastectomy in women with good-risk ductal carcinoma in situ (DCIS) of the breast. * Compare distant disease-free survival of patients treated with these regimens. OUTLINE: This is a randomized, multicenter study. Patients are stratified according to age (under 50 vs 50 and over), final path margins (negative vs 3-9 mm vs at least 10 mm), mammographic size of primary (no greater than 1 cm vs greater than 1 cm to 2.5 cm), nuclei grade (low vs intermediate), and tamoxifen use (yes vs no). Patients are randomized to 1 of 2 treatment arms. * Arm I: Patients undergo observation and may receive optional oral tamoxifen once daily (at the discretion of the physician) for 5 years. * Arm II: Beginning within 12 weeks after final surgery, patients receive radiotherapy to the whole breast once daily, 5 days a week, for 3.5-5.5 weeks. Patients may receive optional tamoxifen as in arm I. Patients are followed every 3 months for 1 year, every 6 months for 2 years, and then annually thereafter. PROJECTED ACCRUAL: A total of 1,790 patients will be accrued for this study within 6 years.