Comparing an Operation to Monitoring, With or Without Endocrine Therapy (COMET) Trial For Low Risk DCIS

Inclusion Criteria: * Diagnosis of unilateral, bilateral, unifocal, multifocal, or multicentric DCIS without invasive breast cancer (date of diagnosis defined as the date of the first pathology report that diagnosed the patient with DCIS) OR: atypia verging on DCIS OR: DCIS + LCIS (mix and/or separate locations in the same breast) * A patient who has had a lumpectomy or partial mastectomy with margins positive for DCIS (i.e. \<2mm/ink on tumor) as part of their treatment for a current DCIS diagnosis is also eligible (post-excision bilateral mammogram required at enrollment to establish a new baseline) * No previous DCIS or invasive breast cancer in ipsilateral breast 5 years prior to current DCIS diagnosis * 40 years of age or older at time of DCIS diagnosis * ECOG performance status 0 or 1 * No contraindication for surgery * Baseline imaging (must include dimensions): * Unilateral DCIS: contralateral normal mammogram ≤ 6 months of registration and ipsilateral breast imaging ≤ 120 days of registration (must include ipsilateral mammogram; can also include ultrasound or breast MRI) * Bilateral DCIS: bilateral breast imaging ≤ 120 days of registration (must include bilateral mammogram; can also include ultrasound or breast MRI) * DCIS s/p lumpectomy: post excision mammogram on side of excision ≤ 60 days of registration * Pathologic criteria: * Any grade I DCIS (irrespective of necrosis/comedonecrosis) * Any grade II DCIS (irrespective of necrosis/comedonecrosis) *…