- Pre- or post-biopsy ipsilateral* breast MRI negative for multicentric disease (i.e., areas of cancer that cannot be removed in a single excision specimen) or other suspicious findings NOTE: *Patients with synchronous bilateral breast cancers who will be treated with radiotherapy to each breast are eligible, provided such treatment can be performed in a manner that avoids overlap between treatment fields. Both sides may be treated with partial breast irradiation (PBI) if the pathologic eligibility criteria are met for both tumors, or only one side may be treated with PBI if the criteria are met for only one tumor.