Evidence from 6 major randomized trials comparing outcomes of mastectomy versus BCT for early stage breast cancer finds no significant differences in overall or disease-free survival during intermediate or long-term follow-up to 20 years. Rates of locoregional recurrence are no different at intermediate follow-up for mastectomy versus BCT with radiation; however, statistically significant differences in locoregional recurrence emerge during long-term follow-up, favoring mastectomy over BCT with radiation. Nevertheless, it is not clear whether these delayed recurrences relate to unresected multicentric disease at the time of initial surgery and whether the use of MRI for preoperative evaluation to guide mastectomy would reduce these delayed recurrences.