Although magnetic resonance imaging (MRI) is exquisitely sensitive for detecting breast cancer, its precise clinical benefit in the routine preoperative setting is uncertain, and determination of its appropriate use to date has been challenging.1 Early randomized prospective trials were hindered by low numbers, wide variation in imaging quality, and inconsistencies in incorporating MRI findings into treatment planning. Larger, more recent, retrospective trials have reported correlations between use of breast MRI and increased mastectomy rates but have been significantly limited by not controlling for key variables that are independently associated with mastectomy rates.2-4 Women who undergo preoperative MRI comprise a distinct subset of patients: they are more likely to be young, at high risk, have dense breast tissue, have genetic mutations, have more aggressive tumor subtypes, be seen at academic subspecialized centers that offer advanced reconstructive surgical techniques, and be in a higher socioeconomic status group than those who do not undergo MRI. These factors themselves are known to be associated with higher rates of mastectomies2,5; thus, failure to control for these variables is a significant limitation of retrospective studies seeking meaningful correlations between MRI use and outcomes. Most important, correlation does not imply causation.