In the early 1890s, Dr William Halsted developed radical mastectomy for breast cancer. Surgeons performed the Halsted procedure for more than 80 years even though there was little systematic evidence for its success. Then a new breed of scholars subjected the procedure to formal methods of evaluation unknown to Halsted.1 The methods—randomized controlled trials (RCTs) principal among them—led to a surprise: radical mastectomy had no advantage over simpler forms of treatment.2