Information available from NSABP protocols has contributed to an altered biological perception of breast cancer. The results of these studies lend support to a hypothesis which postulates that alterations in the loco-regional treatment of primary breast cancer will not change the natural history of the disease relative to distant metastasis and survivorship. Data from NSABP Protocol B-04 indicate that radical mastectomy provides no advantage over total mastectomy in clinically node-negative patients. Since 39% of this population had histologically positive nodes it may be concluded that leaving histologically positive nodes untreated results in no disadvantage. NSABP Protocol B-04 made available the scientific rationale for the study of breast-preserving operations in which the clinical significance of multicentricity will be determined. Although there is a sound scientific basis for the consideration of segmental mastectomy, there are no data available to justify the utilization of the procedure outside the context of a clinical trial. With the increased popularity and implementation of breast-preserving operations without the necessary supporting data, a potentially dangerous situation has been created which threatens to undermine the clinical trial process.