The histologic responses of breast tissue to injury are limited. Needle core biopsies of the breast are associated with displacement of tumor cells, and the incidence of tumor displacement decreases as the time interval between needle core biopsy and subsequent excision increases. This suggests that displaced tumor cells are destroyed by reparative processes induced by tissue injury. Residual tumor in a lumpectomy site may also be subjected to the same destructive processes associated with tissue repair. A total of 259 consecutive cases of infiltrating ductal carcinoma with margin-positive lumpectomies and their associated reexcision specimens obtained over a 7-year period were analyzed for the presence, type, and quantity of residual disease. The overall incidence of residual disease was 69%. Residual infiltrating ductal carcinoma was present in 35% of cases, and residual ductal carcinoma in situ was present in 50%. An increased time interval between lumpectomy and reexcision was associated with a decreased incidence of residual infiltrating carcinoma (p <0.0043); this decrease was not found associated with ductal carcinoma in situ. These findings suggest that the host response to injury may destroy residual infiltrating carcinoma cells in some margin-positive cases.