Hypothesis: increasingly intensive locoregional treatment of breast cancer may promote recurrence.

Evidence is presented compatible with the hypothesis that the inevitable tissue injury to the breast engendered by mastectomy or primary radiotherapy may in itself be a factor facilitating recurrence through a variety of local, regional, and systemic tumor-promoting mechanisms. The potential for tumor enhancement appears to be commensurate with the extent of injury and concerns both local and systemic recurrence. The hypothesis lends itself well to experimental testing. If confirmed, it will point to the importance of minimizing any form of tissue injury in the process of treating primary breast cancer, be it by operation or irradiation and curtailing the extent or intensity of both.