Ustun I, et al. - Since breast cancer can arise from residual breast tissue following a mastectomy, researchers determine the incidence and location of residual breast tissue after modified radical mastectomy in 111 consecutive breast cancer patients. From each quadrant, a 1-cm² tissue sample was obtained under the skin flaps during the operation, following removal of the breast tissue and before skin closure. The presence of any residual breast tissue was determined by analyzing the samples histopathologically. In tissue samples of 12/111 (10.8%) patients, the presence of residual breast tissue was evident, with four having residual tissue in all four quadrants. The most frequently involved location was upper medial quadrant. No breast cancer recurrences were reported after 20 months of follow-up. Mastectomy showed a high likelihood of residual breast tissue being left behind.