In patients with breast cancer who had undergone breast conservative treatment involving lumpectomy, axillary lymph node dissection and irradiation, the surgical results and risk factors for remaining cancer foci in the conserved breast were investigated. This form of surgery was performed in 25 patients with T1,N0,-Ia,M0 breast cancer. The cut end of the resected specimen was histopathologically positive for cancer cells in 48% of the patients, but there has been no local or distant recurrence in any patient to date with a mean follow-up period of 17.2 months after surgery. In most breasts resected after lumpectomy, slight cancer foci remained in mammary glands at the sites within 1.0cm distant from the cut end. Extensive remaining cancer lesions were found among cases with advanced intraductal spread or central necrosis in the intraductal foci. The above findings indicate that breast conservative treatment by lumpectomy may result in histopathologically remaining cancer foci, although these can be controlled by irradiation therapy. However, application for this treatment requires much caution when severe intraductal spread or central necrosis is present in the intraductal foci, because extensive cancer foci may remain postoperatively in such cases.