Among the 93 surgical specimens of stage I breast cancer treated by breast preserving operation, surgical margins were less than 10mm in 23 (25%) cases because of intraductal spread. Such tumors with extensive intraductal component, however, were frequently positive for estrogen receptor (ER). Possible risk factors for local failure have been studied in an attempt to exclude high-risk patients not suitable for breast preserving operation. The results so far obtained suggest that biological markers such as c-erb B-2 or PS2 proteins may provide useful informations to select patients who are most likely to recur. In addition, adjuvant endocrine therapy may be recommended for the patients treated by breast preserving operation.