Purpose : Breast cancer with BRCA1 variation has similar microscopic appearance with medullary cancer, and has pushing margins. These cases are classified as infiltrating ductal carcinoma with medullary general, medullary cancer expresses p53 and negative HER-2/neu. Positive ER is related to good prognosis, and well differentiated cancer is related to positive predictive value. Based on these correlations, the study was designed to make differentiation between medullary cancer and infiltrating ductal carcinoma with medullary feature with expression of ER, p53, and HER-2/neu. Material and Methods : Specimen of 10 medullary cancer and 20 infiltrating ductal carcinoma with medullary feature, which were obtained from biopsy or operation at breast clinic in Soonchunhyang university Cheonan hospital underwent immunohistochemistry stain.Results : ER expression in medullary cancer was negative in 9 out of 10 cases. In infiltrating ductal carcinoma with medullary feature, it was negative in 14 out of 20 cases, and there was expression of grade 3 in 5 cases. Expression of p53 in medullary cancer was grade 1 in 5, and grade 3 in 5 among 10 cases. In infiltrating ductal carcinoma with medullary feature, it was grade 1 in 7, and grade 3 in 11 among 20 cases. The expression of HER-2/neu in medullary cancer was score 0 in 2, and score 3 in 4 among 10 cases. It was expressed as score 0 in 8, and score 3 in 10 among 20 cases with infiltrating ductal carcinoma with medullary feature. Conclusion : Expression of p53 and HER-2/neu was not useful in differentiating medullary cancer and infiltrating ductal carcinoma with medullary feature. ER was useful only in cases with positive ER expression. Microscopic findings of necrosis and stromal feature, or ultrasonographic findings of tumor margin was considered to be more valuable in discriminating the 2 diseases.