Breast cancer is the most common cancer among women worldwide. The present study was conducted on 50 female cases of mammary in situ and invasive duct carcinoma. All studied cases of invasive duct carcinoma were graded as grade I, II and III according to Elston/Nottingham modification of Bloom-Richardson system. All cases diagnosed as duct carcinoma in situ, with or without focal invasion, as well as invasive duct carcinoma grade II and most of invasive duct carcinoma grade I cases showed weak immunostaining as opposed to invasive duct carcinoma grade III in which 71.4% of its cases showed strong immunostaining. There was a highly significant correlation between CD10 immunostaining intensity and tumor grade. No significant correlation could be achieved between CD10 immunostaining intensity and either patients age, tumor size, lymph node metastasis or hormone profile.