Ductal carcinoma of the breast surrounded by a fibrous stromal sheath. Depicted is a single duct containing an intraductal carcinoma. White arrows show lumen-like structures; however, normal epithelial cell polarity is lost. Black arrows show delineation between tumorigenic mammary epithelial cells and stromal tissue. The asterisk shows stromal sheath encapsulating the ductal carcinoma in situ. Magnification: 400×. From University of Connecticut's Virtual Pathology Museum http://pathweb.uchc.edu.