Answer: Infiltrating ductal carcinoma. Shaggy groups of three dimensional ductal cells are growing in a desmoplastic stroma. The stromal cells are active-appearing with plump euchromatic nuclei, and they produce abundant mucopolysaccharides (pale purple bubbly material in the stroma). The appearance is histologically (and perhaps biochemically) identical to the reaction in the most active phase of normal wound healing. The ductal cells form irregular cell groupings without the smoothness of the groupings in DCIS. In DCIS the cylindrical duct contours were created by interactions between multiple mutually interactive cell populations, whereas in invasion, the contour of groups of ductal cells have a more random appearance. Not all invasive breast cancers show desmoplasia, and the contour of the groups of infiltrating cancer cells is sometimes very smooth in some breast cancers(see text). Based on the variable appearance of "invasion", it seems likely that there are multiple different mechanisms for invasion.