Microscopically, the borders of medullary carcinoma are smooth, rounded, and of "pushing type" (left panel). The border tends to push aside the breast parenchyma and fat rather than infiltrating it. Non-neoplastic glands and fat are therefore not seen within the main body of the tumor. In contrast, the right panel shows the borders of an infiltrating ductal carcinoma with medullary features. The tumor borders freely infiltrate into the surrounding fat. The pattern shown in the right panel is not compatible with a diagnosis of medullary carcinoma.