The basic components of the mammary gland are the alveoli (hollow cavities, a few millimetres large) lined with milk-secreting cuboidal cells and surrounded by myoepithelial cells. These alveoli join up to form groups known as lobules, and each lobule has a lactiferous duct that drains into openings in the nipple.

The most common tumors are Lobular Carcinoma and Ductal Carcinoma, they come in two forms, infiltrating ductal carcinoma, an invasive cell type (the cancerous cells invade and replace the surrounding normal tissue inside the breast); and ductal carcinoma in situ, a noninvasive cancer ( In situ means “in place” and refers to the fact that the cancer has not moved out of the duct and into any surrounding tissue)

Besides there are less frequent types as Medullary carcinoma, Tubular/cribriform carcinoma, Papillary carcinoma, Metaplastic carcinoma, etc. The name is given according to the region where they originated.