The bulbs are too small to be seen on this diagram. Most of the breast cancers form initially in the ducts of the breast. When the disease is confined to the ducts it is called intraductal cancer. These types of cancers do not have the potential of spreading and are curable. The picture on the right shows where breast cancers occur in a woman's breast.
Doctors routinely divide the breast into quadrants as shown in the drawing below.
The lower-inner quadrant has the lowest number of breast ducts and therefor has the lowest incidence of breast cancer. When the cancer cells break out of the duct, the cancer becomes an infiltrating ductal carcinoma . All ducts lead to the nipple , which is centered in the areola, a dark area of skin in the middle of the breast. The actual breast is composed of fat and breast tissue. The pecs are shown quite nicely in the drawing above.