The physician identifies a palpable mass in one breast, and the patient is scheduled for a "Lumpectomy." The reason that "Lumpectomy" for breast lumps can be safely performed in some patients is that the breast is divided into multiple lobes, each of which contains a separate duct system with connecting lobules. The normal breast usually contains how many lobes?

The normal breast contains 15 to 25 lobes. Each lobe can be thought of as having an "inveed tree" composed of a "trunk" made of the lactiferous duct, "branches" made of smaller ducts that feed into the lactiferous duct, and "leaves" made of lobular tissue. Depending on the clinical setting, surgeons will also sometimes excise the duct system under the nipple along with the lump in the breast.