What is Breast Cancer?



Breasts are made up of glands that make milk surrounded by fatty tissue. The part of the glands where milk is made are called lobules and the tubes that carry the milk to the nipple are called ducts. Cancer can start in either the lobules or the ducts.



The breast is made up of cells so small they can only be seen with a microscope. Cells divide and replace cells that have died. There are controls that tell the cells when to stop dividing.



When these controls no longer work, cells do not stop dividing. The clump of cells is called a tumor. When the cells stay where they started, the tumor is called in situ cancer.



When the cancer begins to spread away from where they start, the tumor is called invasive cancer. From here cells from the cancer can break off and spread to other parts of the body.