Invasive breast cancer is also called infiltrating cancer because the cancer grows outside the ducts or lobules where it started. They are named for the way the cells look under a microscope. Tubular cancer cells look like tubes. Medullary cancer looks like brain tissue and can be aggressive or less aggressive. Mucinous cancer is a kind of infiltrating ductal cancer that makes mucous.
Papillary cancer has cells that stick out in finger-like projections called papules.
You might also be told that the cancer cells are well differentiated or poorly differentiated . Well-differentiated cells look more like normal cells and usually mean the cancer is less aggressive. Poorly differentiated means the cells have a wild look about them and usually means the cancer is more aggressive. Staging After the tests are done and the lab reports have determined what kind of breast cancer you have, your doctor will stage the tumor. This classification is important in deciding what treatment is best for you.