Size indicates how large across the tumor is at its widest point. Doctors measure cancer in millimeters (1 mm = .04 inch) or centimeters (1 cm = .4 inch). Size is used to help determine the stage of the breast cancer.
Size doesn’t tell the whole story, though. All of the cancer’s characteristics are important. A small cancer can be aggressive while a larger cancer is not — or it could be the other way around.
"Size matters when it comes to breast cancer, but size is only one of the personality features on the list. You can have a small cancer that behaves like a bully, or a large cancer that is mild-mannered."-- Marisa Weiss, M.D., chief medical officer, Breastcancer.org