By the time a cancer is big enough to be seen on a mammogram, it is usually eight years old, has 500 million cells, and is approximate 1/4 inch long. (7) It has been large enough to metastasize for a year or more. Some breast cancers never metastasize no matter how large they get.
It's better to let it get to the size of a grapefruit that way you know it's really there and know where to cut it out...