What is "early-stage" breast cancer?

Good prognosis: "early stage" means it was detected early. That generally means a relatively small (amenable to lumpectomy/breast conservation) with no or minimal lymph node involvement. The earlier a cancer is detected the more options for treatment and the better the prognosis.

Usually stage 0 or 1: The breast is composed of glands that can produce milk (lobules), tubes that transport the milk to the nipple (ducts), and fatty tissue. Cancer may begin in the lobules or ducts. If it is only found inside these structures, the stage is 0 (zero). If it grows out of the lobules or ducts into the fatty tissue, but is not in the lymph nodes, it is stage 1 (one).