Gina Kolata in the NYT:

As many as 60,000 American women each year are told they have a very early stage of breast cancer — Stage 0, as it is commonly known — a possible precursor to what could be a deadly tumor. And almost every one of the women has either a lumpectomy or a mastectomy, and often a double mastectomy, removing a healthy breast as well.

Yet it now appears that treatment may make no difference in their outcomes. Patients with this condition had close to the same likelihood of dying of breast cancer as women in the general population.