The study found that at the Mayo Clinic in Rochester, Minn., the percentage of women opting for mastectomy rather than lumpectomy began rising sharply after 2003, in reversal of a previously downward trend.

It is not clear that the experience at the clinic reflects that of the entire nation, though there is some evidence pointing to a wider tendency.

And one possible explanation is that magnetic resonance imaging, which is relatively new, detects more possibly cancerous growths than does mammography. That could be causing patients and doctors to conclude that a lumpectomy, which removes just the part of the breast containing the primary tumor, may not be sufficient.
http://www.nytimes.com/2008/05/16/health...