Dear DonnaAB: In general, both lumpectomy and mastectomy are acceptable treatments. Many health professionals and women lean toward the lesser surgery as outcomes are similar. However, if you are more comfortable with the mastectomy approach, you should not feel bad if you are in the minority.
I don't understand, with a stage O dcis why your doctors are recommending a mastectomy - sounds a little over the top. I would get a second opinion if I were you.
Hope all goes well.
Liz.