Why is it that some patients who are in stage 1 dcis have to have a partial mastectomy followed by radiation?

Stage 0 breast ca. DCIS is a stage 0 breast cancer. A lumpectomy is only comparable to a mastectomy when the lumpectomy is followed by radiation. Otherwise the risk of the cancer recurring in the same breast is higher. For some older patients (over 70) radiation may be optional after a lumpectomy. .