Lumpectomy is a form of local treatment of ductal in situ and invasive breast cancer.
In this operation, the abnormal lump is removed from your breast. The surgeon also removes a small margin of normal breast tissue from all around the lump, to assure that all of the cancer is removed. Your operation may be followed by radiation therapy.
In a small percentage of ductal cancer in situ cases, some of the underarm lymph nodes are removed to test for possible spread of cancer. This is an entirely different (and diagnostic) surgery called an axillary node dissection. An axillary node dissection is rarely done on the same day as a lumpectomy. It is a separate and diagnostic procedure.
Only the cancerous lump itself and a thin margin of outside tissue is removed.