After lumpectomy, all the tissue removed from the breast is examined carefully to see if cancer cells are present in the margins — the normal tissue surrounding the tumor. If cancer cells are found in the margins extending out to the edge of the breast tissue that was removed, your surgeon will perform additional surgery (called re-excision) to remove the remaining cancer.
Re-excision lumpectomy, or simply re-excision, means surgically re-opening the lumpectomy site to try to remove a larger margin of cancer-free tissue. When cancer cells are found close to the edge of the lumpectomy margin, re-excision is necessary to ensure that all the cancer is gone. You may hear your surgeon refer to re-excision as "clearing the margins."