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 margin of tissue that is cancer-free. You may hear your surgeon refer to re-excision as "clearing the margins."
How large do the margins need to be? In February 2014, the American Society for Radiation Oncology and the Society of Surgical Oncology issued new guidelines saying that clear margins, no matter how small as long as there was no ink on the cancer tumor, should be the standard for lumpectomy surgery.