What are margins in relation to breast cancer?

Surgical success: Breast conserving treatment requires the complete removal of the cancer by lumpectomy, followed by radiation therapy. The pathologist measures the success of lumpectomy by carefully looking at the outer edges of the lumpectomy to be sure no cancer went right to the edge; if it did ("positive margin"), we need to reoperate to remove more breast tissue.

Rim of normal tissue: When a cancer is removed, the pathologist will measure the distance between the edge of the cancer and the surrounding normal breast tissue - this is the margin. Clear margins imply that all of the cancer was removed, but this does not mean it cannot come back. There is not always agreement on how large of a margin is necessary and sometimes it depends on the type of cancer.

Margins: This refers to the amount of normal tissue surrounding the breast cancer that is removed surgically. A positive margin means that all of the tumor was not removed.