In this procedure, biopsy, diagnosis of cancer, and breast removal are completed in a single operation. With this procedure, you and your doctor must agree before surgery that your breast will be removed if the lump is cancerous. Your doctor will explain the full details of a mastectomy (surgical removal of the breast) before biopsy-even though the lump may not be cancerous. In the past, the one-step procedure was thought to be the best way to treat breast cancer. However, studies have shown that treatment can safely follow a biopsy by a week or two-even if the lump is cancerous.