A breast biopsy is a procedure in which a small sample of breast tissue is removed for examination under a microscope .It is typically done when a lump or abnormality is detected in the breast, and is used to determine whether the tissue is cancerous or benign (non-cancerous). Core needle biopsy is commonly done as an outpatient procedure under local anaesthesia. A breast biopsy is generally a safe procedure, and is often the best way to diagnose breast cancer or rule it out.