Healthy milk ducts in a woman's breast, micro- endoscope view. Milk (lactiferous) ducts are the tubes through which milk reaches the nipple from the secretory lobules within a breast. The ducts are the most common site for the development of breast cancer. By passing an ultra-fine endoscope through the opening in a nipple, doctors can inspect the milk ducts directly, allowing them to diagnose any change much earlier than with conventional techniques. The earlier a tumour is discovered, the greater the chances of a cure. This endoscope is being developed by the Imperial Cancer Research Fund at Guy's Hospital, London, England.