This study proposes the use of a newly developed experimental radioactive dye (radiolabeled methylene blue). On the day of surgery, the patient receives a single injection of the experimental radioactive dye after anesthesia. The injection will be in the location around the breast tumor. The surgeon makes a small cut in the armpit on the side of the cancer and is able to locate the lymh nodes that collect drainage from the cancerous area by detecting lymph nodes with higher radioactivity using a hand-held detector (a Geiger counter-like device) and/or visually identifying lymph nodes stained blue by the dye. These lymph nodes are then removed and analyzed by pathologists for the presence of cancer.