 Single center, blinded, randomized, parallel-group, comparative study of Lymphoseek and 99mTc-SC in the preoperative and intraoperative detection of lymph nodes in subjects with known breast cancer. All subjects will receive a single dose of 50 μg Lymphoseek radiolabeled with 0.5 mCi Tc 99m or 0.5 mCi of 99mTc-SC. Subjects may also receive up to 1 mL of vital blue dye VBD as a companion ILM agent. All radio-labeled agents will be administered in a single intradermal injection. 