We hypothesize that variations in anatomic location of the arm lymphatic drainage system put the arm lymphatics at risk for disruption during a SLNB and / or ALND. Therefore, mapping the drainage of the arm during the procedure would decrease the likelihood of inadvertent disruption of the lymphatics and the subsequent development of lymphedema. A combination of radioactivity and blue dye will be used.

Mapping Procedure:

Each patient will receive an injection of 1.0 mCi of technetium-99m sulfur colloid into the normal breast tissue surrounding the primary cancer or biopsy cavity directed subareolar or around the tumor.

If the radioactive SLN cannot be located prior to incision via gamma probe then the blue dye will be used in the breast either in the subareolar plexus or peritumorally at the discretion of the surgeon. For this contingency (expected to occur <3% of the time), the blue dye will be used in the breast (and NOT the arm), as the prime concern is locating the SLN for staging.

If the blue dye is unnecessary to find the sentinel node draining from the breast, then it will be injected dermally in the upper inner arm along the Biceps groove of the ipsilateral arm in order to locate the draining lymphatics from the arm. No more than 5cc of blue dye will be injected in either the subareolar plexus, peritumorally (intraparenchymal or dermally), or dermally in the patient's ipsilateral arm dependent upon the contingencies stated above. Site of all injections (radioactivity and/or blue dye) will be recorded.

Inclusion Criteria:

• 18-100 years old
• Not pregnant or breastfeeding
• Breast cancer requiring lymph node evaluation for the ipsilateral or contralateral breast OR prophylactic mastectomy
• Willing participation following an informed consent process

Exclusion Criteria:

• Patient < 18 y/o or > 100 y/o
• Pregnant or breastfeeding
• If a pregnant female should be diagnosed with breast cancer an exception would be considered on a case to case basis.