In patients already scheduled to undergo sentinel lymph node dissection in the operating room, the investigators will first perform an axillary ultrasound guided core needle biopsy percutaneously. Patients will have already undergone prior injection of radioisotope and blue dye and as a standard procedure or the sentinel lymph node dissection. After induction of anesthesia, the investigators will identify the location of the sentinel node with a gamma probe to identify the "pre-incision hot spot." Axillary ultrasound will then be used to identify the location of the lymph node and a percutaneous core needle biopsy of the targeted lymph node will be performed. The core biopsy specimen will be evaluated for the presence of blue staining and radioisotope uptake intraoperatively. The core biopsy specimen will then will be sent for pathologic analysis. The percutaneous biopsy should take about 10 minutes of additional operating room time. The operation will then proceed as planned with dissection and removal of the remaining sentinel node(s). Core samples and sentinel lymph nodes will be evaluated in a similar fashion per existing sentinel node protocol.
