Researchers are trying to determine if the Mayo marker is easily seen with ultrasound making it easier, faster, and more accurate for preoperative localization of the biopsied positive lymph node.

Nonrandomized clinical trial to evaluate the Mayo-designed marker for ultrasound conspicuity at the time of preoperative ultrasound-guided localization.

Study participants are breast cancer patients with pathology-proven metastatic axillary lymph nodes. Per standard of care, a biopsy marker will have already been associated with the positive lymph node. 10 such patients scheduled for surgery at Mayo Clinic Rochester, MN with Dr. James Jakub will be enrolled. Preoperative radioactive seed localization will proceed as usual, but the marker will be additionally loaded with the seed into the needle using standard protocol. Before surgery, ultrasound will be performed to evaluate the marker.

Inclusion Criteria:

• Patient 18 years or older with breast cancer and biopsy-proven malignant involvement of an axillary lymph node
• Surgical management involves preoperative radioactive seed localization of a previously identified positive axillary lymph node
• Surgery will be performed by Dr. James Jakub at Mayo Clinic Rochester, MN
• Radioactive seed localization of an axillary lymph node.
• No contraception is necessary or required.
• English speaking

Exclusion Criteria:

• Scheduled for only radioactive seed localizations in the breast (as opposed to axilla)
• Are pregnant; although the twinkling marker is made of material widely used in orthopedic procedures, and hence, has an excellent safety profile, the investigators want to exclude the population of pregnant patients in this phase 0 clinical trial.