Introduction
Ectopic accessory breast tissue can occur anywhere along the embryonic mammary line and is found in 2‑6% of the general population.(1) Though rare, cancer can arise in ectopic breast tissue, with 70-80% of these cases arising in the axillary region.(2) Once detected, ectopic breast cancer is managed under the same principles as orthotopic breast cancer. One approach involves the option of wide local excision with sentinel lymph node (SLN) biopsy followed by radiation therapy. However, SLN mapping and biopsy in axillary breast cancer can be challenging due to the proximity of the primary tumor to the axillary lymph nodes. Few studies have described the injection technique of radionuclide tracer dye in the setting of axillary breast cancer. Here, we describe a case of primary axillary breast carcinoma in which concurrent peri-tumoral and intra-tumoral injection of radionuclide tracer allowed for successful identification of SLNs. This report serves to detail the approach to SLN identification in this clinical situation and adds to the growing body of evidence documenting the feasibility of SLN mapping and biopsy in ectopic breast carcinoma.