Intradermal isotope injection: a highly accurate method of lymphatic mapping in breast carcinoma

The combined approach of radioactive tracer and blue-dye mapping of sentinel lymph nodes (SLN) has evolved into a safe and effective alternative to routine axillary node dissection in specific patient populations with breast carcinoma. The optimal route of injection for the isotope has not been clearly defined. To assess the intradermal route of isotope injection, we prospectively evaluated 100 patients with biopsy-proven invasive breast carcinoma with SLN biopsy followed by planned axillary node dissection.

All patients were given an intradermal injection of Tc-99m sulfur colloid and an intraparenchymal injection of blue dye. All patients underwent a complete axillary node dissection. Each sentinel node was serially sectioned and examined by immunohistochemistry.

Sentinel nodes were successfully identified in 99% of cases. Forty-six patients had axillary metastases; of these, four had falsely negative sentinel nodes (false-negative rate, 9%). The false-negative rate was 0 of 24 (0%) for T1 tumors, 2 of 18 (11%) for T2 tumors, and 2 of 4 (50%) for T3 tumors. Three of four patients with false negatives had palpable, clinically suspicious axillary nodes found intraoperatively. If these cases are excluded, the accuracy of the procedure was 100% for T1 and T2 tumors. Of the 42 positive axillae identified by SLNB (true positives), 40 were localized using the intradermal injection of radioisotope; in 13 of these cases, this was the only method that identified the true-positive node.

These data demonstrate that intradermal injection of radioactive tracer is an effective method of localizing the SLN in cases involving small breast cancers. Further investigation is warranted before this technique is adopted for use in larger breast cancers. Intraoperative examination and biopsy of any suspicious nonsentinel nodes are critical.