Clinical relevance of internal mammary node mapping as a guide to radiation therapy.

BACKGROUND: The surgical management of breast cancer has changed markedly with the development of lymphatic mapping and sentinel lymph node (SLN) biopsy. Lymphatic mapping technique varies with respect to injection method, mapping agent, and surgical technique. The decision to pursue the internal mammary nodes (IMN) is another source of controversy. METHODS: From April 1998 to November 2000, 1,470 patients underwent lymphatic mapping for breast cancer and were prospectively entered into the breast database. The combined technique method was used, consisting of both isosulfan blue dye and technetium-99 labeled sulfur colloid. Patients with inner quadrant lesions and suspicion for internal mammary metastasis had preoperative lymphoscintigraphy. Those with internal mammary radioactivity noted by either lymphoscintigraphy or gamma probe underwent removal of the internal mammary sentinel nodes. RESULTS: Thirty-six of the 1,470 (2.4%) patients mapped had at least 1 internal mammary lymph node removed. Inner quadrant lesions were present in 24 of the 36 (67%) IMN mapped patients. Of the 36 patients mapping to the IM area, 5 (14%) had at least 1 IM node positive. Two of the 5 (40%) had only IM metastasis, with 1 of these patients having 5 of 5 IMN positive and no disease detected in her axilla. A total of 2 of the 5 (40%) IM positive patients had more than 1 IMN positive. Twenty-eight of the 36 (78%) IM node harvested patients had preoperative lymphoscintigraphy, with 18 (64%) IMN appearing on imaging. Complications occurred in 3 of the 36 (8%) IMN mapped patients, without clinical significance. CONCLUSIONS: Mapping to the IMN basin with the finding of metastasis results in N3 disease by the current staging system. The consequence for these patients is radiation therapy to the IMN basin. It is significant to note that 14% (5 of 36) were upstaged as result of IMN detection and 40% (2 of 5) had multiple positive IMNs. Substantial disease was detected in these 5 patients necessitating additional radiation therapy while avoiding IM radiation and its attendant complications in 86% of patients mapping to the IM basin.