Sentinel node metastasis in patients with breast carcinoma accurately predicts immunohistochemically detectable nonsentinel node metastasis

Background: Sentinel lymphadenectomy is highly accurate for identifying axi llary metastasis from a primary breast carcinoma. Nonsentinel axillary lymp h nodes (NSNs) are unlikely to contain tumor cells if the axillary sentinel node (SN) is tumor free. We previously showed that the size of the primary tumor and the size of its SN metastasis predict the risk of NSN tumor invo lvement detected by hematoxylin and eosin staining. This study used immunoh istochemical staining (MC) to determine the likelihood of NSN axillary meta stasis in the presence of SN metastasis. Methods: Between 1991 and 1997, axillary lymphadenectomy was performed in 1 56 women (157 axillary basins) who had primary breast carcinoma with SN met astasis. By hematoxylin and eosin staining, we identified NSN metastasis in 55 axillae (35%). IHC was then used to re-examine all NSNs (1827 lymph nod es) from the remaining 102 axillae. The incidence of II-IC-detected NSN inv olvement was analyzed with respect to clinical and tumor characteristics, Results: By using IHC, we identified NSN metastasis in 15 (14.7%) of the 10 2 axillae. By multivariate analysis, the size of the SN metastasis (P = .00 01) and the size of the primary tumor (P = .038) were the only independent variables predicting NSN metastasis determined by using either hematoxylin and eosin staining or IHC. Only the number of SN metastases (1 vs. >1) was a significant (P = .04) predictor of MC-detected NSN metastasis. Conclusions: Use of IHC increases the likelihood of detection of NSN metast asis, and the risk of IHC-detected metastasis increases with the size of th e SN metastasis and the size of the primary tumor. If SN involvement is mic rometastatic (less than or equal to 2 mm) or detected by using IHC, tumor c ells are unlikely to be found in other axillary lymph nodes in patients wit h a small primary turner. The clinical significance of micrometastatic dise ase in lymph nodes is controversial, and a prospective randomized study is necessary to resolve this important issue.