Sentinel lymph node (SLN) biopsy is thought to be a highly accurate method of assessing axillary nodal status in breast cancer. Furthermore, it can improve axillary staging by providing a more detailed examination of selected lymph nodes with a high probability of metastasis rather than the entire axillary nodes. The purpose of this study was to assess the incidence of SLN micrometastasis in node-negative breast cancer.

SLN biopsy was performed in 40 patients with clinically node-negative breast cancer using vital blue dye and/or radioisotope methods; the blue dye method was used in 21 cases, the isotope method in 14 cases, and a combination of both methods in 5 cases. All lymph nodes were evaluated by routine pathologic examination, and a more detailed examination was performed on sentinel nodes in node-negative cases; sentinel nodes were serially sectioned at an interval of 40µm depth followed by H&E and cytokeratin immunohistochemical (IHC) staining.

Sentinel nodes were detected in 35 of 40 patients (87.5%). The mapping technique used in the remaining 5 cases was vital blue dye method only. Axillary node metastasis was found in 16 of 40 patients. Sentinel node biopsy accurately reflected the axillary node status in all cases; the sensitivity, specificity, and overall accuracy were 100, 100 and 100%, respectively. In 11 of 16 node-positive patients (68.8%), sentinel nodes were the only metastatic nodes. Occult micrometastases were found in SLN by serial section and IHC staining in 4 of 19 patients diagnosed as nodenegative by routine pathological examination (21.1%). Occult micrometastasis of SLN was not correlated with primary tumor size, histologic grade or Iymphovascular invasion with the exception of the S-phase fraction (P=0.023).

SLN biopsy was a highly accurate method of assessing axillary node metastasis in breast cancer. Serial sectioning and IHC staining of SLN were sensitive methods in the detection of occult lymph node metastasis.