Studies suggest that immunohistochemistry improves rate of detecting sentinel lymph node metastases and is needed for adequate staging in invasive lobular carcinoma. Our study evaluates the use of cytokeratin immunohistochemistry in detecting sentinel lymph node metastases and its effect on staging patients with invasive lobular carcinoma. Material from 76 patients with invasive lobular carcinoma was reviewed. Cytokeratin immunostaining was performed on negative nodes, and deposits were classified as macrometastasis (>2.0 mm), micrometastasis (>0.2-2 mm), or isolated tumor cells (<or=0.2 mm). Of 76 cases, 24 (21 macro- and 3 micrometastases, 32%) were positive for metastasis and 14 (18%) for isolated tumor cells. Immunohistochemistry was needed for all cases with isolated tumor cells and 1 case of micrometastasis. Criteria to distinguish isolated tumor cells and micrometastasis need to be better defined. In our study, immunostaining changed nodal status and stage in 1 of 52 (2%) node-negative patients. Immunohistochemistry is essential to detect isolated tumor cells in sentinel lymph nodes. However, for detecting micro- or macrometastases, it does not provide any significant advantage over detailed histopathological evaluation of sentinel lymph node.