Technical ArticlesEstrogen Receptor Immunohistochemistry for Confirmation of Sentinel Lymph Node Metastasis in Cases With Equivocal Cytokeratin PositivityNguyen, Christopher V. MD; Deavers, Michael T. MD; Quinones, Janet HT (QIHC); Huo, Lei MD, PhD Author Information Division of Pathology and Laboratory Medicine, The University of Texas, M.D. Anderson Cancer Center, Houston, TX Reprints: Dr Lei Huo, MD, PhD, Division of Pathology, The University of Texas, M.D. Anderson Cancer Center, Unit 85, 1515 Holcombe Blvd, Houston, TX 77030 (e-mail: [email protected]). Received for publication March 13, 2008; accepted May 29, 2008 Applied Immunohistochemistry & Molecular Morphology: March 2009 - Volume 17 - Issue 2 - p 139-145 doi: 10.1097/PAI.0b013e31818192d8 Buy Metrics Abstract Differentiation of true metastases from cytokeratin (CK)-positive nonepithelial cells by immunohistochemistry occasionally may be difficult in the evaluation of sentinel lymph nodes (SLNs) for occult breast carcinoma metastases. In this study, we evaluated estrogen receptor (ER) immunostaining superimposed on CK as a method for the confirmation of metastasis when CK immunostaining alone was equivocal. We performed sequential ER staining on previously CK-stained slides on 15 axillary SLNs from breast cancer patients: 5 SLNs with known metastatic carcinoma (positive controls), 6 known negative SLNs (negative controls), and 4 test cases (3 SLNs in which CK-positive cells were equivocal for malignancy and 1 SLN in which metastasis was obvious, but contained focal weakly CK-positive signet ring cells). The primary tumor in all cases expressed ER in >50% of cells. Only 3 of 5 positive controls showed metastatic cells with dual CK/ER staining. CK-positive reticulum cells in all negative controls were ER negative. Three test cases showed dual CK/ER staining in the equivocal cells. The case with signet ring cells showed strong ER staining in the nonsignet ring cells and weaker staining in the signet ring cells. We conclude that dual CK/ER staining can be useful in SLNs when CK staining alone is equivocal, particularly when the primary tumor is known to have high expression of ER. Although dual ER/CK positivity helps to confirm metastasis, negative ER staining does not exclude metastatic disease. © 2009 Lippincott Williams & Wilkins, Inc.