Immunostaining for cytokeratin 20 improves detection of micrometastatic Merkel cell carcinoma in sentinel lymph nodes

Background: Sentinel lymph node biopsy (SLNBx) can identify Merkel cell carcinoma (MCC) micrometastasis. Objective: We attempted to examine the effectiveness of immunostaining and identify antibodies most appropriate for evaluation of SLNBxs for MCC. Methods. Histopathologic material from 10 patients with MCC who had SLNBx was reviewed. Results: Twenty-three SLNBxs from 10 patients appeared tumor-free in routine hematoxylin-eosin (H&E)-stained sections. However, tumor cells were detected in immunostained sections from 5 (2216) of 23 SLNBxs in 4 (40%) of 10 patients. Immunostains with pancytokeratin (panCK), cytokeratin-20 (CK-20), neurofilament protein, and chromogranin A were used for all primary and SLNBx specimens. All 5 (100%) micrometastatic foci stained strongly for CK-20 and panCK. Background normal lymph node tissue also stained for panCK but not for CK-20. Conclusion: Examination of H&E sections alone is insufficient for excluding micrometastatic MCC in sentinel lymph nodes, We observed the greatest sensitivity and specificity with anti-CK-20 antibody in identifying micrometastatic MCC in sentinel lymph nodes.