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

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Abstract

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 (22%) 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. (J Am Acad Dermatol 2002;46:661-6.)

Section snippets

Material and methods

We searched the pathology database of University of Michigan Hospitals for patients who underwent SLNBx and local resection of their primary MCC from January 1998 to October 2000 and identified 10 consecutive patients. Clinical histories, follow-up reports from clinic visits, and pathology reports, along with hematoxylin-eosin (H&E)-stained sections and immunoperoxidase preparations of the primary tumor and SLNBxs, were retrospectively reviewed. All 10 patients had a biopsy-proven primary MCC,

Results

Table I summarizes the clinical and histopathologic findings in our patient population. Patients ranged in age from 51 to 85 years (mean, 66 years). The primary site was on an extremity in 7 (70%) cases and the head and neck in 3 (30%) cases. All 23 SLNBxs from our 10 patients were initially considered histologically tumor-free in H&E sections (Fig 1).

. Micrometastatic MCC (arrowhead) are more cohesive than lymphocytes and display larger nuclei with finely stippled hypodense chromatin without

Discussion

The significance of SLN status in patients with MCC is unknown. However, because of the aggressive nature of metastatic MCC, lack of a clear biologic understanding of its behavior, lack of therapeutic and adjuvant trials, and lack of clear evidence-based therapeutic pathways, the desire for knowledge gained from assessment of SLN status in patients with MCC seems prudent.

Although large nodules of metastatic MCC in a lymph node are easily detected in H&E-stained sections, single cells and small

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    Reprint requests: Timothy M. Johnson, MD, University of Michigan, Department of Dermatology, 1910 Taubman Center, Ann Arbor, MI 48109-0314.

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