Absence of Merkel Cell Polyomavirus in Primary Parotid High Grade Neuroendocrine Carcinomas.
Rebecca D Chernock, Eric J Duncavage, Douglas R Gnepp, Samir K El-Mofty, James S Lewis. Washington University School of Medicine, St. Louis, MO; University of Utah, Salt Lake City; Alpert Medical School at Brown University, Providence, RI
Background: High grade neuroendocrine carcinoma of the parotid gland is a rare malignancy that may cause diagnostic confusion with metastatic neuroendocrine (Merkel cell) carcinoma of the skin, which often occurs on the head and neck, and may metastasize to parotid lymph nodes. Immunohistochemistry of these two tumors overlaps, as a subset of primary parotid gland neuroendocrine carcinomas demonstrate a “Merkel cell” immunophenotype [cytokeratin 20 (CK20) dot-like positivity]. Thus, additional diagnostic tools to differentiate these two tumor types may be clinically useful. Cutaneous Merkel cell carcinoma is known to harbor Merkel cell polyomavirus (MCPyV) in up to 80% of cases. However, the presence or absence of MCPyV in parotid neuroendocrine carcinomas has not been investigated.
Design: High grade parotid gland neuroendocrine carcinomas in patients who had no clinical evidence of primary skin Merkel cell carcinoma, lung or other neuroendocrine carcinomas were included in the study. Synaptophysin and/or chromogranin as well as CK20 immunohistochemistry results, performed as part of the original diagnostic evaluation in all cases, were recorded. The presence of MCPyV was evaluated by both immunohistochemistry (CM2B4 clone) and real-time PCR directed against the proximal large T (LT) antigen. Cases of Merkel cell carcinoma of the skin were used as positive controls.
Results: Seven cases were identified. All were either chromogranin and/or synaptophysin positive. Six of the seven cases were chromogranin positive and five were synaptophysin positive. Microscopically, five had small cell and two had large cell morphology. Four of the five small cell carcinomas (80%) were CK20 positive. One of the two large cell carcinomas (50%) was CK20 positive. All but one case had cervical lymph node metastases. MCPyV LT was not detected in any of the seven tumors, either by immunohistochemistry or PCR with adequate controls.
Conclusions: Primary parotid gland high grade neuroendocrine carcinoma, like Merkel cell carcinoma of the skin, is frequently CK20 positive. However, MCPyV LT was not detected in any of these tumors. Thus, despite similar morphologic findings these two tumors likely arise from different pathways. Furthermore, viral testing may aid in distinguishing primary tumors from metastatic Merkel cell carcinoma in the parotid gland, as a positive result would favor a metastasis.
Category: Head & Neck
Wednesday, March 2, 2011 9:30 AM
Poster Session V # 147, Wednesday Morning