[500] The Spectrum of Merkel Cell Polyomavirus Expression in a Variety of Cutaneous Neoplasms and in Neuroendocrine Carcinomas from Different Anatomic Sites.

Thai Yen Ly, Sylvia Pasternak, Noreen MG Walsh. Queen Elizabeth II Health Sciences Center, Halifax, NS, Canada

Background: Most Merkel cell carcinomas (MCC) display pure neuroendocrine differentiation (PMCC) while a minority show combined neuroendocrine and non-neuroendocrine elements (CMCC). The identification of Merkel cell polyomavirus (MCV) in a majority of MCCs has suggested a viral-induced oncogenesis. Recent work has shown lack of MCV expression in CMCCs in contrast to findings in PMCCs. Moreover, studies of non-MCC tumours such as pulmonary neuroendocrine tumours (NET) and cutaneous basal cell and squamous cell carcinomas (SCC) have also yielded negative results. Our objective was to further explore the prevalence of MCV expression in a variety of different tumours.
Design: We studied 120 cases of MCC (24 PMCC, 13 CMCC, 13 MCC metastases) and non-MCC tumours of cutaneous (10 benign follicular tumours, 15 SCCs, 15 melanomas) and non-cutaneous sites (15 pulmonary NET, 15 gastrointestinal NET) diagnosed at our institution between 1989 and 2010. MCV expression by immunohistochemistry (CM2B4) was evaluated in all groups. CMCCs exhibited neuroendocrine areas associated with in situ or invasive SCC, overlying actinic keratosis or intratumoural squamous differentiation. When possible, cases were age, gender and site-matched across the different study groups.
Results: In the MCC group, MCV antigen was detected in 15/24 (63%) PMCCs, 0/13 (0%) CMCCs and 7/13 (54%) MCC metastases. Complete concordance (100%) of MCV-positivity was observed between 10 cases of primary MCC and associated metastatic MCC. All 70 non-MCC tumours, including those from both immunocompetent and immunosuppressed individuals, were negative for MCV protein expression.
Conclusions: The absence of MCV protein expression in the current series of CMCCs and non-MCC tumours concurs with earlier findings and suggests an MCV-independent oncogenic pathway for these tumours. Our systematic comparison of MCV expression in primary MCC and associated metastatic MCC revealed identical frequency and pattern of MCV-positivity. The frequency of MCV detection in the current series of PMCC is comparable to that previously reported using CM2B4 immunohistochemistry and falls within the range reported by molecular methods. Notably, the identification of MCV in only a proportion of MCCs in this study and many others invokes a role for additional etiologic factors in the pathogenesis of MCC.
Category: Dermatopathology

Wednesday, March 2, 2011 1:00 PM

Poster Session VI # 101, Wednesday Afternoon


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