[527] Merkel Cell Carcinoma (MCC) with Divergent Differentiation

B Martin, JJ Rios, E Poblet, V Kazakov, T Brenn, H Kutzner, E Calonje. St John's Institute, London, United Kingdom; Hospital Virgen de la Macarena, Sevilla, Spain; Hospital Universitario, Albacete, Spain; Charles University Medical Faculty Hospital, Pilsen, Czech Republic; Lothian University Hospitals, Edinburgh, United Kingdom; Dermatopathologie, Friedrichshafen, Germany

Background: MCC is a rare, aggressive tumor arising in sun-damaged skin of white elderly individuals. We report 14 cases of MCC with divergent differentiation, an unusual but well-documented phenomenon, to further characterise its clinico-pathological spectrum and relationship with polyomavirus (MCCPyV).
Design: 14 MCC with aberrant differentiation were retrieved from the consultation files of 4 of the authors. Clinical information was obtained from patient's notes or referring pathologists. PCR analysis for MCCPyV was performed from paraffin embedded tissue when available.
Results: 8 male and 6 females, all caucasian and with a mean age of 82.7 were included. MCC were located on the head and neck (8/14), extremities (3/14) and trunk (3/14). Follow up information was limited and only available in 11 cases. 8 patients underwent simple excision, 2 had surgery and adjuvant radiotherapy and 1 was only given palliative care. 7 patients (7/12) died of disease related causes within 1 year of diagnosis (4 of them with nodal metastasis, 1 with nodal and pulmonary metastasis and 1 with extension to the orbit) 2 died of unrelated causes after 4 and 5 years and 2 remained free of disease with follow up of 1 and 2 years respectively. All tumors showed the typical histological and immunohistochemical features of MCC with at least 1 divergent component. We found a single aberrant component in 8 cases (squamous in 7 cases and follicular in 1 case), 2 aberrant components in 5 tumors (glandular + squamous areas in 2, squamous + sarcomatous in 2, sarcomatous + rosettes in 1) and 1 case had 3 aberrant components (glandular + squamous + sarcomatous). All cases had dysplastic changes in the overlying epithelium and 8/14 showed epidermotropism PCR analysis for MCPyV was negative in all 12 cases tested, with positive controls.
Conclusions: 1) Clinical features are indistinguishable from classical MCC. 2) The most common aberrant differentiation is squamous 3) Coexistent SCC in situ and epidermotropism are more common than in classic MCC. 4) Our results suggest that MCPyV is absent in MCC with divergent differentiation. Similar findings have been reported by other groups. This fact questions the etiological role of MCPyV in this subset of MCC.
Category: Dermatopathology

Monday, March 22, 2010 1:30 PM

Platform Session: Section F, Monday Afternoon

 

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