[481] Immunohistochemical Detection of Merkel Cell Polyoma Virus in Merkel Cell Carcinoma

MP Pulitzer, AA Jungbluth, Y Chang, P Moore, KJ Busam. Memorial Sloan-Kettering Cancer Center, New York, NY; Ludwig Cancer Research Institute, New York; University of Pittsburgh, Pittsburgh

Background: A novel polyoma virus has recently been detected in Merkel cell carcinoma and found to be present in approximately 80% of tumor samples by molecular studies. A monoclonal antibody has been generated for the detection of Merkel cell polyoma virus by immunohistochemistry.
Design: Immunoperoxidase staining was performed with the novel monoclonal antibody 2B4 (produced against a predicted antigenic epitope on the Merkel cell polyomavirus encoded T antigen) using a tissue microarray of 36 Merkel cell carcinomas as well as 10 whole tumor sections, with five samples of conventional Merkel cell carcinomas and five lesions of combined cutaneous squamous cell and neuroendocrine carcinoma. Immunostaining was also performed for CK20.
Results: Using the tissue microarray samples, 27 of 36 Merkel cell carcinomas (75%) were immunoreactive for 2B4. 26 of the 27 immunopositive tumors showed positive nuclear staining in more than 75% of the tumor cells. None of the five combined neuroendocrine and squamous cell carcinomas, which were studied on sections with the entire tumor profile, and found to be CK20-positive in their invasive neuroendocrine component, showed positive immunostaining for 2B4.
Conclusions: The monoclonal antibody 2B4 permits the immunohistochemical detection of Merkel cell polyomavirus in archival material at a similar frequency as previously reported by PCR studies. Virus antigen can be detected in the majority, but not in all Merkel cell carcinomas. This observation suggests that there is some heterogeneity among tumors classified as Merkel cell carcinomas. The lack of immunoreactivity in any of the tested CK20-positive neuroendocrine carcinomas, which arose in association with a squamous cell carcinoma, suggests that the etiology and/or molecular pathway of the combined tumors is different from the majority of de novo Merkel cell carcinomas.
Category: Dermatopathology

Tuesday, March 10, 2009 9:15 AM

Platform Session: Section E, Tuesday Morning