Age and gender associations of virus positivity in Merkel cell carcinoma characterized using a novel RNA in situ hybridization assay

Purpose: Merkel cell carcinoma (MCC) is a highly aggressive neuroendocrine tumor of the skin. Merkel cell polyomavirus (MCPyV) plays an oncogenic role in the majority of MCCs. Detection of MCPyV in MCCs has diagnostic utility and prognostic potential. We investigated whether RNAscope, an RNA in situ hybridization (ISH) assay for detection of RNA transcripts in tissues, is useful for MCPyV detection. <p>Experimental Design: We applied an RNAscope probe targeting MCPyV T antigen transcripts on tissue microarrays (TMAs) and whole tissue sections encompassing 87 MCCs from 75 patients, 14 carcinomas of other types, and benign tissues. For comparison, quantitative PCR (qPCR) was performed on 57 cases of MCC from 52 patients.   </p> <p>Results: RNA-ISH demonstrated the presence of MCPyV in 37/75 (49.3%) cases. Notably, tumors from younger patients (< 73 years) had a significantly higher virus positivity than those from elderly patients (≥ 73 years) (64.9% vs. 34.2%, P =0.011). Female patients had a higher positive rate of MCPyV than male patients (66.7% vs. 39.6%, P =0.032). Data from both RNA-ISH and qPCR were available for 57 samples. Considering MCPyV qPCR as the gold standard for determining MCPyV status, RNAscope had 100% sensitivity and 100% specificity. There was a strong correlation between qPCR copy number and RNA-ISH product score (Spearman's correlation coefficient R² = 0.932, P < 0.0001).  </p> <p>Conclusions: RNA-ISH is comparably sensitive to qPCR for detection of MCPyV and allows for correlation with tissue morphology. This study also reveals a significant association between age, gender, and MCPyV positivity. 

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