Merkel cell polyomavirus and p63 status in Merkel cell carcinoma by immunohistochemistry: Merkel cell polyomavirus positivity is inversely correlated with sun damage, but neither is correlated with outcome.

The aim of this study was to determine the frequency of Merkel cell polyomavirus (MPyV) and p63 positivity by immunohistochemistry in a large cohort of primary Merkel cell carcinoma (MCC) from a region with high rates of actinic damage. We also aimed to determine whether there is any relationship between these markers and histological correlates of chronic sun exposure and to identify whether these markers have prognostic significance in our population. Ninety-five cases of primary cutaneous MCC were identified and stained with immunohistochemical markers for MPyV and p63. The presence of solar elastosis and squamous dysplasia in the overlying/adjacent skin were recorded as markers of actinic damage. Follow up data were obtained from the Western Australian Cancer Registry. MPyV was detected by immunohistochemistry in 23% of cases. There was a statistically significantly lower rate of positivity in tumours associated with markers of chronic sun damage as assessed by the presence of solar elastosis and squamous dysplasia. There was no association with overall or disease specific survival. p63 positivity was detected in 17% of cases. There was no association with markers of actinic damage or with overall or disease specific survival.Our data demonstrate a significant difference in rates of immunohistochemical positivity for MPyV between MCC in sun-damaged and non-sun-damaged sites. This may go some way to explaining previously identified geographical differences. When compared with a number of studies from Europe and North America, p63 positivity is less common in our population and does not show the strong prognostic significance that has been found in these other regions.