Abstract

Merkel cell carcinoma (MCC) is a rare, aggressive cutaneous malignancy. Some immunohistochemical markers such as Ki-67 demonstrate significant prognostic value. One of the most utilized markers in MCC diagnosis is CK20 with a well-recognized perinuclear dot-like pattern. Nuclear, cytoplasmic and membranous patterns are less frequent. In this study, we sought to examine CK20 expression patterns in MCC and correlate them with clinical parameters, demographic data and prognostic potential. A retrospective analysis of 50 MCC cases was conducted. The immunohistochemical, clinicopathological and demographic variables were compiled from final diagnostic reports and patient charts. This cohort included 29 males (age 41-97) and 21 females (age 60-96). CK20 expression was positive in 49 out of 50 cases. In 47 cases, expression was described as perinuclear dot-like. 1 case was membranous, 1 case was cytoplasmic and 1 case was negative for CK20. Sun exposure was found to be a risk factor in both males (59%) and females (66.6%). Thirty cases had documented UV exposure or involvement of sun exposed areas. All 30 of the sun exposed cases showed perinuclear CK20 dot-like staining. The two cases described as membranous and cytoplasmic patterns were in individuals who responded with either complete remission or strong response to therapy despite extensive metastasis and neither had notable UV exposure. Our data shows that ultraviolet (UV) exposure likely correlates with perinuclear dot-like CK20 expression and may confer forms of MCC that are more resistant to therapy. Further studies may help elucidate relationships between CK20 expression pattern and prognostic factors.