Abstract

PRAME immunohistochemistry (IHC) is often positive in melanoma. Also, positivity in other malignancies (such as breast carcinoma or leukemia) can be seen with prognostic associations. After noticing PRAME positivity in a subset of Merkel cell carcinoma (MCC) cases, we aimed to assess PRAME expression in a larger cohort of MCCs and correlate the findings with the clinicopathologic data. After IRB approval, PRAME IHC was performed on 29 MCC and the clinicopathologic data were gathered. For PRAME positive cases, both the intensity of expression and percentage of positive tumor cells were noted. For statistical analysis, a Fisher Exact probability test was used for frequency data and a two sample t-test was used for continuous variables. Seventeen (58.6%) cases were positive for PRAME, and proportion of positive tumor cells ranged from 10 to 100%. Intensity was 1+ in 11 cases, 2+ in 5 cases, and 3+ in 1 case. No statistically significant clinical (including demographics, immune status, radiation exposure, treatment received, prognosis) or histopathologic (including solar elastosis, tumor size and depth, borders, tumor infiltrating lymphocytes, lymphovascular invasion, and mitotic rate) differences were identified between PRAME positive and PRAME negative MCC cases. PRAME positivity is seen in a significant proportion of MCC and dermatopathologists should be aware of such positivity to avoid misdiagnosing MCC as melanoma. In our cohort of cases, no statistically significant clinicopathologic differences were identified between PRAME positive and PRAME negative cases.

Financial Disclosure:
No current or relevant financial relationships exist.