Abstract:

PRAME (PReferentially expressed Antigen in MElanoma) is a melanoma-associated antigen expressed in cutaneous and ocular melanomas. Knowledge of its expression pattern across melanocytic neoplasms is still limited, and contradictory across several publications. We reviewed 1528 biopsies of melanocytic neoplasms which were clinically worked up with PRAME antibody in the period from June 2020 - May 2021. The diagnoses ranged from mildly atypical Clark’s nevi to malignant melanomas. We re-examined each biopsy and logged the percent positivity in the epidermal and dermal components. The goal of the study was to see how well PRAME positivity correlates with the diagnosis of melanoma. In the epidermal component melanomas had a median value of about 75% PRAME positivity (IQR 50%, 95%) while Clark’s nevi had a median value of 0% (IQR 0%, 5%). Still, about 5% (n=11) of all Clark’s nevi had values higher than 10% which were recognized as outliers. In the dermal component malignant melanoma had a median value of 20% PRAME positivity (IQR 0%, 72,5%) while Clark’s nevi had median of 0% (IQR 0%, 0%) in the dermal component. There were only three nevi that had higher than 10% and were recognized as outliers. When comparing MIS (melanoma in situ) to AMH (atypical melanocytic hyperplasia) we saw value in evaluation with PRAME. The median value of PRAME expression in MIS was 50% (IQR 20%, 75%) while AMH had median of 10% (IQR 0%, 20%), with only 3 lesions exhibiting positivity higher than 60% (outliers). We had 35 out of 83 malignant melanoma samples that had 0% dermal reactivity with PRAME (75% were of lentigo maligna type). Only 6 of 83 melanomas were completely PRAME negative (both epidermal and dermal components), 50% lentigo maligna type. Although this project is still ongoing, the initial data shows us that there is significant difference in PRAME reactivity, in both epidermal and dermal components, between Clark’s nevi and melanomas, and between MIS and AMH.

Financial Disclosure:
No current or relevant financial relationships exist.

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Christopher Hatcher