Abstract

PRAME immunohistochemistry (IHC) has proven itself as a helpful ancillary marker for the histopathologic diagnosis of malignant melanoma (MM). One study by Lezcano et.al. reported positive PRAME IHC in 90% of conventional subtypes of MM but in only 35% of desmoplastic melanomas (DM) in a cohort of 20 cases. We aim to expand on this number by analyzing PRAME IHC in our available DMs. Fourteen (N = 14) unique diagnoses of DM were retrieved from our database from 2011 to present, and the block with the heaviest tumor burden was stained with PRAME IHC. Any staining intensity in more than 75% of malignant melanocytes was considered positive. Clinicopathologic variables collected included age, gender, location, outcomes, Breslow depth, mitotic rate and ulceration. Average age was 76 years old, male to female ratio was 6:1, and most common site was the head and neck (7 cases, 50%), followed by trunk (5, 36%) and upper extremity (2, 14%). Median follow up was 12 months with 5 patients dead of disease after a median of 8 months post-diagnosis. PRAME IHC was negative in 6 (43%) and positive in 8 cases (57%). There was no statistically significant association between PRAME expression and mitotic rate, Breslow depth or ulceration. Although our results show a higher positivity rate than previously reported (57% vs 35%), the sensitivity of PRAME in DMs is still much lower than in conventional subtypes of melanoma and caution should be exerted when interpreting a PRAME IHC for a suspected diagnosis of DM.

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