Abstract:

Background: Conjunctival melanocytic proliferations are diagnostically challenging, often complicated by small specimen sizes, and can be separated into three broad categories. The first group includes benign nevi and primary acquired melanosis (PAM) without atypia. The second group includes junctional melanocytic proliferations with a risk of progression to invasive melanoma (PAM with atypia). The last category is conjunctival melanoma, of which 65% of tumors arise in the setting of PAM with atypia. Preferentially expressed antigen in melanoma (PRAME) immunohistochemistry has been widely adopted to differentiate cutaneous nevi and melanoma. However, there are limited studies on its utility in the evaluation of conjunctival melanocytic proliferations with little data regarding its potential utility in stratifying PAM. Methods: 29 clinically annotated cases (1 classified as non-atypical melanocytic hyperplasia, 13 PAM without atypia, and 15 PAM with atypia) were retrospectively evaluated with PRAME/MART-1 duplex immunohistochemistry (IHC) and were assigned the commonly utilized PRAME immunoreactivity score: 0 for no staining, 1+ for 1%-25% of cells positive, 2+ for 26%-50%, 3+ for 51%-75%, and 4+ for >76%. Two conjunctival melanomas and two ordinary conjunctival nevi served as control cases. Results: Nonatypical melanocytic hyperplasia and PAM without atypia showed low PRAME expression (0-3+) in 14/14 cases (100%). PAM with atypia showed strong and diffuse PRAME expression (4+) in 13/15 cases (86.7%). The two control cases of conjunctival invasive melanoma showed diffuse PRAME expression (4+), and the two control conjunctival nevi showed low PRAME expression (0-1+). Conclusion: In our limited pilot study, PRAME IHC shows a potential to discriminate PAM without atypia from PAM with atypia. Although additional larger studies are needed, PRAME appears to be a useful adjunct in evaluating junctional melanocytic proliferations of the conjunctiva.

Financial Disclosure: No current or relevant financial relationships exist.

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Michael (Yuan Yu) Huang, MD