Abstract

Background: Lentiginous melanoma has been proposed as a pattern of radial growth phase melanoma to be identified and distinguished from lentigo maligna, superficial spreading, and acral lentiginous patterns and from dysplastic nevi. There has been little discussion or debate within the literature about lentiginous melanoma, but its identity as a malignant process has been questioned. Diffuse melanocytic staining for PRAME has been recently established as a feature of malignant melanoma. We hypothesize that if lesions classified as lentiginous melanoma are radial growth phase melanomas, the neoplastic melanocytes should stain diffusely for PRAME. Methods: A retrospective study of 21 cases diagnosed as lentiginous melanomas at our institution were stained with an antibody to PRAME. Nuclear expression was scored in tumor cells as negative, 1-25% (1+), 26-50% (2+), 51-75% (3+), or 76-100% (4+). Results: All 21 cases exhibited some level of PRAME expression. 4+ expression was seen in 17 cases (17/21, 81%), 3+ expression in 3 cases (3/21, 14%), 2+ expression in 0 cases, 1+ expression in 1 case (1/21, 5%), and no cases with negative expression. A minority of cases had weak stain intensity. Conclusion: This study shows that the majority of lentiginous melanomas have a staining pattern with PRAME similar to other forms of malignant melanomas and supports inclusion of lentiginous melanomas as a form of malignant melanoma.

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