781 Melanoma subtypes demonstrate distinct PD-L1 expression profiles

Abstract

PD-L1 expression in the tumor immune microenvironment is recognized as both a prognostic and predictive biomarker in patients with cutaneous melanoma, a finding closely related to its adaptive (IFN-γ-mediated) mechanism of expression. Approximately 35% of cutaneous melanomas express PD-L1, however, the expression patterns, levels, and prevalence in rarer melanoma subtypes are not well described. We performed immunohistochemistry for PD-L1 and CD8 on 200 formalin-fixed paraffin-embedded specimens from patients with acral (n = 16), mucosal (n = 36), uveal (n = 103), and chronic sun-damaged (CSD) (n = 45) melanomas (24 lentigo maligna, 13Correspondence: Dr JM Taube, MD, Division of Dermatopathology, Johns Hopkins Hospital, Blalock 907, 600N. Wolfe Street, Baltimore, MD 21287, USA. jtaube1@jhmi.edu. CONFLICT OF INTEREST:The remaining authors declare no conflict of interest. HHS Public Access Author Manuscript Author ManuscriptAuthor ManuscriptAuthor Manuscript 'mixed' desmoplastic, and 8 'pure' desmoplastic melanomas). CD8+ tumor-infiltrating lymphocyte (TIL) densities were characterized as mild, moderate, or severe, and their geographic association with PD-L1 expression was evaluated. Discrete lymphoid aggregates, the presence of a spindle cell morphology, and the relationship of these features with PD-L1 expression were assessed. PD-L1 expression was observed in 31% of acral melanomas, 44% of mucosal melanomas, 10% of uveal melanomas, and 62% of CSD melanomas (P<0.0001). Compared to our previously characterized cohort of cutaneous melanomas, the proportion of PD-L1(+) tumors was lower in uveal (P = 0.0002) and higher in CSD (P = 0.0073) melanomas, while PD-L1 expression in the acral and mucosal subtypes was on par. PD-L1 expression in all subtypes correlated with a moderate-severe grade of CD8+ TIL (all, P<0.003), supporting an adaptive mechanism of expression induced during the host antitumor response. The tumor microenvironments observed in CSD melanomas segregated by whether they were the pure desmoplastic subtype, which showed lower levels of PD-L1 expression when compared to other CSD melanomas (P = 0.047). The presence of lymphoid aggregates was not associated with the level of PD-L1 expression, while PD-L1(+) cases with spindle cell morphology demonstrated higher levels of PD-L1 than those with a nested phenotype (P<0.0001). Our findings may underpin the reported clinical response rates for anti-PD-1 monotherapy, which vary by subtype.Increased objective response rates (ORRs) to anti-PD-1/PD-L1 monotherapy as well as improved progression-free survival and overall survival have been linked to PD-L1 expression in the tumor microenvironment (TME) in some studies. [1][2][3][4] Studies from our group and others indicate that the major mechanism driving melanoma tumor cell PD-L1 expression is an association with tumor-infiltrating lymphocytes (TIL), consistent with an endogenous antitumor immune response that may be unleashed with anti-PD-1/PD-L1 therapies. 5 Such adaptive PD-L1 expression by melanoma is...