Prevalence of NRAS Mutation, PD-L1 Expression and Amplification, and Overall Survival Analysis in 36 Primary Vaginal Melanomas

Abstract

Background: Primary vaginal melanomas are uncommon and aggressive tumors with poor prognosis, and the development of new targeted therapies is essential. This study aimed to identify the molecular markers occurring in these patients and potentially improve treatment strategies.

Materials and methods: The clinicopathological characteristics of 36 patients with primary vaginal melanomas were reviewed. Oncogenic mutations in BRAF, KIT, NRAS, GNAQ and GNA11 and the promoter region of telomerase reverse transcriptase (TERT) were investigated using the Sanger sequencing. The expression and copy number of programmed death-ligand 1 (PD-L1) were also assessed.

Results: Mutations in NRAS, KIT, and TERT promoter were identified in 13.9% (5/36), 2.9% (1/34), and 5.6% (2/36) of the primary vaginal melanomas, respectively. PD-L1 expression and amplification were observed in 27.8% (10/36) and 5.6% (2/36) of cases, respectively. PD-L1 positive expression and/or amplification was associated with older patients (p = .008). Patients who had NRAS mutations had a poorer overall survival compared with those with a wild-type NRAS (33.5 vs. 14.0 months; hazard ratio [HR], 3.09; 95% CI, 1.08-8.83). Strikingly, two patients with/without PD-L1 expression receiving immune checkpoint inhibitors had a satisfying outcome. Multivariate analysis demonstrated that >10 mitoses per mm² (HR, 2.96; 95% CI, 1.03-8.51) was an independent prognostic factor.

Conclusions: NRAS mutations and PD-L1 expression were most prevalent in our cohort of primary vaginal melanomas and can be potentially considered as therapeutic targets.

Implications for practice: This study used the Sanger sequencing, immunohistochemistry, and fluorescence in situ hybridization methods to detect common genetic mutations and PD-L1 expression and copy number in 36 primary vaginal melanomas. NRAS mutations and PD-L1 expression were the most prevalent, but KIT and TERT mutations occurred at a lower occurrence in this rare malignancy. Two patients receiving immune checkpoint inhibitors had a satisfying outcome, signifying that the PD-L1 expression and amplification can be a possible predictive marker of clinical response. This study highlights the possible prospects of biomarkers that can be used for patient selection in clinical trials involving treatments with novel targeted therapies based on these molecular aberrations.

Keywords: NRAS; Ooncogenic mutations; PD-L1 expression; Primary vaginal melanoma.

Figure 1

Photomicrographs showing immunohistochemistry staining of the programmed death‐ligand 1 (PD‐L1) expression of tumor cells and tumor‐infiltrating lymphocytes (TILs) in vaginal melanoma samples. The percentage of PD‐L1 expression in tumor cells was 0% (A), 3% (B and C), 20% (D), and 30% (E). PD‐L1‐positive staining in TILs was indicated by arrows (F).

Figure 2

The representative images of the programmed death‐ligand 1 (PD‐L1) copy number changes detected by fluorescence in situ hybridization. PD‐L1 signals with less than five copies per cell were detected in patients (A and B). Six PD‐L1 signals per cell were identified in case number 32 (C); 4.2 copies but ratio equals to 2.23 were determined in case number 28 (D); 10.7 copies and ratio equals to 2.67 were identified in case number 19 (E), whereas PD‐L1 loss was found in case number 33 (F).

Figure 3

Kaplan‐Meier curves for overall survival (OS) in the 36 investigated patients with primary vaginal melanoma. (A): Patients with wild‐type NRAS had a favorable OS than those with mutated NRAS (p = .035). (B): No statistical significance for OS between patients with/without programmed death‐ligand 1 (PD‐L1) positive staining and/or amplifications was found.