Genomic Characterization of Vulvar Squamous Cell Carcinoma To Reveal Differential Gene Expression Based on Clinical Outcome

ASCO 2023 Abstract
Authors Mary E. Gordinier, Geoffrey Schau, Shanna Brotzge Pollock, Lisa Shields, Sameer S. Talwalkar

Background:The greatest challenge in the management of vulvar squamous cell carcinoma (VSCC) is treatment of recurrent disease where options for surgery and radiation have been exhausted, or treatment of disease where distant metastasis is present. Identification of mutations differentially expressed between tumor from patients who died of aggressive disease and tumor from patients with an indolent course could reveal novel prognostic indicators and guide development of therapeutic drugs.

Methods:From 202 consecutive patients with VSCC, patients who recurred and died of disease (group A) were identified and matched by age, tumor size, depth of invasion and nodal status with those whose disease did not recur (group B). Tumor and matched normal samples from 21 patients were assayed by a broad NGS panel covering 648 genes, including whole exome and transcriptome sequencing. Immunohistochemistry (IHC) for PD-L1 (22C3) and p16 was also performed.

Results:Whole transcriptome data revealed 6 genes that were strongly differentially expressed between the aggressive and indolent groups: ACVR2A, TGM3, ROS1, NFEL2, CCND1 and BCL6. Biologically relevant DNA mutations were significantly greater in the aggressive cohort versus the indolent cohort: 7 vs 2.3 mutations per patient. The most common genomic alterations were mutations in TP53 and the promoter region of TERT. TP53 alterations occurred almost exclusively in group A. Other common genomic events include alterations of FAT1, CDKN2A, PIK3CA, CCND1, and LRP1B. All samples were MSI stable, and tumor mutational burden was similar in groups A and B. Most VSCC specimens (81%) were positive for PD-L1.

Conclusions:We report that TGM3 and ACVR2A genes are significantly under-expressed in tumors with poor outcome. Further investigation into the silencing of these genes may advance knowledge of the pathogenesis of VSCC and potentially yield therapeutic targets. Clinical outcome of VSCC appears independent of MSI, TMB or PD-L1 status.

Genes with significant differential expression.
Gene Overall, n = 21 Group A, n = 11 Group B, n = 10 p-value2
ACVR2A 2.50 (2.40, 2.64) 2.40 (2.30, 2.52) 2.63 (2.51, 2.76) 0.005
TGM3 2.10 (1.23, 2.96) 1.23 (0.84, 2.06) 2.95 (2.15, 3.06) 0.008
ROS1 1.50 (1.22, 2.22) 2.19 (1.56, 2.23) 1.25 (1.03, 1.34) 0.013
NFE2L2 3.64 (3.61, 3.73) 3.61 (3.58, 3.66) 3.71 (3.65, 3.79) 0.036
BCL6 3.36 (3.25, 3.42) 3.26 (3.17, 3.39) 3.38 (3.33, 3.44) 0.043
CCND1 3.44 (3.24, 3.83) 3.83 (3.39, 3.91) 3.37 (3.25, 3.44) 0.043

2Wilcoxon rank sum exact test.