Poster Presentation Australasian Society for Dermatology Research Annual Scientific Meeting 2024

Spatial transcriptomic signatures in primary melanomas associated with sentinel node positivity. (#105)

Nicholas M Muller 1 2 , Samuel X Tan 1 2 , Chenhao Zhou 2 , Wendy Kao 2 , Nisal Vipulaguna 2 , Mitchell Stark 2 , Quan Nguyen 3 , Kiarash Khosrotehrani 1 2
  1. Dermatology, Princess Alexandra Hospital, Woolloongabba, Queensland, Australia
  2. Frazer Institute, University of Queensland, Woolloongabba, Queensland, Australia
  3. Division of Genetics and Genomics, Institute for Molecular Bioscience, The University of Queensland, St Lucia, Queensland, Australia

Introduction

Sentinel lymph node biopsy (SLNB) is an intermediate assay for locally invasive melanoma that upstages patients with occult nodal metastases for consideration of adjuvant therapy. However, SLNB is an invasive procedure that is unfortunately underperformed in the clinical setting, with only 50% of eligible patients receiving the procedure. In this study, we applied spatial transcriptomics to identify gene expression signatures in primary melanoma and evaluate the association of these features with subsequent sentinel node positivity.

 

Methods

This nested case-control series was developed within a cohort of prospectively recruited patients with new diagnoses of primary melanoma in Queensland from October 2010 to October 2014. Of 700 initial patients, we performed pairwise matching according to sentinel node positivity (case) or negativity (control), plus tumour thickness and ulceration and patient sex. For each patient, representative tumour slides were obtained from sections adjacent to the diagnostic biopsy and processed through the Visium CytAssist pipeline (10x Genomics, Pleasanton, USA). Case-control feature differences were pseudobulked and evaluated using linear modelling with precision weighting (limma-voom) for differential gene expression and the Kruskal-Wallis H test for aggregate feature scores.

 

Results

Overall, 18 patients – 9 cases and 9 controls – passed the matching criteria and had available tissue for processing. Cases demonstrated altered expression of the immune-related genes CD8A (log2fold change [logFC]: -0.784; p = 0.047) and CCL18 (logFC: +0.523, p = 0.010)  as well as an increased proportion of mast cells (controls: 0.6%; cases: 1.1%; p = 0.006) relative to controls.

 

Conclusions

Primary melanomas from patients who are SLNB-positive appear to demonstrate a chronically inflamed and immune-cold tumour micro-environment relative to tumours from SLNB-negative patients. Though these findings require validation, they may assist in prognostic classification of locally invasive melanomas, particularly for the large proportion of patients who do not receive a SLNB.