# Multi-modal omics analysis of a paediatric melanoma highlights mechanisms underlying treatment resistance

## TL;DR

This study analyzed a rare and aggressive melanoma in a young child to uncover molecular changes that caused rapid cancer progression and treatment resistance.

## Contribution

The study reveals spatially variable molecular features in pediatric melanoma that may drive treatment resistance and rapid progression.

## Key findings

- The tumor showed high genetic and transcriptomic diversity with increased MITF and BRAF gene copies.
- VEGFA and WNT signaling pathways were activated, along with abnormal immune therapy-related gene activity.
- Spatial variation in molecular features suggests complex tumor heterogeneity contributing to treatment failure.

## Abstract

Cutaneous malignant melanoma is a common cancer in adults but extremely rare in young children, affecting fewer than one child per million each year in Europe. Because of its rarity, most treatments for children are adapted from adult therapies, despite possible biological differences. This study aimed to explore the molecular features of a rare and aggressive melanoma in a 16-month-old patient to understand disease progression and treatment resistance.

We studied the tumour and metastases of a patient with a melanoma carrying an NRAS mutation, who received chemotherapy and immune checkpoint inhibitor treatment. The patient died 10 months after diagnosis. We used DNA methylation analysis, single-nucleus RNA sequencing, and deep spatial transcriptomic profiling to examine genetic changes, gene activity, and their spatial distribution in both the primary tumour and lymph node metastases.

Here, we show that the tumour displayed high genetic and transcriptomic diversity. We identified increases in MITF and BRAF gene copies as likely key drivers of the aggressive disease, which were not detected at diagnosis. We also found activation of biological pathways, including VEGFA and WNT signalling, and abnormal activity of several genes linked to immune therapy response, with marked variation between tumour regions.

This case demonstrates that paediatric melanoma can harbour complex and spatially variable molecular changes that contribute to rapid disease progression and treatment failure. Our findings support incorporating detailed spatial transcriptional profiling into clinical assessment to better guide therapy in rare paediatric cancers.

Melanoma is a type of skin cancer that is common in adults but extremely rare in very young children. Because it is so uncommon, children are usually treated with approaches designed for adults, which may not work as well. In this case study, we investigated an aggressive case of melanoma in a 16-month-old child to understand why the cancer progressed quickly and did not respond to treatment. We examined samples from the original tumour and its spread to the lymph nodes using advanced techniques to map genetic changes and patterns of gene activity. We found specific changes in key cancer-related genes and signals that likely drove the disease and made treatment ineffective. These results highlight the importance of detailed tumour analysis to guide better treatment strategies for rare childhood cancers.

Mucha et al. analyse tumour and metastases samples from a rare and aggressive melanoma in a 16-month-old child using advanced genetic and spatial profiling. They identify key gene changes and signaling pathways that likely drive rapid disease progression and treatment resistance, highlighting the need for detailed tumour mapping in paediatric melanoma.