A pilot single-case longitudinal multi-omics of canine oral melanoma characterizes endogenous mutation patterns and radiotherapy-associated responses.

Canine oral melanoma is a highly aggressive tumor with limited therapeutic options and a poor prognosis. To elucidate the molecular mechanisms underlying its progression and response to radiation therapy (RT), we performed a longitudinal multi-omics analysis incorporating whole-genome sequencing (WGS) and RNA sequencing (RNA-seq) on tumor and blood samples from a single neutered male mixed-breed canine case. WGS of pre-treatment tumor tissue revealed a predominance of endogenous mutational processes, with frequent mutations in cancer-associated genes such as NTRK3, EGFR, and ADAM17, and structural variants affecting oncogenes like MDM2 and BCL2. In contrast, mutational signatures observed in the post-RT blood sample were associated with homologous recombination and mismatch repair deficiencies, with minimal structural alterations. Transcriptomic profiling demonstrated dynamic, time-dependent gene expression changes following RT. Acute responses involved immune modulation and cytoskeletal remodeling, whereas later stages were associated with oxidative stress response, epithelial regeneration, and immune resolution pathways. Shared differentially expressed genes between tumor and blood post-RT samples suggest that peripheral blood may partially capture systemic molecular responses after RT. These findings offer preliminary insights into the molecular landscape of canine oral melanoma and provide a hypothesis-generating basis for future validation of candidate molecular markers associated with RT response.