DNA Methylation in Blood Samples from Malignant Mammary Tumors of Companion Dogs: A Pilot Study

Canine mammary gland tumors (cMGTs) are neoplasms arising from mammary epithelial or supporting tissues and account for approximately 50% to 70% of all tumors in intact female dogs. Epigenetic regulation, such as DNA methylation, has been investigated to elucidate the molecular mechanisms of cMGTs. This study explored whether DNA methylation alterations in peripheral blood reflect tumor-related epigenetic patterns. Eighteen client-owned dogs were enrolled, including 10 with cMGTs and 8 healthy controls. Although no individual genes reached statistical significance after multiple testing correction, exploratory gene ontology analysis identified 22 biological processes showing potential enrichment, including 2 hypermethylated and 20 hypomethylated regions. Comparative analysis between canine and human datasets revealed 91 overlapping hypomethylated genes displaying consistent patterns across both species. The top enriched gene ontology terms were morphogenesis of an epithelium and cell growth. These findings provide strictly exploratory and hypothesis-generating evidence that blood-based DNA methylation profiling may capture tumor-associated systemic epigenetic alterations in cMGTs.