Zebrafish xenografts reveal line-specific patterns of growth, survival, and metastases in canine mammary cell lines: CMT-U27, CMT-U131, and CMT-U229.

Canine mammary tumours (CMTs) are the most common malignancies in female dogs and represent a valuable comparative model for human breast cancer. This study aimed to characterise the molecular and functional profiles of three CMT cell lines: CMT-U27, CMT-U131 and CMT-U229, using a zebrafish xenograft model. Gene ex-pression analysis targeted proliferation markers (MKI67, CCNB1, MYBL2, BIRC5, AURKA), receptor signalling (ESR1, PGR, AR, ERBB2, GRB7, EGFR), apoptosis and survival (BCL2, BAG1), and angiogenesis (VEGFA). Zebrafish larvae were xenotransplanted with tumour cells into either the Perivitelline Space or the Duct of Cuvier to assess larval survival and metastatic spread. The CMT-U27 displayed the most aggressive phenotype, with high expression of proliferation-associated genes and the highest metastatic frequency (60%). CMT-U229 exhibited moderate proliferation, accompanied by overexpression of VEGFA. In contrast, CMT-U131 exhibited lower proliferation, correlating with reduced survival in circulation and limited metastasis (<20%). This study provides the first comprehensive molecular characterisation of CMT cell lines in a zebrafish xenograft model. The findings underline the distinct biological profiles of these lines and demonstrate the utility of this platform for testing targeted therapies in veterinary oncology with translational relevance to human breast cancer.