Recurrent integration of domestic cat hepatitis B virus DNA near feline CCNE1 supports an oncogenic role in hepatocellular carcinoma in cats

Hepatitis B virus (HBV) is a major etiological agent of hepatocellular carcinoma (HCC) in humans, with integration of viral DNA into the host genome playing a key role in oncogenesis. Domestic cat hepadnavirus (DCHBV), a related virus, infects felines worldwide, but its oncogenic potential remains unclear. To investigate a possible association between DCHBV and feline HCC, we analyzed liver biopsies diagnosed with HCC (n=71) and lymphocytic cholangitis controls (n=88) using PCR for DCHBV DNA detection. DCHBV DNA was present in 23.9% of HCC samples and absent in controls (P < 0.001). In situ hybridization confirmed hepatocyte-specific localization of viral nucleic acids. Viral genomes from positive cases were characterized by whole-genome sequencing and phylogenetic analysis, identifying both genotype A and a divergent genotype B virus. Targeted capture and whole-genome sequencing revealed virus-host chimeric sequences in 11/16 PCR-positive HCCs, consistent with viral integration. Integration sites included regions near the promoter of feline CCNE1, a proto-oncogene and known integration hotspot in human HBV-related HCC. These findings demonstrate a significant association between DCHBV and feline HCC and provide the first evidence of DCHBV integration into the host genome, suggesting a potential role in feline hepatocarcinogenesis. The study supports the use of naturally infected cats as a model to explore hepadnavirus-induced liver cancer.