Investigation of potential viral etiologies in the pathogenesis of feline vaccine site-associated sarcomas

The pathogenesis of feline vaccine site-associated sarcomas (VSSs) remains obscure. The low prevalence of VSSs suggests that congenital or acquired genetic factors within individual susceptible cats may act as initiators of oncogenesis. The purpose of this study was to investigate potential viral candidates in the etiopathogenesis of VSSs. Retroviruses investigated included feline immunodeficiency virus (FIV), feline foamy virus (FeFV) and endogenous feline leukemia virus (enFeLV). Vaccination could increase replication and/or expression of latent retroviruses or endogenous retroviruses within proliferating fibroblasts and/or inflammatory cells. Malignant transformation could then result from insertional activation or inactivation of cell cycle regulatory genes. DNA viruses evaluated included papillomavirus (PV), polyomavirus (PyV) and herpesvirus. Members of these three viral families have oncogenic potential and could be introduced either as vaccine contaminants or as skin contaminants transported to the subcutis by vaccination. Also, non-pathogenic or latent viruses pre-existing in host tissues could become oncogenic within the local milieu created by vaccination. Fifty formalin-fixed, paraffin-embedded VSSs were negative for the five exogenous viruses using polymerase chain reaction (PCR) and/or immunohistochemistry. The level of enFeLV RNA in VSSs was not significantly different compared to that in non vaccine site-associated feline fibrosarcomas using semi-quantitative reverse transcriptase PCR. The significance of these results is that the retroviruses FIV, FeFV and enFeLV, and the DNA viruses PV, PyV and herpesvirus do not appear to be directly involved in the etiopathogenesis of VSSs