Papillomavirus associated malignancies in dogs and cats

Papillomaviruses (PVs) infect many species of mammals and play an important role in human cancer development, and have been isolated from a number of human and animal malignancies. Here we present the preliminary findings of an investigation that is being carried out to deepen the association between papillomavirus and cancer in dogs and cats. Archive samples of 55 canine and 15 feline cutaneous and mucosal squamous cell carcinomas (SCC), and 10 canine and feline mammary carcinomas were tested with PCR to assess PV infection and immunohistochemically for p16 expression that is linked to the oncogenic activity of PV. Squamous cell carcinoma is a common malignancy in animal species, including cats, dogs, horses and sheep, which shares strict clinical and pathological similarities with human head and neck cancer. Our data strengthen the association between PV and feline SCC, as suggested by the identification of FdPV2 sequence in two cats affected by SCC in the ear pinna (6770) and neck (224/06), the latter showing strong p16 labelling. Furthermore, a feline SCC in the lip (855/02) carried PV DNA with L1 sequence 100% identical to HPV FA 16.3, supporting a possible relation between HPV types and feline SCC. In dogs, the role of PVs is well acknowledged in cutaneous and oral papillomatosis, but still controversial in SCC. In our samples, we identified PV DNA in a canine SCC (998) of the neck, whose nucleotide sequence showed 94% identity with CPV-1. As for mammary carcinomas, in two canine cases we identified a PV L1 sequence, showing 94% identity with human papillomavirus type 9 (32410, luminal B type) and 92 (40897, basal type). Our results confirm the already reported hypothetical transmission of papillomaviruses between humans and cats, and suggest that transmission may be possible also in dogs. The association between canine mammary cancer and PVs needs further confirmation. Indeed, the dog represents an increasingly powerful spontaneous animal model for the translational study of human breast cancer, in which several types of PVs seem to play a role. Further researches will be also needed to elucidate if CPV-1 may be the responsible or just an innocent by-stander in canine SCC development.