| Gaia: | Feline injection-site sarcomas (FISSs) are malignant skin tumors of mesenchymal origin arising at local post-vaccination (or injection) sites. In recent years, a fluorescence imaging technique based on probes targeting α<sub>v</sub>β<sub>3</sub> integrin has been effectively applied for the surgical complete resection of the tumor. In our study, we investigated the utility of a commercially available anti-α<sub>v</sub> integrin polyclonal antibody for the histopathological evaluation of FISS’s surgical excision margins. We collected 10 formalin-fixed paraffin-embedded (FFPE) feline excisional biopsies with a histopathological diagnosis of FISS (7 fibrosarcomas and 3 pleomorphic sarcomas) and wide margin tissue, along with one subcutaneous injection-site granuloma and 6 osteosarcomas. Samples were processed for histology, and slides were stained for IHC with the anti-α<sub>v</sub> integrin antibody. Immunostained slides were evaluated for the cellular localization and intensity of the staining in different neoplastic and non-neoplastic cell populations. Neoplastic and non-neoplastic spindle cells had cytoplasmic positivity in all fibrosarcomas. Inflammatory cells, including macrophages of the injection-site granuloma, were negative. Multinucleated giant cells in the pleomorphic sarcomas had an intense membranous positivity. Although the anti-α<sub>v</sub> integrin antibody was ineffective for the histopathological evaluation of surgical excision margins, the membranous localization of α<sub>v</sub> integrin in multinucleated giant cells of pleomorphic sarcomas suggests that it plays a role in the oncogenesis of this FISS variant.
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