A fibrosarcoma with typical features of post-injection sarcoma was documented at the site of a microchip implant in a dog. The patient was a nine-year-old male French bulldog from Ontario, Canada and was presented for a subcutaneous mass located at the site of a microchip implant. Cytologic examination of the mass was suggestive of a malignant mesenchymal neoplasm. Histologically, the mass was confirmed as a high-grade infiltrative fibrosarcoma, with multifocal necrosis in peripheral lymphoid aggregates. By immunohistochemistry, the sample was investigated for vimention, smooth muscle actin, CD3, CD79á, and CD18. All the neoplastic cells were positive for vimentin. Scattered cells at the periphery of the lesion were also positive for smooth muscle actin, highlighting a myofibroblastic phenotype. The lymphoid cells were positive for CD18 and CD3. No aluminum deposits were detected by the aurintricarboxylic acid method. A diagnosis of fibrosarcoma morphologically similar to feline post injection sarcomas was made. Fibrosarcoma at the site of injections have been reported in dogs and ferrets. Furthermore, neoplastic growth of the site of microchip implant in the dog and laboratory rodents has been described previously.

Reference: Vascellari et al, Vet Pathol 43:545-548, 2006.