Cytologic appearance of a keloidal fibrosarcoma in a dog

A 5-year-old neutered male, mixed-breed dog was presented with a single 4-mm, nodular, firm, haired subcutaneous mass on the left flank that had been present for approximately 2 weeks. Cytologic preparations of the mass revealed many spindle cells, few mast cells, rare eosinophils, rare macrophages, abundant hyalinized collagen, and moderate numbers of erythrocytes. The spindle cells were oval to fusiform, with oval nuclei, finely stippled to lacy chromatin, 1-5 variably sized prominent nucleoli, and moderate to abundant cytoplasm with indistinct cell borders, wispy cytoplasmic extensions, and occasionally, fine magenta granulation. The cell population exhibited moderate anisocytosis, moderate anisokaryosis, and rare binucleation. The eosinophilic material occurred both in large angular aggregates with blunt ends and in amorphous aggregates with fine wispy projections. Histologic findings were consistent with a keloidal fibrosarcoma. To the authors' knowledge, this report is the first to describe the cytomorphologic characteristics of a keloidal fibrosarcoma in a dog.