Feline fibrosarcomas at vaccination sites and non-vaccination sites.

A retrospective study of 195 feline sarcomas diagnosed histologically between July 1988 and June 1994 showed that 170 (87.2%) were fibrosarcomas. Cats with vaccination site (VS) fibrosarcomas were younger (8.6 +/- 3.9 years; median = 8 years) than cats with non-vaccination site (NVS) fibrosarcomas (10.2 +/- 4.7 years; median = 11 years) (P = 0.03), but there was no such association with breed, sex, or "neuter status". Microscopical features more characteristic of VS fibrosarcomas than of NVS fibrosarcomas were (1) subcutaneous location (P < 0.001), (2) necrosis (P < 0.001), (3) inflammatory cell infiltration (P < 0.001), (4) increased mitotic activity (P < 0.02), (5) pleomorphism (P < 0.001), and (6) variability in the density of the extracellular matrix (P < 0.001). When these data were fitted to a logistic regression model, younger age (P = 0.003), subcutaneous location of the fibrosarcoma (P = 0.0002), and the presence of inflammation (P = 0.017) were more characteristic of VS fibrosarcomas than of NVS fibrosarcomas. The study showed that in the absence of any vaccination history, the age of a cat, coupled with certain histological characteristics (e.g., tumour location in skin, and inflammation), may help in distinguishing VS fibrosarcomas from NVS fibrosarcomas. The characteristic histological features of VS fibrosarcomas, such as necrosis, increased mitotic activity and pleomorphism, are those of aggressive tumours.