Summary

Objective: Correlations between histological parameters of vaccine-associated feline fibrosarcomas and clinical follow-up data were examined retrospectively. Aim of the study was to determine histological criteria allowing a prognostical estimation of the postoperative disease-free interval and the survival time. Materials and methods: 41 cats were included in the study, all of which had developed a fibrosarcoma at typical injection sites. The tumours were surgically excised and examined histopathologically. In the first step, numerous histological criteria were examined and evaluated with a score system. Subsequently, se - veral histological criteria were combined to gain different variations of an overall score. Disease progression of each cat was closely observed over a time period of at least one year. Results: 28 of the 41 cats (68%) showed recurrence within one year of surgery, on average after 145 days (median 90 d, minimum 21 d, maximum 325 d). Cats with primary tumours showed a significantly more favorable prognosis regarding the postoperative disease-free time interval than cats initially referred with a relapsed fibrosarcoma. None of the histological criteria correlated significantly with the disease-free survival time or total survival time when criteria were assessed individually. However, an overall score made up of a combination of various histological criteria was significantly correlated to the prognosis. The extent of the infiltration of the fibrosarcomas into the periphery seems to be a critical factor. Conclusion: Fibrosarcomas commonly show recidivism. Even histopathologically less malignant appearing tumours can have an unfavorable prognosis. Clinical relevance: Grading of feline vaccine-associated fibrosarcomas only has a prognostic value if the degree of infiltration into the periphery is taken into account.