Immunophenotypic and histological characterisation of 109 cases of feline lymphosarcoma

Objective To determine and analyse the immunophenotype and histological app earance of naturally occurring cases of lymphosarcoma in Australian cats. Design A prospective multi-institutional study of naturally occurring felin e lymphosarcoma. Methods One hundred and eighteen cats were referred for diagnosis and/or ma nagement of suspected lymphosarcoma. Tissue samples for histopathological a nalysis and immunophenotyping were collected as biopsies or at necropsy fro m 109 cases. Histological classification of the neoplasms followed the Work ing Formulation Classification System. Four multi-species cross-reactive an tibodies were used to classify tumours as having a B or T cell phenotype. Results Seventy-six (70%) cases were B cell tumours and 28 (26%) were T cel l tumours. The remaining 5 (4%) specimens failed to stain with the four ant ibodies. Histologically, 11 (10%) cases were classified as low-grade, 72 (6 6%) were medium-grade and 26 (24%) were high-grade tumours. There were no s ignificant associations between age and either histological grade or immuno phenotype. Mediastinal and leukaemic cases were significantly more likely t o be T cell tumours (P < 0.001 and P < 0.001, respectively). Conclusions In contrast to previously documented studies in the cat, the ma jority of cases of lymphosarcoma were of B cell phenotype and intermediate histological grade. Based on our data, the histological phenotype of lympho sarcoma is unlikely to predict immunotype, nor are cases of certain immunot ypes likely to be of specific histological subtype. Considered in relation to previous reports, the findings suggest that epidemiological factors oper ating in these cats to produce lymphosarcoma may be different to those oper ating in North American and UK cat populations.