CLINICAL AND ANATOMICAL FEATURES OF LYMPHOSARCOMA IN 118 CATS

Objective To determine patients' characteristics and anatomical distri bution of lesions in cats with lymphosarcoma. Design Prospective multi -institutional study of naturally occurring feline lymphosarcoma. Meth ods Veterinarians in Sydney were provided with free diagnostic laborat ory services for suspect cases of feline lymphosarcoma. Lymphosarcoma was diagnosed based on physical findings, radiographic and/or ultrason ographic images and results of cytological or histopathological examin ation. When owners were not interested in pursuing an antemortem diagn osis, suspect cases were collected for necropsy Patients' characterist ics and physical findings were recorded. A modified scheme for anatomi cal classification of lesions was devised including a 'mixed' category for cases which involved two or more anatomical forms. Results One hu ndred and eighteen cases were accrued over an 18 month period. The med ian age was 120 months and range 5 to 212 months. Age distribution was bimodal, with a small peak for cats less than 24 months, and a normal distribution centred on 97 to 120 months. Eighty cats were domestic c rossbreds, 22 were Siamese or Oriental cats (including crosses), 6 wer e Burmese, 5 were purebred longhairs and the remaining 5 were one of a number of purebred shorthaired breeds. In comparison to 1017 consecut ive cases admitted to our hospital for conditions other than lymphosar coma, Siamese/Oriental cats were over-represented amongst lymphosarcom a cases (P = 0.0006). Male cats were also over-represented, accounting for 72 of 118 cases (P = 0.05). Abdominal lymphosarcoma was the most common anatomical form (43 cats), followed by mixed (39), nodal (20), mediastinal (9) and atypical (involving non-lymphoid organs, 7) forms. When analysed for specific organ involvement, 29 (25%) had mediastina l involvement, 71 (60%) had abdominal involvement including 60 (51%) w ith involvement of the intestinal tract and/or mesenteric lymph nodes and 36 (31%) with bilateral renal involvement, and 47 (40%) had periph eral lymph node involvement. No case of primary lymphoid leukaemia was identified. A noticeable subgroup of cats younger than 24 months had involvement of the anterior mediastinum with or without concurrent enl argement of cervical or axillary lymph nodes; Siamese/Oriental cats we re over-represented in this subgroup. Among cases with nodal involveme nt, lymph nodes of the head and neck were frequently involved, mandibu lar nodes most commonly, followed by superficial cervical nodes. In se ven cases a solitary node was affected. Conclusions Compared with simi lar surveys overseas, our cats were older and male cats were over-repr esented. There was a notable subgroup of young cats with mediastinal i nvolvement. Siamese/Oriental cats were over-represented in this subgro up as well as in the larger population of cats with lymphosarcoma. Com pared with overseas surveys, renal involvement, mixed cases and atypic al cases (including nasal lymphosarcoma) were more common. A new subca tegory of nodal lymphosarcoma, with involvement restricted to node(s) of head and neck, was identified.