Therapy for Australian cats with lymphosarcoma.

OBJECTIVE: To determine the response of Australian cats with lymphosarcoma to chemotherapy and/or surgery in relation to patient and tumour characteristics, haematological and serum biochemical values and retroviral status.

DESIGN: Prospective study of 61 client-owned cats with naturally-occurring lymphosarcoma subjected to multi-agent chemotherapy and/or surgery.

PROCEDURE: An accepted chemotherapy protocol utilising l-asparaginase, vincristine, cyclophosphamide, doxorubicin, methotrexate and prednisolone was modified and used to treat 60 cats with lymphosarcoma. Clinical findings were recorded before and during therapy. As far as practical, cases were followed to death, euthanasia or apparent cure. Owner satisfaction with the results of chemotherapy was determined using a questionnaire sent after the completion of chemotherapy.

RESULTS: One cat, with lymphosarcoma limited to a single mandibular lymph node, was treated using surgery alone and was cured. The other 60 cats were treated using multi-agent chemotherapy, although seven cats with localised intestinal, ocular and subcutaneous lesions had these lesions partially (2 intestinal lesions) or completely (2 eyes, 2 intestinal lesions and a cluster of regional lymph nodes) resected prior to starting chemotherapy. The median survival time for these 60 cats was 116 days. Of the 60 cats, 48 rapidly went into complete remission following the administration of 1-asparaginase, vincristine and prednisolone (complete remission rate 80%) and these cats had a median survival of 187 days. Three cats were censored from further analysis as their long-term survival data were uninterpretable because they died of causes unrelated to lymphosarcoma or were prematurely lost to follow-up. Twenty cats were classed as 'long-term survivors' based on survival time in excess of one year and at least 14 were 'cured' based on the absence of physical evidence of lymphosarcoma 2-years after initiating treatment. In other words, of the 48 cats that reached complete remission, in excess of 29% were 'cured'. Despite detailed analysis, few meaningful prognostic indicators based on patient or tumour characteristics were identified, although long-term survivors were more likely to be less than 4-years (P= 0.04) and to have tumours of the T-cell phenotype (P= 0.06). Excluding the one FeLV ELISA-positive cat with mediastinal LSA, 7 of 9 cats less than 4 years-of-age were long-term survivors (median survival time >1271 days). There was a strong association between achieving complete remission and long-term survival (P = 0.003). On the basis of 27 replies to a questionnaire, owners were generally very satisfied with the response to chemotherapy, irrespective of the survival time of the individual patient. Eighty five percent of owners expressed complete satisfaction with their decision to pursue chemotherapy and 70% believed their cat's health status improved during the first 2-weeks of treatment. Importantly, 78% of owners considered that chemotherapy required a very substantial time commitment on their part.

CONCLUSIONS: It was possible to cure approximately one quarter of cats with lymphosarcoma using sequential multi-agent chemotherapy and/or surgery. FeLV-negative cats younger than 4 years (typically with mediastinal lymphosarcoma) had a particularly favourable prognosis. The decision to embark on chemotherapy should be based on the results of induction chemotherapy with l-asparaginase, vincristine and prednisolone, as the response to this was a good predictor of long-term survival. Cats surviving the first 16 weeks of chemotherapy generally enjoyed robust remissions (in excess of 1 year) or were cured of their malignancy.