Lymphoma is a common hematopoietic tumour in both dogs and cats, although clinical presentation and response to treatment are different in these species. Prognostic factors are also different but generally include tumour location, histopathological grade (e.g. intermediate-high grade vs low grade) and immunophenotype.
Due to the high proliferation rate, a median survival of 4-6 weeks has been reported in untreated patients with intermediate-high grade lymphoma, while survival of only 1-2 months is achieved with palliative prednisolone treatment. Doxorubicin-based protocols (e.g. 19-week CHOP– vincristine, cyclophosphamide, doxorubicin, prednisolone) represent the standard of treatment in dogs because the highest rate of remission and longest survivals can be achieved (80-90% response, 12 months median survival, 25% survive more than 2 years).
COP protocols (vincristine, cyclophosphamide, prednisolone) or single agent doxorubicin protocols are less effective options (60-70%, 6-7 months median survival) and should be considered second line therapies. Difference in efficacy between first and second line protocols should be discussed with the owners before the option of a doxorubicin based protocol is abandoned. A 25-week CHOP protocol or COP protocols are generally used for the treatment of feline lymphoma; single agent doxorubicin is not effective in this species. Entirely oral protocols based on lomustine and prednisolone are frequently used in a rescue setting.. When remission is lost (either after an interval with no chemotherapy or after treatment at 2 or 3 week intervals), a large number of patients may experience a second remission.