Lymphoma is the canine tumor most frequently treated with chemotherapy. It is the most common hematopoietic neoplasia of dogs ( see Canine Lymphoma Canine Lymphoma ) and cats and is also among the most responsive to chemotherapy. Four antineoplastic agents, vincristine, cyclophosphamide, doxorubicin, and prednisone, form the basis for many lymphoma treatment protocols. Treatments based on these four drugs are often abbreviated as CHOP (cyclophosphamide, hydroxydaunorubicin [doxorubicin], Oncovin® [a trade name of vincristine], and prednisone) protocols. One commonly used CHOP protocol in veterinary medicine is shown in CHOP Multidrug Chemotherapy for Treatment of Canine Lymphoma CHOP Multidrug Chemotherapy for Treatment of Canine Lymphoma 
; nearly 40 protocols for management of lymphoma in dogs have been published.
The most common recommendation in veterinary oncology is to use a discontinuous chemotherapy protocol, as opposed to maintenance or continual chemotherapy. Discontinuous chemotherapy in dogs appears to have the same or similar remission and survival duration as a traditional maintenance protocol. For this treatment approach, all chemotherapy is discontinued for patients in a complete remission at the end of the treatment protocol. At the first signs of recurrence of lymphoma, reinduction using the original chemotherapy protocol should be used. Studies have suggested that dogs receiving a discontinuous protocol were more likely to achieve a second remission when they relapsed than dogs that received longterm or maintenance chemotherapy. If reinduction fails, then use of rescue protocols should be considered.
Other lymphoma protocols include a non-doxorubicin-based combination protocol (COP) or a protocol consisting of single-agent doxorubicin administered every 3 wk. These protocols are generally well tolerated, less expensive, and easy to administer but are considered to be less effective than a CHOP-based protocol.
CHOP-based chemotherapy protocols provide the basis for most lymphoma chemotherapy protocols in cats, although there is currently no consensus treatment protocol recommended for this species. In general, fewer studies document the clinical effectiveness of various CHOP combinations in cats than in dogs.
