Background: The cytoreductive efficacy of the individual components of multidrug chemotherapy for canine lymphoma is difficult to evaluate after complete remission.
Objectives: To compare the cytoreductive efficacy of vincristine (VCR), cyclophosphamide (CPA), and doxorubicin (DXR) in dogs that received a 6-month modified version of the University of Wisconsin-Madison chemotherapy protocol (UW-25).
Animals: Twenty-nine dogs with high-grade B-cell multicentric lymphoma.
Methods: Rearranged immunoglobulin heavy chain gene fragments from lymphoma cells were amplified by polymerase chain reaction (PCR) and sequenced to prepare clone-specific primers and probes for real-time PCR. The number of lymphoma cells in peripheral blood was measured from diagnosis to week 11 of UW-25.
Results: The number of lymphoma cells after the 1st administration of VCR, CPA, and DXR in weeks 1–4 was decreased in 29/29 (100%), 15/29 (51.7%), and 26/27 (96.3%) dogs, respectively. The cytoreductive efficacy of CPA was less than that of VCR and DXR. VCR, CPA, and DXR administered in weeks 6–9 were effective in 5/26 (19.2%), 5/20 (25.0%), and 14/19 (73.7%) dogs, respectively, indicating the sustained cytoreductive efficacy of DXR. CPA nonresponders were heavier and exhibited a shorter 1st remission than CPA responders.
Conclusion and Clinical Importance: When using UW-25 for treatment of canine lymphoma, CPA was found to have less cytoreductive efficacy than VCR and DXR. Real-time PCR-based quantification of tumor cells is an objective marker of the efficacy of chemotherapeutic agents.