Doxorubicin-based chemotherapy protocols involving cyclophosphamide, vincristine, and prednisone (CHOP), with or without L-asparaginase, are often recommended as first-line therapy for canine non-Hodgkin’s lymphoma (NHL) regardless of immunophenotype.

A retrospective study was conducted to evaluate the use of CHOP-based chemotherapy for first-line therapy of dogs with multicentric (stages III–V) T-cell lymphoma. A second objective was to evaluate prognostic factors in these patients. Dogs with T-cell lymphoma (n = 24) treated with a CHOP chemotherapy protocol were retrospectively identified. Inclusion criteria were a cytologic or histologic diagnosis of intermediate- or highgrade lymphoma, confirmed T-cell immunophenotype, intent to treat with CHOP chemotherapy, and pretreatment staging that included a complete blood count, serum biochemical profile, thoracic radiography, abdominal ultrasound, and bone marrow aspiration. The diagnosis of NHL was made on cytopathologic or histopathologic evaluation of a lymph node in all cases. Immunoreactivity with CD3 antibody and lack of reactivity with CD79a constituted a diagnosis of T-cell NHL. Dogs with gastrointestinal or skin involvement and those with suspected low-grade lymphoma were excluded. Dogs with a history of prior chemotherapy or steroid treatment were also excluded. Twenty-three of 24 dogs responded to CHOP chemotherapy and these dogs remained on the protocol for a median of 146 days. No variable was associated with progression-free survival (PFS), including stage, substage, hypercalcemia, or radiographic evidence of a cranial mediastinal mass. The median overall survival time (OST) for all dogs was 235 days. Dogs that were thrombocytopenic at presentation experienced a significantly longer OST (323 vs 212 days). The overall response rate in this population was 96%. Twenty-one of 24 (88%) had a complete response, defined as resolution of all clinically detectable disease, to CHOP chemotherapy. Two dogs were designated as having a partial response, while 1 dog had no response. These data indicate that dogs with multicentric T-cell NHL can still be well served with CHOP therapy.

Commentary: This article provides some compelling evidence that the T-cell phenotype is associated with a poor prognosis compared with the more common B-cell phenotype. Because of the shorter response durations typically seen when CHOP drugs are used to treat T-cell lymphoma, many oncologists are starting to use different drugs in place of or in combination with CHOP when treating affected dogs. One recent study evaluated L-asparaginase along with mustargen, vincristine, procarbazine, and prednisone (MOPP) as a frontline protocol for dogs with Tcell lymphoma.1 Look for future studies evaluating other drug combinations.

Given the important prognostic significance and potential treatment implications associated with T-cell lymphomas in dogs, phenotyping is more common today. The gold standard remains immunohistochemistry performed on a biopsy sample (only a small sample is needed; a trucut needle biopsy or small wedge is adequate). However, newer techniques such as PARRs (PCR for antigen receptor rearrangement) and flow cytometry are commercially available and being used more often. These tests can easily be performed in your hospital.—Dennis Bailey, DVM, Diplomate ACVIM (Oncology)

CHOP chemotherapy for the treatment of canine multicentric T-cell lymphoma. Rebhun RB, Kent MS, Borrofka SAEB, et al. VET COMP ONCOL 9:38-44, 2011.

1 Asparaginase and MOPP treatment of dogs with lymphoma. Brodsky EM, Mauldin GN, Lachowicz JL, Post GS. J Vet Intern Med 23:578-584, 2009.