Monitoring minimal residual disease in canine lymphomas treated with modified L-COP or L-CHOP protocols.

Heteroduplex polymerase chain reaction for antigen receptor rearrangements (hPARR) was developed to monitor minimal residual disease (MRD) in canine B- and T-cell lymphomas treated with the modified L-COP or L-CHOP protocol. Thirty-five dogs were recruited in this study and their neoplastic lineages were determined by immunophenotyping with Pax5 and CD3. Peripheral blood leukocytes were collected prior to and during chemotherapy in weeks 4, 9 and 13 to detect MRD by hPARR. Twenty-eight dogs (80%) had B-cell lymphoma while seven dogs (20%) had T-cell lymphoma. A monoclonal band was detected in 11 cases that showed complete or partial remission before tumour relapse and no response to the current treatment without statistical difference in clinical outcomes; however, the treatment response had an association with the MRD result (P < 0.05). Modified L-CHOP prolonged median progression-free survival as compared to modified L-COP (215 days vs. 93 days; P < 0.05). Substage b had shorter progression-free survival than substage a (90 days vs. 215 days; P < 0.05). Clinical stage III affected median overall survival time when compared to clinical stages IV and V (432, 173 and 118 days, respectively; P < 0.05). hPARR could be used for screening refractory lymphoma together with lymph node measurement in routine clinical cases.