The prognostic significance of minimal residual disease in the early phases of chemotherapy in dogs with high-grade B-cell lymphoma.

The prognostic significance of minimal residual disease (MRD) in the early phases of chemotherapy was examined in 36 dogs with multicentric high-grade B-cell lymphoma. Sequences of immunoglobulin heavy chain (IgH) gene fragments from lymphoma cells were amplified and used to design allele-specific primers and probes for real-time PCR. The dogs were treated with a 6-month modified version of the University of Wisconsin-Madison chemotherapy protocol (UW-25) and evaluated for the MRD level at weeks 6 and 11 of UW-25. Of the 31 dogs that remained on the protocol at week 11, 14 were found to be MRD negative (<10tumour cells/10(5) peripheral blood mononuclear cells [PBMCs]), whereas the other 17 were MRD positive (⩾10tumour cells/10(5) PBMCs). The progression-free survival of the dogs with MRD-negative status at week 11 (median, 337days) was significantly longer than that of the MRD-positive dogs at the same time point (median, 196days) (P=0.0002). These results indicate the clinical significance of MRD as a prognostic marker in the early phase of chemotherapy.