Minimal residual disease in canine lymphoma: An objective marker to assess tumour cell burden in remission

Lymphoma is the most common haematopoietic malignancy in dogs. Since a high proportion of dogs with lymphoma achieve remission soon after initiation of chemotherapy, an objective marker assessing treatment efficacy is required. Following clinical remission, the residual population of tumour cells can be referred to as the minimal residual disease (MRD). MRD traditionally has been detected by cytology and flow cytometry; however, if the burden of malignant cells is low, these methods might not be sufficiently sensitive to detect MRD. As an extension of the development of PCR for antigen receptor gene rearrangements (PARR) in dogs, there has been recent progress in the application of real-time quantitative PCR (RT-qPCR) to canine lymphoma. With the RT-qPCR system, a very high sensitivity (1 cell per 10,000 cells) has been achieved by preparing allele-specific oligonucleotide primers and probes designed from neoplastic clones of each dog. A series of MRD diagnostics studies employing the RT-qPCR system has revealed its usefulness as a prognostic indicator, an objective marker of treatment efficacy and a predictor of relapse for dogs with lymphoma receiving chemotherapy. Introduction of the MRD monitoring system will provide an innovative scientific tool in the development of superior treatments and monitoring strategies for canine lymphoma.