Pilot evaluation of a liquid biopsy test for longitudinal monitoring of disease status in dogs undergoing treatment for multicentric lymphoma

Canine lymphoma is a common malignancy with an annual incidence rate of 160 cases per 100,000 dogs. The primary therapeutic protocol in clinical use is treatment with cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP); however, relapses remain frequent, and early detection of recurrence is challenging. IDEXX Cancer Dx™ testing is a commercially available, blood-based test developed for the detection of canine lymphoma and may also have utility as a minimally invasive tool for longitudinal monitoring during treatment. Ten client-owned dogs with cytologic confirmation of lymphoma, immunophenotyping by flow cytometry and/or genotypic clonality testing by PCR for antigen receptor rearrangement (PARR), and an initial response to CHOP therapy were enrolled in this prospective longitudinal study. Whole blood was collected serially during chemotherapy and analyzed using Cancer Dx testing, with results reported as positive or negative. Clinical response was evaluated using the Veterinary Cooperative Oncology Group (VCOG) response evaluation criteria for peripheral nodal lymphoma in dogs. Cancer Dx test results showed concordance with clinical disease status (Somers’ D = 0.70, 95% CI [0.59, 0.82]; Kendall’s τ-b = 0.67, 95% CI [0.56, 0.78]). Among the ten cases, test results for eight (80%) dogs became negative, corresponding with clinical remission. Seven of ten (70%) dogs maintained negative test results during complete remission; five of ten (50%) dogs became positive at clinical relapse. Discordance between Cancer Dx testing results and clinical status at the time of initial clinical remission occurred in 2 out of 10 (20%) of the enrolled dogs. Two dogs (Dogs D and I) remained positive despite achieving clinical remission during the initial weeks of CHOP therapy, suggesting delayed or incomplete biomarker conversion. Serial Cancer Dx testing results were concordant with VCOG Response Evaluation Criteria-defined clinical status. While these results support further investigation of Cancer Dx testing as a monitoring tool during chemotherapy for lymphoma, the current performance of the assay is insufficient for reliable, stand-alone monitoring without further refinement.