Abstract B003: Dogs with cancer have higher plasma exosome concentrations compared with healthy dogs in the COED (canine osteosarcoma early detection) study

Abstract Background: Osteosarcoma a common cancer in dogs that can serve as a translational model for certain aspects of human osteosarcoma. We previously developed a serum exosome gene signature in dogs with osteosarcoma capable of detecting minimal residual disease and predicting prognosis after therapy. Our goal is to continue expanding our understanding of exosomes for liquid biopsy applications in dogs with cancer, and to leverage this information in the design of liquid biopsy tests to address risk, early detection, and management of human cancer patients. For this study, we hypothesized that dogs with cancer would have higher plasma exosome concentrations compared with healthy control dogs. Methods: Plasma exosomes were enriched from 29 dogs with cancer, including 8 dogs with osteosarcoma, and 26 healthy control dogs. Exosome size and concentration in the plasma samples were characterized with nanoparticle tracking analysis. Wilcoxon rank sum tests were performed to assess differences between groups. Results: Dogs with cancer had a higher mean exosome concentration at 1.4 x 1012 (+/- 1.1 x 1012) particles/ml, compared with 5.0 x 1011 (+/- 2.7 x 1011) particles/ml in healthy control dogs (p = 0.0046). There was no difference in exosome size between dogs with cancer (mean diameter = 99.9 nm) and healthy control dogs (107.8 nm; p = 0.16) when all cancer types were included. However, exosomes enriched from healthy control samples were found to be significantly larger when compared to the exosomes enriched from the subset of cancer dogs that had osteosarcoma (mean exosome diameter = 83.9 nm; p = 0.0065). Similarly, when comparing exosome size between dogs with osteosarcoma and dogs with other cancers, plasma exosomes were larger in the dogs with other cancers (107.4 nm; p = 0.023). Conclusions: In this population, dogs with cancer have higher plasma exosome concentrations compared with healthy control dogs. Interestingly, we also found that dogs with osteosarcoma had significantly smaller exosome size than dogs with other cancers and healthy control dogs. Though the size of exosomes from dogs with osteosarcoma was found to be smaller, it is possible that the larger exosome concentration in dogs with osteosarcoma results in a similar total exosomal mass. Ongoing work includes analysis of exosomal cargo to develop a liquid biopsy test capable of assessing risk of osteosarcoma development in dogs, and applying similar methodology to determine exosomal genes associated with prognosis in pediatric osteosarcoma. The higher exosome concentrations in dogs with cancer suggests that this feature, combined with analysis of exosomal cargo, may have utility in development of a liquid biopsy cancer test in dogs. Citation Format: Kelly M. Makielski, Jaron M. Magstadt, Courtney H. Labe, Ali Khammanivong, Meagan Wojtysiak, Kyle Duval, Mitzi Lewellen, Amber Winter, Kelly Reid, Andrea Chehadeh, Michelle Buettner, Caitlin Feiock, Aaron K. Rendahl, Gary R. Cutter, Logan G. Spector, Brenda J. Weigel, Jaime F. Modiano. Dogs with cancer have higher plasma exosome concentrations compared with healthy dogs in the COED (canine osteosarcoma early detection) study [abstract]. In: Proceedings of the AACR Special Conference: Liquid Biopsy: From Discovery to Clinical Implementation; 2024 Nov 13-16; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2024;30(21_Suppl):Abstract nr B003.