Several breeds of dog, including Retrievers, Bernese Mountain Dogs and Rottweilers, are known to present elevated risks of cancers including histiocytic sarcoma (HS), lymphoma, and hemangiosarcoma. HS may be misdiagnosed due to clinical presentation shared with these other cancers. Due to the aggressiveness of HS and its late diagnosis, there is no known effective treatment. With different prognostic and therapeutic options, an early and accurate diagnosis of cancer is important to select appropriate therapies to improve outcomes for affected dogs, while still being cost effective. There is a need for the development of biomarkers for early and precise detection of such cancers. The research team has identified tumoral DNA alterations specific to HS and will use these unique alterations to improve early diagnosis of HS and to develop more specific therapies. Moreover, the investigators have been able to detect these biomarkers, already used in their lab to discriminate HS, in the blood of affected dogs. The objectives of this study are to develop a non-invasive diagnostic blood test using genetic biomarkers to accurately diagnose HS, and to explore earlier diagnosis to improve treatment outcomes through the selection of targeted therapies.