Background: The etiology of hemangiosarcoma remains incompletely understood. Its common occurrence in dogs suggests predisposing factors favor its development in this species. These factors could represent a constellation of heritable characteristics that promote transformation events and/or facilitate the establishment of a microenvironment that is conducive for survival of malignant blood vessel-forming cells. The hypothesis for this study was that characteristic molecular features distinguish hemangiosarcoma from non-malignant endothelial cells, and that such features are informative for the etiology of this disease.Methods: We first investigated mutations of VHL and Ras family genes that might drive hemangiosarcoma by sequencing tumor DNA and mRNA (cDNA). Protein expression was examined using immunostaining. Next, we evaluated genome-wide gene expression profiling using the Affymetrix Canine 2.0 platform as a global approach to test the hypothesis. Data were evaluated using routine bioinformatics and validation was done using quantitative real time RT-PCR.Results: Each of 10 tumor and four non-tumor samples analyzed had wild type sequences for these genes. At the genome wide level, hemangiosarcoma cells clustered separately from non-malignant endothelial cells based on a robust signature that included genes involved in inflammation, angiogenesis, adhesion, invasion, metabolism, cell cycle, signaling, and patterning. This signature did not simply reflect a cancer-associated angiogenic phenotype, as it also distinguished hemangiosarcoma from non-endothelial, moderately to highly angiogenic bone marrow-derived tumors (lymphoma, leukemia, osteosarcoma).Conclusions: The data show that inflammation and angiogenesis are important processes in the pathogenesis of vascular tumors, but a definitive ontogeny of the cells that give rise to these tumors remains to be established. The data do not yet distinguish whether functional or ontogenetic plasticity creates this phenotype, although they suggest that cells which give rise to hemangiosarcoma modulate their microenvironment to promote tumor growth and survival. We propose that the frequent occurrence of canine hemangiosarcoma in defined dog breeds, as well as its similarity to homologous tumors in humans, offers unique models to solve the dilemma of stem cell plasticity and whether angiogenic endothelial cells and hematopoietic cells originate from a single cell or from distinct progenitor cells.
Bibliographical noteFunding Information:
We would like to acknowledge Cristan Jubala, Miguel Gonzalez, Ted Shade, and Okyong Cho, for technical assistance and Michelle Ritt, Mervin Yoder, Brian Van Ness, David Largaespada, Aaron Sarver, Aric Frantz, Daisuke Ito, Karin Matchett, and Tim Hallstrom, for helpful discussions. The authors acknowledge resources provided by the Minnesota Supercomputing Institute for analysis and validation of experimental data. This work was supported by grants T32 AI007405 (BAT), T32 RR018719 (SRR), P30 CA046934 (University of Colorado Cancer Center Core Support Grant), and P30 CA077598 (Masonic Cancer Center, University of Minnesota Core Support Grant) from the National Institutes of Health of the United States Public Health Service, by grants CHF#2254 and CHF#422 from the AKC Canine Health Foundation, by grant DM06-CO002 from the National Canine Cancer Foundation, by the Starlight Fund, and by charitable donations from individuals. Agencies and individuals who supported this work had no role in study design collection, analysis, or interpretation of data, writing the manuscript, or in the decision to submit the manuscript for publication. The opinions expressed in this article are solely those of the authors and do not reflect an official position by the United States Public Health Service, the AKC Canine Health Foundation, the National Canine Cancer Foundation, or other agencies.