Tumor stroma is all the non-tumor recruited and host microenvironmental cells that are interacting with and exchanging information with the tumor. The focus traditionally has been on the tumor cell and all the genetic dysregulation specific to it. However, a growing body of evidence shows that these host cells both local cells within the microenvironment and those recruited from the bone marrow or distant sites to the tumor can play a crucial role in tumor growth and progression as well as response to therapy. We will measure and characterize the tumor stromal cells as well as other key host cells that may be altered in the setting of cancer and other chronic diseases. Utilizing both quantification and functional assays, including flow cytometry and colony forming unit assays, we are assessing the circulating bone marrow-derived progenitor cell populations in pediatric and adult patients with malignancies. The changes in these cells compared to patients with malignancy will be tested by assessment in changes in DNA including epigenetic changes as well as RNA including both microRNAs as well as long non-coding RNAs and proteomic approaches to demonstrate changes in protein expression. Both microRNAs and lincRNAs have been associated with developmental and tumorigenic processes and may help to explain reversible changes that occur in the host cells in response to cancer or a multitude of chronic diseases. The specific changes in these cells may help to serve as prognostic markers of disease progression as well as response to therapies. In particular, endothelial progenitor cells that are immature cells that help to form new blood vessels can be used to help predict if a given treatment is targeting angiogenesis or if it is altering the function of these cells by impairing their ability to make new blood vessels. Hematopoietic progenitor cells similarly can help to form new blood vessels and therefore also need to be measured to assess efficacy of antangiogenic therapies and the two in combination may be essential to see compensation that occurs with targeting one pathway and expansion of another. The hematopoietic progenitor cells that express vascular endothelial growth factor receptor one (VEGFR1) a receptor that is found on both endothelial and hematopoietic cells is upregulated on these cells during cancer progression and is being used as a possible marker for possible disease progression in current studies. Furthermore, clear delineation between tumor and non-tumor cells may blur as potentially recruited bone marrow-derived cells may acquire genetic mutations and in doing so become part of the growing tumor. Analysis of the genetic changes that occur in these host cells are necessary to determine if this recruitment explains the great cellular heterogeneity seen in tumors and may explain how treatment resistance arises. In addition, specific changes that occur in pro-angiogenic factors as well as these bone marrow-derived progenitor cells may be useful in elucidating changes that occur over the lifespan during growth and aging. We will perform a systematic comparison of these host bone marrow progenitor cells in the bone marrow, circulation and specific tissue sites including human pediatric tumors and metastatic or recurrent tumors as well as nearby normal tissue. Information gleamed from these studies will help us learn how to alter therapy as needed with disease progression. A more complete understanding of the pathological changes that occur within these stromal niche cells may also serve relevant to understanding the role of these cells in wound healing and in the changes that occur in development and aging. We will establish clinical trials focused on novel anti-angiogenic therapies in collaboration with several clinical consortiums including POETIC (Pediatric Oncology Experimental Therapeutic Investigation Consortium) group and COG (Clinical Oncology Group). Further, novel agents discovered in the translational studies described above that are effective in targeting the tumor stroma including those targeting specifically the VEGFR1 pathway will be taken into clinical trials for pediatric patients with malignancies. These studies can complement current traditional therapies and may prove effective in treatment of tumor progression.