Support is requested for a Keystone Symposia meeting entitled Tumor Metabolism, organized by Matthew G. Vander Heiden and Karen H. Vousden. The meeting will be held in Keystone, Colorado from February 24 - March 1, 2013. Proliferating tumor cells have different metabolic requirements than most normal differentiated cells. All cells consume nutrients to generate ATP and maintain homeostasis, however cell proliferation requires additional nutrient uptake to support macromolecular synthesis needed for cell growth. How metabolic pathways are regulated to balance these needs is not well understood, but mounting evidence suggests that metabolism is actively regulated to support cell growth, and that this regulation is intimately linked with the signal transduction pathways that control cell growth and proliferation. Metabolic changes represent some of the first differences ever noted between tumors and normal tissues. Yet, only recently has it been appreciated that many genetic events associated with cancer result in signal transduction changes to promote metabolism that is conducive to growth. This has accelerated research to understand metabolism in tumors with an eye toward targeting these pathways for improved cancer therapy. Substantial progress in the field has come from laboratories with diverse expertise providing new insights about metabolism and its regulation. However, a deeper understanding of tumor metabolism requires methods to assess metabolite flux and pathway regulation that historically have not been used to study cancer biology. Recent years have seen a remarkable advance in techniques available to interrogate metabolic pathways in vitro and in vivo. This work has been augmented by progress in modeling metabolic networks that facilitate interpretation of complex metabolism data to define key points of regulation. A growing cross talk between these systems biology approaches and traditional cancer biology studies has enabled increasingly sophisticated studies that enhance our understanding of tumor metabolism. Bringing together scientists with expertise in signal transduction, nutrient and oxygen sensing, genetic events affecting metabolism, metabolic flux measurements and network modeling will provide an opportunity to discuss the latest data informing metabolic regulation in tumors. These discussions will impact studies of metabolism in other contexts. Similarly, emerging data related to metabolic regulation in the immune systems can inform studies of tumor metabolism. PI-3 kinase is a critical regulator of metabolism and there have been numerous advances in understanding this signaling pathway; a joint meeting addressing PI-3 Kinase will enrich the dialogue across disciplines to explore how metabolism influences multiple aspects of biology.