Cancer profiling studies have had a profound impact on our understanding of the biology of cancers in a number of ways, including providing insights into the biological heterogeneity of specific cancer types, identification of novel oncogenes and tumor suppressors, and defining pathways that interact to drive the growth of individual cancers. Several large-scale genomic studies are underway that aim to catalog all biologically significant mutational events in each cancer type, and these findings will allow researchers to understand how mutational networks function within individual tumors. The identification of molecular predictive and prognostic tools to facilitate treatment decisions is an important step for individualized patient therapy and, ultimately, in improving patient outcomes. Whereas there are still significant challenges to implementing genomic testing and targeted therapy into routine clinical practice, rapid technological advancements provide hope for overcoming these obstacles.