Sporadic tumors, which account for the majority of all human cancers, evolve as the result of a step-wise accumulation of genetic alterations resulting in uncontrolled cell proliferation and a lack of response to apoptotic cues. Such genetic alterations include point mutations, deletions, duplication/amplification, and translocations and these alterations can lead to the enhanced or decreased activity of the expressed protein. These alterations are referred to as ‘gain-of-function’ or ‘loss-of-function’ mutations, respectively. The a??ected genes are termed oncogenes or tumor suppressors, respectively. Within the last decade, the availability of a complete sequence-based map of the human genome, coupled with significance technological advances, has revolutionized the search for somatic alterations in tumor genomes. Within a given tumor type there are many infrequently mutated genes and a few frequently mutated genes, resulting in incredible genetic heterogeneity. The resulting catalogues of somatic alterations will point to candidate cancer genes, but requiring further validation to determine whether they have a causal role in tumorigenesis. The availability of gene targeting and transgenic technology in the mouse gives us unparalleled opportunities to test the functional significance of genetic changes in tumor development. Another one of the broad and long-term goals of my laboratory is to develop new mouse models for human cancer. These mouse models not only will increase our understanding of genetic aberration associated with cancer progression, but also will potentially help to identify personalized medicine for cancer patients, which may eventually contribute to a decrease in morbidity and mortality of cancer.