Medical oncologists have benefited greatly from relatively recent efforts to dissect and understand the genetic elements underlying mammalian cancer. The identification of specific genetic predispositions, such as mutations in BRCA-1, BRCA2, PARP-1, PARP-2, and DNA-PK, has provided key insights into the mechanisms underlying tumorigenesis and has proven useful for the design of new generations of targeted approaches for clinical intervention. For example, extreme responsiveness of tumors defective in homologous recombination because of BRCA mutations to inhibitors of PARP, a mediator of DNA repair, has recently been elucidated. With the determination of the human genome sequence and improvements in sequencing and bioinformatics technologies, systematic analyses of genetic alterations in human cancers have become possible. Clinical interventions based upon this information have, however, been severely hampered by the fact that often only a percentage of patients will respond favorably to a particular anti-cancer treatment. Medical oncologists currently cannot accurately predict which patients will or will not respond to a given anti-cancer regimen. Accordingly, there is a great need in the art to identify biomarkers which are predictive of patient responsiveness to anti-cancer therapies.