The intent of this review is to present basic genetic concepts key to understanding oncogenesis and the role receptor tyrosine kinase (RTK) inhibition plays in the targeted treatment of many cancer types. Oncogenic signaling by RTKs can result from genetic events such as point mutations, chromosomal rearrangements, structural variation, and gene amplification in the cancer genome. The cancer pharmacogenes discussed encode RTKs that exemplify the link between gene variation, the oncogenic process, and the basis of targeted approaches to treatment. Biochemical pathways often involved in oncogenesis and affected by RTK variation are reviewed. Molecular diagnostic testing for the presence of specific gene variants, alterations, and amplifications direct therapy to indicated tyrosine kinase inhibitors and monoclonal antibody drugs. As pharmacists are integral to the selection, preparation, and monitoring of chemotherapy, it is important that they understand the genetic basis for targeted therapies as well as the underlying disease process.