Cancer drug development is proceeding at a rapid pace, with drug approvals in oncology outpacing the other disease indications. With high population growth and economic development of Asian countries, access to cancer drugs becomes a paramount necessity. Approval of these drugs is dependent on establishing their safety and efficacy in populations living in these countries. Ethnic and racial differences in drug pharmacokinetics, or drug receptor sensitivities may lead to differences in drug responses between populations. These differences may be due to intrinsic or extrinsic factors, and understanding of the magnitude of these differences and their etiologies is important. One key pharmacogenetic reason for ethnic variability of drug response arises from the different allelic frequencies of polymorphic drug-metabolising enzyme genes, resulting in altered drug disposition. Using race or ethnicity as a "biomarker" for pharmacotherapeutics is fraught with issues as they are difficult to define scientifically, and are considered more social constructs. Nonetheless, studying the genetics of ethno-geographical variability of drug response will allow genetic biomarkers to be uncovered, which would greatly facilitate precision medicine, and should justify broadening the involvement and accrual of patients from global diverse populations during the early phases of drug development for an oncology drug.