personalized medicine

personalized medicine, field of medicine in which decisions concerning disease prevention, diagnosis, and treatment are tailored to individual patients based on information derived from genetic and genomic data. Personalized medicine centres on the concept that information about a patient’s genes and genome allows physicians to make more informed and effective decisions about a patient’s care. This idea essentially is an extension of conventional medicine, in which one strategy is applied across all patients, without tailoring to personal genetic and genomic information.

Origins

The concept of personalized medicine, although not novel at the time, materialized in the 1990s, following advances in DNA sequencing technology, including automation and increased throughput. Out of those advances came efforts such as the Human Genome Project (HGP; 1990–2003), in which sequences of more than three billion base pairs of the human genome were elucidated and made available to researchers worldwide. Likewise, the International HapMap Project (2002–10), which identified genetic variations that contribute to human disease, provided researchers with the information needed to associate gene variants with specific diseases and disorders.

Those advances cast light on phenomena in medicine that had been observed for years—for example, that certain drugs are more effective in some patients and that, in response to certain medications, some patients experience unusually severe side effects. Progress in understanding the molecular factors underlying the influence of individual genetic constitution on disease and therapeutics was greatly aided by developments in pharmacogenetics and pharmacogenomics—the study of genetic causes behind differences in how individuals respond to drugs and the study of how multiple variations within the genome affect responses to drug treatments, respectively. Using data derived from pharmacogenetics and pharmacogenomics, researchers were able to develop more objective and accurate tests for disease diagnosis and for predicting how patients would respond to therapeutic agents. In some cases, researchers found, using genetic and other molecular data to inform diagnosis and treatment, that the development or outcome of certain diseases could be modified. 

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The emergence of personalized medicine was further facilitated by developments in the area of health information technology, which entails electronic processing and storage of patient data, and in the clinical uptake of personalized medicine, particularly through translational and clinical research. Advances in those areas—especially the implementation of electronic health records (EHRs), which store data on patient history, medications, test results, and demographics—were critical to the integration of data derived from genetics and genomics research and clinical settings.

Role in disease prevention, diagnosis, and treatment

Personalized medicine is used in various ways to facilitate the prevention, diagnosis, and treatment of disease. For example, physicians can use information on family history of disease to assess a patient’s risk for a disease. In certain instances, family history can be used to determine whether a patient should undergo genetic testing and, based on that information, whether the individual would benefit from specific preventive measures. In the case of individuals with a family history of Lynch syndrome (a cause of hereditary colorectal cancer), for instance, detection of the causative mutation through genetic testing can be used to inform decisions about screening. For persons who carry the mutation, frequent and routine screening for evidence of precancerous lesions in the colon allows for early disease detection, which can be a lifesaving measure. Similarly, tests capable of detecting mutations in multiple genes at one time can assist in the early diagnosis of hereditary forms of breast cancer, ovarian cancer, and prostate cancer.

The term personalized medicine is sometimes considered to be synonymous with targeted therapy, a form of treatment centred on the use of drugs that target specific molecules involved in regulating the growth and spread of cancer. Among the first successful targeted therapies was the anticancer drug imatinib, which is tailored to patients with chronic myelogenous leukemia (CML) who carry an enzyme called BCR-ABL tyrosine kinase, a protein produced by a cytogenetic abnormality known as the Philadelphia chromosome. Imatinib blocks the proliferation of CML cells that possess the mutated kinase, effectively reversing the abnoramality’s cancerous effects. 

Another example of personalized medicine applied to therapeutics is the use of genotyping to identify variations in enzymes that alter a patient’s sensitivity to the commonly prescribed anticoagulant drug warfarin. Information about variations in warfarin-metabolizing enzymes can be used to help guide decisions about the amount of the drug that a patient needs to receive in order to achieve the desired effect.

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Technical challenges and ethical considerations

Personalized medicine faces significant challenges. For example, compared with the HGP reference sequence of the human genome, each individual person’s genome houses roughly three to five million variations. Thus, attributing disease causation or therapeutic response to a given genetic variant requires careful analysis and interpretation across multiple disciplines. Moreover, genomes vary across geographic and ethnic populations and are influenced by environmental factors; thus, an individual variation identified within a given population may have very different impacts on disease in another population, based on ethnic or geographic factors.

Technological issues also continue to challenge advances in personalized medicine. The structure of EHR data, for example, can impact its utility. Access to and analysis of genomic data in EHRs may be limited by the presentation of genomic test results as a summary that includes relevant observations but excludes raw data and by the lack of information on details such as patient lifestyle and behaviour, which are essential to the accurate interpretation of genomic information.

Various ethical issues are associated with personalized medicine. Of particular concern is that the majority of genomic studies historically have focused on populations of European descent, with significant underrepresentation of racial and ethnic minorities. This unevenness in representation can impact algorithms used to guide decisions about drug selection and dosing regimens, potentially resulting in ineffective treatment and poorer outcomes for patients whose genetic backgrounds and lifestyles differ from more thoroughly studied groups.

Other ethical issues surround privacy and security concerns, mainly involving the use of EHRs. For example, a breach in an EHR system could result in the release of personal information and health data as well as information about health care providers. Personalized medicine also carries high costs and therefore is potentially inaccessible for patients who lack health insurance and financially out of reach for less-developed countries with limited health resources.