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What is Personalized Medicine?
Personalized medicine represents a new paradigm for medicine that is based on an understanding of the normal human genome as it was defined by the recently completed Human Genome Sequencing Project www.genomics.energy.gov . The gene-based knowledge and the biotechnology tools that were the result of this important project are becoming increasingly available to cancer patients and their physicians through clinical laboratory genetic testing of the tumor genome. Although most cancer diagnoses are initially organ-based, meaning that the patient is told that he or she has for example “breast cancer” or “prostate cancer” or leukemia, more recently it has been shown that specific characteristics of a patient’s cancer genome can have profound effects on response to treatment and prognosis.
Physicians can now incorporate knowledge about the tumor genome into a plan for the patient that is appropriate for their particular cancer. This allows physicians to be proactive and make personalized medicine-driven healthcare decisions instead of choosing treatments based on “one size fits all” conclusions drawn from large studies and clinical trials. While it is very important for physicians to practice evidence based medicine, the findings of large studies do not always apply to or benefit individual patients. However, it is only recently that laboratory methods have become clinically available to analyze the molecular profile of a patient’s cancer so that it can be used for treatment planning. For this reason, personalized medicine is a new approach to cancer care that is just beginning to be recognized by physicians and patients.
How is personalized cancer care delivered to patients?
Once a cancer diagnosis has been made, the next step is usually treatment planning. It is at this stage that a personalized analysis of the tumor genome can be made through genetic testing of the tumor. Pathologists have known for many years that tumor cells from two different patients with the same form of cancer may look virtually identical under the microscope, and yet the two patients can have very different disease outcomes. These differences in tumor behavior reflect the basic biology of the malignant genome which can be visualized by scanning the tumor genome for prognostic and predictive markers using genetic testing methods. These tests can be ordered by the patient’s oncologist or the diagnostic pathologist and ideally should be incorporated into a single patient evaluation that includes the diagnosis, identification of prognostic markers and presence of potential therapeutic targets.
What forms of cancer benefit from a personalized medicine approach?
Obtaining a complete tumor genome profile is potentially beneficial in any form of cancer. However, the tumor genome patterns of some types of cancer are better understood than others and for these types of cancer, physicians are better able to use genetic testing results to plan therapy. For example, at least four subtypes of breast cancer can be identified at the genomic level, each with a very different prognosis and response to therapy. Patients diagnosed with Luminal A breast cancer have an extremely favorable prognosis and may not need adjuvant chemotherapy. Alternatively, patients diagnosed with HER2 positive breast cancer have amplification of the HER2 gene in the tumor genome, which is an unfavorable prognostic marker which also represents a therapeutic target. Many of these patients will show a good response to a targeted therapy with the drug Herceptin.
Another examples of cancer that benefits from a personalized medicine approach is chronic lymphocytic leukemia (CLL). CLL is often treated with a “watch and wait” approach and many patients live many years with the disease before ever showing symptoms. On the other hand, some patients diagnosed with CLL develop aggressive symptomatic disease within a few months. Physicians can now use CLL tumor genome prognostic markers to distinguish indolent forms of the disease from those that will be aggressive.
References
www.PersonalizedMedicineCoalition.org
