12/13/2010 12:05 pm ET | Updated May 25, 2011

Personalized Medicine Is Becoming a Reality

It is likely that if Jay Leno stands on a street corner and asks a passerby what is meant by the term personalized medicine, the answer would be, "That is what takes place when I see my doctor. The doctor takes a history, does a physical, makes a diagnosis and prescribes the medicine that should take care of the problems." What could be more personalized than that?

Well, actually the term personalized medicine has acquired a new definition. It refers to providing highly individualized treatments, both therapeutic and preventive, based upon the patient's particular genomic make-up, which will define their susceptibility to develop certain diseases or their response to specific treatments. This will allow physicians to give the right drug to the right patient or to outline preventive measures to help reduce the likelihood that a patient will develop a disease to which he or she is susceptible. This may sound a little like science fiction, and granted, it is fairly new, but in the past decade personalized medicine has been making steady advances with researchers and physicians, and perhaps a bigger indicator, is now influencing the business model of major drug companies.

But I'm skipping ahead. Let's first go back to where this started, to the human genome project that identified and sequenced the three billion units of DNA in the body. DNA is our body's operating system. Beyond determining physical traits like eye color and hair color, DNA determines how the body behaves on a molecular level, including which diseases or disorders it will have a predisposition for, and even how it will react to certain medications. Genetic variations can influence how long a drug may stay in a patient's body, what kind of side effects it might cause, or how potent a drug will ultimately prove to be. Personalized medicine uses an analysis of a person's genome to tailor a course of treatment and maximize the potential for a positive outcome.

Not that the common cold is easy to cure, because if it were, we might have figured it out by now, but in general, genomic medicine addresses complex diseases like cancer, heart disease and diabetes that have strong multi-gene components. Genomic-guided clinical trials are already producing positive results for patients with several kinds cancer or specific stages of cancer, heart failure, and eye diseases like macular degeneration.

Prediction and Prevention
Genomic testing is also being used to determine a patient's predisposition for a particular disease. For instance, a woman who develops breast cancer and has the BRCA2 gene has a very high risk for developing breast cancer in the remaining breast, as well as a moderate risk of developing ovarian cancer. Therefore, she could choose to have close observation with frequent mammograms, blood tumor marker tests and ultrasounds of the ovaries, or may choose to have bilateral mastectomies and, following completion of childbearing, have her ovaries removed to markedly reduce the chances of developing these malignancies. With diseases like Alzheimer's, the availability of genomic information can lead to the question, "Do I really want to know?" but especially with Alzheimer's, since early detection is proving to be the key to any kind of effective treatment, the real question becomes, "Can I afford not to know?" These are just a few ways in which personalized medicine is influencing prevention and early intervention, not to mention its potential to impact health care costs.

The first molecular diagnostic tests that had widespread clinical utility was the development of tests for estrogen and progesterone receptors in breast cancer. Those women whose tumors were positive were more likely to respond to antiestrogen drugs such as tamoxifen. Now there are a number of cancer treatments that are based upon the determination of the specific intracellular abnormalities responsible for a particular patient's cancer. Once the abnormalities are defined, then specific drugs that target that abnormality can be given (called "targeted therapies"). Two of the best examples are the use of Gleevac (imatinib) that was developed to counteract the molecular abnormality found with chronic myeloid leukemia, and Herceptin (trastuzumab), which is effective in the 20 percent of patients with breast cancer who have excessive expression of a protein that Herceptin attacks.

Predicting Less Toxic Side Effects
It has been known for some time that not every patient responds the same way when a drug is given. Indeed, in some individuals a standard drug dose may reach toxic levels, while in others the standard dose is too low. The field of pharmacogenomics uses gene testing to determine the ability of a patient to respond to or metabolize medications. For instance, a test that measures this ability is the cytochrome P450 genotyping test. It looks at cytochrome enzymes that metabolize medications like antidepressants, proton pump inhibitors and anticoagulants. Because of genetic make-up, some people can't metabolize these medications fast enough so the medicine builds up, causing severe side effects. But if the medication is broken down too quickly, it doesn't get a chance to work. The P450 test can predict both adverse reaction and probable effectiveness.

More Effective Clinical Trials -- More Targeted Therapies
Personalized medicine is also changing the nature and the shape of clinical trials. Rather than a 3,000-patient study in which the data is reviewed at the end, one can select probable responders based upon the results of gene testing. This would allow the study to be carried out with a much smaller number of patients, as the trial would not be diluted with non-responders.

A New Drug Plus Its New Best Friends
Major drug companies are now developing new drugs with companion diagnostic tests, and submitting them simultaneously to the Federal Drug Administration (FDA) for approval and launch. One is a new lung cancer drug with a companion gene diagnostic test that will identify patients most likely to benefit from the drug.

The obvious question is: Do the costs of such individualized treatment make economic sense? While classic, broad stroke treatment options continue to be developed, personalized medicine takes the longer view - that genomic-guided care will save money in the long run by developing more accurate diagnostics, more effective treatments and less hardship from adverse reactions.

Putting its high-tech aspects aside, the baseline concept of personalized medicine is pretty much common sense. Everyone's been a patient at one time or another, and as a patient you know that after all the clinical trials, statistics, probabilities, and data, when you're sick, the only outcome that really matters is yours.