Pharmacogenomics now has limited use in the treatment of people with cancer, but its growth may lead to the development of more tests that doctors may give patients before starting a drug therapy.

These tests are designed to analyze a patient’s genetic content to help predict whether a drug and its dosage will be safe and effective.

Many drugs that treat cancer are not fully active in the form in which they are given. They need to be “turned on,” or activated, by enzymes (proteins that speed up chemical reactions in the body) to help treat the cancer.

Each person inherits variations in these enzymes that affect how fast or slow these drugs are converted. If a person’s genes are “slow metabolizers,” or slow to break down the drug, then the body doesn’t make enough active form of the drug, and the treatment may not work as well.

Drugs also need to be “turned off,” or deactivated, after the cancer is treated to limit exposure to healthy tissues and reduce side effects. If a person’s enzymes that deactivate drugs are “slow metabolizers,” then very high levels of the unconverted drug remain in the body for a long time and can increase the side effects of the drug.

Genetic testing is already used to help predict whether some cancers are more likely to develop in people. For example, women with a variation in the BRCA1 or BRCA2 gene are at greater risk of developing breast and ovarian cancer, and men with BRCA1 and BRCA2 mutations are at increased risk of breast and prostate cancer.

The results of these genetic tests may prompt some people to have additional cancer screenings, make lifestyle changes to avoid other risk factors, and choose preventive treatment, such as chemoprevention.

Pharmacogenetic testing, however, is used for patients diagnosed with cancer and other diseases to help target the safest and most effective dose of a drug.

Pharmacogenomics offers important benefits, including:

Improving patient safety. It is estimated that severe drug reactions cause over 2 million hospitalizations each year. Pharmacogenetic testing may help identify patients who are likely to experience dangerous reactions to drugs beforehand, thereby improving patient safety and saving lives.

Improving health care costs and efficiency. The time and resources that doctors and patients spend on finding appropriate medications and doses is likely to decrease as pharmacogenetic tests are developed.

Source: CancerNet

posted October 2008

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