Everyone responds differently to medicines. The dose of a drug that cures one person can be ineffective-or even toxic-in someone else. Although many non-genetic factors play a role in how an individual patient responds to a particular drug treatment, many differences in drug response come from genetic variation. Individualizing a drug's dose based on pharmacogenomic information can help a patient get the most benefit from a drug while minimizing side effects. Take the example of treating colorectal cancer with a chemotherapy regimen that includes Camptosar (irinotecan). A gene, called UGT1A1, produces an enzyme that metabolizes Camptosar. Variations in this gene can influence a patient's ability to break down the drug. About 10 percent of the North American population has a variation of the UGT1A1 gene that reduces their ability to metabolize Camptosar, leading to high blood levels of the drug and a higher risk of toxic side effects. If these patients are given standard...