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Medical Science
Personalized Medicine
Pharmacogenomics and Targeted Therapy
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Personalized medicine uses information about a person, their genes, and their disease to choose prevention, diagnosis, and treatment strategies. Pharmacogenomics is a major part of this approach because gene variants can change how a patient absorbs, breaks down, or responds to a drug. This matters because the same dose can help one patient, fail in another, or cause serious side effects in a third. By combining clinical data with genetic testing, doctors can make treatment choices that are more precise and safer.
Key Facts
- Pharmacogenomics studies how genes affect drug response.
- CYP450 enzymes help metabolize many drugs, and CYP2D6, CYP2C9, and CYP2C19 are common examples.
- Drug exposure is often estimated by AUC = total drug in blood over time.
- Warfarin dose can be influenced by variants in CYP2C9 and VKORC1.
- Targeted cancer therapy can match a drug to a tumor mutation, such as HER2-positive breast cancer treated with HER2-targeted drugs.
- Genotype is inherited DNA information, while phenotype is the observable trait or drug response.
Vocabulary
- Personalized medicine
- Personalized medicine is medical care tailored to a patient's genes, environment, lifestyle, and disease features.
- Pharmacogenomics
- Pharmacogenomics is the study of how genetic differences affect a person's response to medicines.
- CYP450 enzymes
- CYP450 enzymes are liver proteins that chemically modify many drugs so they can be activated, inactivated, or removed from the body.
- Biomarker
- A biomarker is a measurable biological sign, such as a gene variant or protein level, that helps guide diagnosis or treatment.
- Tumor sequencing
- Tumor sequencing is the analysis of cancer cell DNA to find mutations that may guide targeted therapy.
Common Mistakes to Avoid
- Assuming one genetic test predicts response to every drug is wrong because different drugs are affected by different genes and pathways.
- Treating all CYP450 variants as harmful is wrong because some variants reduce metabolism, some increase metabolism, and some have little clinical effect.
- Using tumor sequencing results as if they are always inherited is wrong because many cancer mutations are somatic and exist only in tumor cells.
- Ignoring non-genetic factors is wrong because age, kidney function, liver function, diet, drug interactions, and adherence can also strongly affect treatment response.
Practice Questions
- 1 A standard dose of a drug is 100 mg. A patient has a genotype that reduces metabolism, so the clinician starts at 50 percent of the standard dose. What starting dose should be used?
- 2 In a clinic of 240 patients taking clopidogrel, 15 percent have a CYP2C19 variant that may reduce activation of the drug. How many patients have this variant?
- 3 A breast cancer tumor tests positive for HER2 overexpression, but the patient's normal cells do not carry a HER2 mutation. Explain why this result can still guide treatment without meaning the mutation was inherited.