Two patients with the same cancer receive the same drug. One responds. The other does not. Personalized medicine asks why. It tailors treatment to the individual, using genetic, molecular, and clinical information to choose the right drug at the right dose for the right patient. It is also called precision medicine.

The approach relies on biomarkers and diagnostics. A genetic test can identify a mutation that makes a tumor vulnerable to a targeted therapy. A pharmacogenomic test can predict how a patient will metabolize a drug. A liquid biopsy can monitor treatment response over time. The data guides the decision, rather than a one-size-fits-all protocol.

Personalized medicine is already changing cancer care. Herceptin for HER2-positive breast cancer, Keytruda for tumors with mismatch repair deficiency, and Tarceva for EGFR-mutant lung cancer are all examples. It is also used in rare genetic diseases, where a precise diagnosis can guide treatment. In infectious disease, it can identify the right antibiotic for a resistant infection.

The challenges are access and equity. Genomic testing is expensive, and not all patients can afford it. Data privacy is a concern. And the evidence base is still growing. Personalized medicine is not a cure-all. It is a shift toward more precise, more effective care.