The practical application of pharmacogenetics is beginning to emerge, as researchers attempt to relate the efficacy of known treatments to genetic mutations. For example, the identification of cancer susceptibility genes offers new ways to select high-risk patients for treatment with existing chemoprevention drugs such as tamoxifen and to select patients for clinical trials of new agents.

The relative effectiveness of tamoxifen in patients with BRCA1 mutations versus those with BRCA2 mutations is an important question because tamoxifen is potentially damaging to DNA and recent data show that BRCA1 is involved in DNA repair.