Pharmacogenetics of breast cancer therapies.

Treatment decisions for breast cancer patients are currently based on a small number of crude predictive markers, despite the known complexity and heterogeneity of the disease. The field of pharmacogenetics can increase the precision with which therapeutic decisions are made. Discovering associations between genetic variation and treatment response will allow clinicians to tailor therapies to most effectively treat that specific tumor in that patient. In this review we outline two genes with potential clinical relevance in breast cancer treatment. A common polymorphism in the gene encoding Fc fragment of IgG low affinity IIIa receptor (FCGR3A; gene: FCGR3A) may substantially influence a patient's likelihood of responding to trastuzumab. The other gene that will be discussed in the review is cytochrome P450 2D6 (CYP2D6; gene: CYP2D6), which has many genetic variants that impair the bioactivation and effectiveness of tamoxifen therapy.