Pharmacogenetics in cancer etiology and chemotherapy.

Introduction Drugs and other xenobiotics have effects that may vary greatly among individuals. Such variability in effect may be due to variability in either pharmacokinetics or pharmacodynamics. The major determinant of variability in pharmacokinetics is drug metabolism, which in many cases is due to polymorphisms in the genes for drug-metabolizing enzymes (1). This often results in subpopulations of poor metabolizers of a particular drug due to a genetically determined deficiency of the drugmetabolizing enzyme. The majority of individuals, by contrast, may be classified as normal or extensive metabolizers. Pharmacodynamic polymorphisms are much less common but may be increasingly identified as important determinants of drug effect