The analysis of genetic factors determining the success of cancer therapy has become a new and important field of research interest between pharmacology and molecular genetics.Pharmacogenetics is concerned with genetic diagnostics of defined inborn variants of drug metabolizing enzymes associated with adverse drug effects, whereas pharmacogenomics is using a whole genome approach in order to identify drug-gene interaction.Well characterized pharmacogenetic factors include allelic variants of the thiopurin methyltransferase gene (TPMT*2,*3A,*3B, *3C) associated with TPMT deficiency.This condition requires a reduction of dosage to 10% or less of the standard dosage of 6-mercaptopurine or azathioprine.Other examples include variants of the dihydropyrimidine dehydrogenase gene (DPD*2A) in association with a 5-fluorouracile (5-FU) therapy or a promoter expansiorn in UDP-glucuronyltransferase 1A1 gene (UGT1A1 *28),when irinotecan is administered.More recently, these data have been recognized by the FDA and other authorities by recommending to test for some of these enzymic deficiencies prior to drug therapy.Another area of research activities includes inborn genetic variants of the drug target itself.This field is being covered by pharmacogenomic methods such as whole genome expression profiling (WGEX) or genome-wide association studies (GWAS) and strongly overlaps with the analysis of acquired somatic mutations during the course of a cancer disease (i.e.KRAS, EGFR, BCR/ABL).