Taken together, these results suggest that investigating the influence of pharmacogenetic variants on sorafenib pharmacokinetics in cancer patients may be particularly complex due to the two metabolic pathways (UGT1A9 and CYP3A4), the minor frequency of polymorphisms in UGT1A9 that therefore requires a larger cohort of patients, and finally the confounding effect of the poor solubility of sorafenib in the gastrointestinal medium that may contribute to a large intra- and interindividual variability in bioavailability. The gene discussed is UGT1A9; the disease is cancer.