CYP2C19 and neoplasm: CYP2C19 genotyping using tumor-derived DNA (at three sites) may introduce misclassification due to potential loss-of-heterozygosity in tumor cells53, 54.Results of chi-squared tests for Hardy-Weinberg equilibrium indicate that loss-of-heterozygosity had a minor impact on observed CYP2C19 genotypes in this study.