based on sequence homology and substrate specificity. The GSTs have well-established polymorphisms in human populations. The proteins encoded by the different alleles show different abilities to metabolize carcinogens and anticancer agents. It suggests an association between GST polymorphism and the risk for a variety of cancers as well as between said polymorphism and varying responses to cancer treatments. GSTs may also modify susceptibility in certain ethnic groups, showing ethnic dependent polymorphism.