Evidence of association of glutathione-S-transferase GSTT1 and GSTM1 null genotypes with susceptibility to oral cancer based on meta-analysis

The development of oral cancer results from interactions between genetic and environmental factors. GlutathioneS-transferase gene null polymorphisms have a strong impact on the detoxification of carcinogens; therefore they are expected to be related to oncogenic risk, including oral cancer. Various studies have evaluated a possible association of GSTT1 and GSTM1 null genotypes with oral cancer, including their relationship with tobacco smoking; though the findings have been inconsistent. We analyzed the available publications concerning association of tobacco smoking and GSTT1 and GSTM1 null polymorphisms and how they relate to the risk of developing oral cancer. A systematic review of the literature was conducted in the PubMed database using combinations of the following descriptors and Boolean operators `GSTM1 and GSTT1', [AND] `oral cancer', [AND] `polymorphism'. A metaanalysis of GSTT1 and GSTM1 null polymorphisms in patients with oral cancer (cases) and cancer-free individuals (controls) from each of the studies was performed. The data of each study were analyzed, and the odds ratio, the 95% confidence interval, and the number of patients were determined for each study and for all studies combined. The number of individuals analyzed was 7,839, 44.3% presenting with oral cancer and 55.7% healthy controls. The meta-analysis showed that GSTT1 and GSTM1 were associated with protection against oral cancer. A significant association of GSTT1 and GSTM1 null polymorphisms with an increased risk of developing oral cancer was observed. These findings point to a synergistic relationship between environmental and genetic factors in the development of oral cancer tumors.