Significant associations between GSTM1/GSTT1 polymorphisms and nasopharyngeal cancer risk

Glutathione S-transferases play a critical role in the detoxification and elimination of electrophilic carcinogens by conjugating them to glutathione. Homozygous deletions of GSTM1 and GSTT1 have been suggested as risk factors for some cancers, including colorectal, pancreatic, and esophageal cancers. Results of previous individual studies published to estimate the associations between GSTM1/GSTT1 polymorphisms and nasopharyngeal cancer (NPC) risk remained controversial. Thus, we carried out a meta-analysis by pooling the odds ratios (ORs) with corresponding 95 % confidence intervals (95 % CIs) of all currently available case-control studies to shed some light on the contradictory finding. A comprehensive search of the PubMed, Embase, Web of Science, and China National Knowledge Infrastructure databases up to October 20, 2012 was performed to identify eligible studies. A total of 15 separate publications involving 2,226 NPC cases and 3,339 controls were finally included into this meta-analysis. The meta-analysis of total studies showed that the null genotypes of GSTM1 and GSTT1 were both significantly associated with increased risk of NPC (for GSTM1: OR = 1.54, 95 % CI 1.28-1.86, P OR < 0.001; for GSTT1: OR = 2.25, 95 % CI 1.50-3.36, P OR < 0.001). Subgroup analysis by ethnicity suggested that carriers of both GSTM1 and GSTT1 null genotypes in Asians were more susceptible to NPC. Additionally, in the subgroup analysis based on the sample size, significant associations of the GSTM1 and GSTT1 polymorphisms with NPC susceptibility were identified among studies both with larger case sample size (number of cases ≥ 100) and smaller case sample size (number of cases <100). Sensitivity analysis confirmed the stability of our results. These results indicate that the GSTM1 and GSTT1 polymorphisms may play crucial roles in the development of NPC, especially in Asians.