Can GSTM1 and GSTT1 polymorphisms predict clinical outcomes of chemotherapy in gastric and colorectal cancers? A result based on the previous reports

BACKGROUND Gastric and colorectal cancers remain the major causes of cancer-related death. Although chemotherapy improves the prognosis of the patients with gastrointestinal cancers, some patients do not benefit from therapy and are exposed to the adverse effects. The polymorphisms in genes including GSTM1 and GSTT1 have been explored to predict therapeutic efficacy; however, the results were inconsistent and inconclusive. MATERIALS AND METHODS A systematic review and meta-analysis was performed by searching relevant studies about the association between the GSTM1 and GSTT1 polymorphisms and chemotherapy efficacy in gastrointestinal cancers in databases such as PubMed, EMBASE, Web of Science, Chinese National Knowledge Infrastructure, and Wanfang database up to January 10, 2016. Subgroup analyses were also performed according to ethnicity, cancer type, evaluation criteria, study type, chemotherapy type, and age. RESULTS A total of 19 articles containing 3,217 cases were finally included. Overall analysis suggested that no significance was found between overall toxicity, neurotoxicity, neutropenia, gastrointestinal toxicity, tumor response, and progression-free survival, and the polymorphisms in GSTM1 and GSTT1, while GSTM1 polymorphism associated with overall survival (OS; hazard ratio =1.213, 95% confidence interval =1.060-1.388, P=0.005). Subgroup analyses suggested that neurotoxicity was associated with GSTM1 polymorphism in the Asian population, neutropenia was associated with GSTM1 polymorphism in palliative chemotherapy and older patients (mean age >60 years), and tumor response was associated with GSTT1 polymorphism in gastric cancer and responders defined by complete and partial responses. Meanwhile, GSTM1 was associated with OS in Caucasians, Asians, those with colorectal cancer, and patients with mean age <60 years. GSTT1 polymorphism was also associated with OS in Caucasians and patients with mean age >60 years. CONCLUSION The polymorphisms in GSTM1 and GSTT1 did not associate with the chemotherapy-related toxicity in gastrointestinal cancers, while GSTT1 polymorphism associated with OS, and further well-designed, larger-scale epidemiological studies are needed to validate our results.