GSTM1 and esophageal squamous cell carcinoma: However, a pooled analysis of 11 studies could ascertain only a modest increase in risk of ESCC in GSTM1 null genotype carriers [OR = 1.197 (95% CI = 0.846–1.692)] [6], and two others failed to establish any association between GSTM1 and GSTT1 polymorphisms and risk of ESCC [28], [29].