CYP1A1 and carcinoma of esophagus: Although Roth et al (2000) found no significant effect of CYP1A1 exon 7 polymorphisms on either the 56 individuals with mild or moderate squamous dysplasia or the 56 control cases from a high oesophageal cancer risk region with an ethnic Chinese population, Nimura et al (1997) found subjects in China with heavy smoking habits had a three times higher frequency of the CYP1A1 Val/Val variant.