C609T polymorphism of the NAD(P)H:quinone oxidoreductase I gene does not significantly affect susceptibility for esophageal adenocarcinoma.

Abstract

Dear Sir, The rapidly rising incidence of distal esophageal adenocarcinomas among Caucasian males in the Western world is vastly unexplained.1 An etiological role of a dysbalance between toxification and detoxification in the esophageal mucosa has been suspected. A significantly elevated prevalence of the C609T polymorphism of the detoxifying NAD(P)H:Quinone Oxidoreductase I gene has been observed recently in a small group of 61 esophageal adenocarcinoma patients. This study indicated that the polymorphic NQO1 allele may be nearly twice as common in tumor patients as in control individuals, which means, that the NQO1 polymorphism may be associated with a genetic disposition for the development of this tumor type.2 A link between the NQO1 C609T polymorphism and tumor disposition has been previously also indicated for various other tumor entities, e.g., renal cancer,3 urothelial cancer,3 colorectal cancer,4 cutaneous basal cell carcinoma,5 pediatric leukemia,6 gastric cancer2 and esophageal squamous cell cancer.7 By contrast, results regarding breast cancer have been negative8 and conflicting results have been published for lung cancer.9,10 NAD(P)H:quinone oxidoreductase 1 (NQO1; DT-diaphorase; EC 1.6.99.2) is a cytosolic flavoenzyme, protecting cells against oxidative damage.11 A single nucleotide polymorphism (C to T substitution at position 609 in the coding region of NQO1) induces a proline to serine change at position 187 in the amino acid sequence. Due to accelerated degradation of the protein, heterozygous carriers of the polymorphism (C/T) have a significantly reduced NQO1 activity whereas homozygous carriers (T/T) have no NQO1 enzyme activity at all. We have therefore investigated the association between the NQO1 C609T polymorphism and esophageal adenocarcinoma in consecutive series of individuals that have undergone esophagectomy without prior radioor chemotherapy between 1991– 2003 at the Technical University of Munich, which is one of the largest centers for esophageal cancer surgery in the Western world.12 All tumor patients as well as all controls were of Caucasian race. Information about patients’ age, gender, histopathological tumor characteristics as well as smoking and drinking habits were obtained from our prospectively documented Barrett’s Cancer database. Unfortunately the database did not contain data concerning alcohol and drinking habits for all patients. These data were completed reviewing the patients’ charts. Data about the healthy controls (age, medical history, smoking and drinking habits) were documented prospectively (interview during blood sampling). The interview included questions to rule out previous or current neoplastic diseases. Smokers were defined as formerly or currently smoking at least 5 cigarettes per day for at least 2 years. Alcohol drinkers were defined as formerly or currently drinking alcohol at least once daily, exceeding the occasional intake of one glass of wine or beer. Genomic DNA of 140 patients with primary resected esophageal adenocarcinomas (Barrett’s carcinomas) and from 260 healthy volunteers (subjects hospitalized for traumatic injuries but without any history of cancer) was prepared, using the same techniques as in our previously published investigation.2 PCR-based amplification of the NQO1 gene and subsequent restriction fragment length polymorphism analysis with the restriction enzyme Hinf I were also carried out as described previously.2 The genotypes in the control group (n 260) were distributed as follows: homozygous wild-type (C/C) 71.2%, heterozygous (C/T) 25.0%, homozygous polymorphic (T/T) 3.8%. The overall frequency of the polymorphic 609T allele was 16%. Genotype distribution and allele frequency of the NQO1 609T polymorphism are similar to frequencies reported in other German Caucasian control populations (Sarbia et al.2: 14%; Schulz et al.3: 13%). In the tumor group (n 140), the genotypes were 65.0% homozygous wild-type (C/C), 30.0% heterozygous (C/T) and 5.0% homozygous polymorphic (T/T). The frequency of the 609T allele was 20%. The overall frequency of the polymorphic allele in the tumor group was 0.200 compared to 0.164 in the control group, a statistically non-significant difference. Neither the genotype distribution nor the overall frequency of the polymorphic allele was statistically different between control and tumor group (Table I). The current study included the largest series of esophageal adenocarcinoma patients so far in an investigation on the role of a genetic polymorphism for tumor susceptibility. The statistical power to detect an odds ratio (OR) 2.8 in the esophageal cancer group was 87%. Although we found an increased frequency of the polymorphic NQO1 allele in the tumor group,