Association of prostate stem cell antigen gene polymorphisms with the risk of stomach cancer in Japanese

Genetic variant in PSCA predicts survival of diffuse-type gastric cancer in a Chinese population

Recent genome-wide association study (GWAS) has identified that the prostate stem cell antigen (PSCA) rs2294008 is involving in regulating gastric epithelial-cell proliferation, influencing the risk of diffuse-type gastric cancer. We hypothesized that PSCA rs2294008 is also associated with gastric cancer survival. We genotyped PSCA rs2294008 using TaqMan method in 943 patients with surgically resected gastric cancer. Analyses of genotype association with survival outcomes were assessed by the Kaplan-Meier method, Cox proportional hazards models and the log-rank test. There was no significant association between rs2294008 and survival of gastric cancer (log-rank p=0.085 for CT/TT versus CC). However, in the stratification analysis of histology, we found that rs2294008 CT/TT genotypes were associated with significantly improved survival among diffuse-type gastric cancer (log-rank p=0.025, hazard ratio [HR]=0.75, 95% confidence interval [CI]=0.59-0.96), compared to the CC genotype. Moreover, this protective effect was more predominant for diffuse-type gastric cancer patients with tumor size >5 cm and distant metastasis. If validated in further studies, PSCA rs2294008 could be useful marker of survival assessment and individualized clinical therapy for gastric cancer, particularly among the diffuse-type gastric cancer.

Genetic variation of PSCA gene is associated with the risk of both diffuse- and intestinal-type gastric cancer in a Chinese population

Prostate stem cell antigen (PSCA), a member of the LY-6/Thy-1 family of glycosylphosphatidylinositol-anchored cell surface proteins, is considered to be involved in the cell-proliferation inhibition and/or cell-death induction activity. Two single nucleotide polymorphisms (SNPs) (rs2976392 and rs2294008) in the PSCA gene were recently identified as the susceptibility loci of gastric cancer, especially in diffuse type. Therefore, this study was to investigate whether these 2 SNPs were associated with the risk of gastric cancer in Chinese population. We genotyped rs2976392 and rs2294008 in PSCA in a case-control study including 1,053 incident gastric cancer patients and 1,100 cancer-free controls in a high-risk Chinese population. We found that variant genotypes of rs2976392 (GA/AA) were associated with a significantly 37% increased risk of gastric cancer (adjusted OR =1.37, 95% CI = 1.15-1.62), compared with variant homozygote GG, and the associations were all consistently significant in both intestinal and diffuse subtypes, and among different subgroups stratified by age, sex, drinking or smoking status. Interestingly, a significant multiplicative interaction between rs2976392 (GA/AA) and alcohol drinking was detected on the development of intestinal-type gastric cancer (p = 0.009). However, rs2294008 variant genotypes (CT/TT) were associated with a nonsignificant increased risk of gastric cancer (adjusted OR = 1.14, 95% CI = 0.96-1.36). A small meta-analysis including 5 case-control studies showed undoubtedly associations between PSCA rs2294008 and rs2976392 and gastric cancer risk (OR = 1.83, 95% CI: 1.29-2.60 and OR = 1.84, 95% CI: 1.33-2.56, respectively). These findings provide further evidence supporting that the genetic variants of PSCA gene may contribute to the gastric carcinogenesis.

Genome-wide germline analyses on cancer susceptibility and GeMDBJ database: Gastric cancer as an example

The power of an SNP-based genome-wide association study (GWAS) was first demonstrated in Japan using the JSNP database and is currently a major strategy adopted around the world for a number of common diseases including cancers. The hypothesis-free strategy can lead us to a novel hypothesis for carcinogenesis and may contribute to identifying a high risk group for research and, in the future, practice of personalized prevention. We performed a GWAS on diffuse-type gastric cancer and identified a significant association with SNPs in the PSCA (prostate stem cell antigen) gene. The association was validated by a Korean gastric case-control analysis. The PSCA protein is expressed predominantly in the stem cell/precursor-rich region of the gastric epithelium, which is considered as the origin of diffuse-type gastric cancer, and showed tumor suppressor-like characteristics. Individuals with a low PSCA promoter activity are susceptible to diffuse-type gastric cancer. By contrast, the polymorphism does not significantly predispose to intestinal-type gastric cancer, congruous to the hypothesis of the two distinct carcinogenesis pathways for the two major types of gastric cancer. In addition to publication on a specific gene, the sharing of GWAS data through a database on the web is expected to accelerate validation and discovery by other investigators. GeMDBJ (Genome Medicine Database of Japan), started in 2005 in Japan, is one of such attempts. Moreover, the advent of "next generation" sequencers may herald a new era in which the poorly explored domains of the genetic architecture of disease susceptibility may be unveiled.