The relationship between the ABO blood group system and the incidence of tumor has been noticed for many years. Recently, Iodice et al.
reported that the incidence risk of pancreatic cancer in blood group O individuals was significantly reduced compared with that in non-O group (RR = 0.79, 95% CI 0.70–0.90) in Europeans [19
]. Meanwhile, they investigated the relationship between ABO blood groups and other kinds of cancer, but failed to confirm the relationship between ABO blood groups and gastric cancer. In our case-control study, we found a significant relationship between ABO blood groups and gastric cancer. The risk of gastric cancer in blood groups A was significantly higher than that in non-A groups.
A systematic meta-analysis helps researchers to summarize studies on specific topics. Since meta-analysis is a combination of multiple studies, it is less influenced by separate findings from a single study. In addition, meta-analyses reveal higher statistical power than traditional single studies. Regarding the effect of ABO blood groups on the risk of gastric cancer, we performed a meta-analysis combined with our case-control study from a large cohort. The meta-analysis indicated that the risk of gastric cancer in blood group A individuals was significantly higher than that in non-A group individuals (OR = 1.11, 95% CI 1.07–1.15), whereas the individuals with blood group O showed a significantly reduced risk of gastric cancer, compared with the non-O individuals (OR = 0.91, 95% CI 0.89–0.94). Odds ratios are commonly reported in the medical literature as the measure of association between exposure and outcome [20
]. In this present study, the OR values of the relationship between blood group A and gastric cancer was in the range of 1.1–1.5, suggesting a weak association. The OR value of the relationship between blood group O and gastric cancer is in the range of 0.8–0.9, which also suggests a weak association. However, our meta-analysis failed to prove any relationship between blood group B or blood group AB with the gastric cancer risk. Regarding the heterogeneity of the publication language, data quality and data source, there are some limitations in meta-analysis. Therefore, the researchers need to search more articles including English articles and non-English articles in order to make their meta-analysis more reliable for guiding clinical work.
The association between blood group A and gastric cancer has been mentioned in the studies of several groups [9
]. In regards to the possible explanations for the increased incidence of gastric cancer in blood group A individuals, Roberts et al.
proposed that individuals with blood group A were more susceptible to pernicious anemia, compared with non-A blood group individuals [21
]. A pernicious anemia individual is more prone to gastric cancer [18
]. A clinical study demonstrated that altered gastric secretary function may be related to the ABO blood group. Compared to individuals with blood group A, the individuals of blood group O produced more free acid in their stomachs. The mean value of plasma pepsinogen in individuals with blood group O (564 units/mL) was higher than that in individuals with blood group A (494 units/mL) [22
]. One study indicated that the immune-reaction to tumors in individuals with blood group A was reduced compared with the non-A blood group individuals [12
]. Recently, one paper published in Nature
journal indicated that the erythrocyte receptor-ligand pair is essential for erythrocyte invasion in the pathogenesis of malaria. They found that Ok blood group antigen, a kind of blood group antigen, is a receptor for erythrocyte invasion of the parasite [24
]. This discovery suggested that individuals with the A blood group antigen may be more susceptible to H. pylori
invasion. Therefore, we further analyzed the infection status in our gastric cancer cohort and found that the ratio of H. pylori
infection in blood group A cases was significantly higher than that in non-A blood group cases. Recently, Nakao et al
. analyzed the ABO genotype and the risk of gastric cancer, atrophic gastritis and H. pylori
infection, and proposed that the risk for gastric cancer, atrophic gastritis and H. pylori
infection was increased in AA genotype [25
]. This finding is consistent with our data. H. pylori
plays an important role in the development of gastric ulcer and gastric cancer. H. pylori
is a Gram negative bacteria, which can be divided into cytotoxin-associated antigen (CagA) and vacuolating cytotoxin (VacA) positive strains, as well as CagA and VacA negative strains. CagA positive H. pylori
suggest a considerably increased risk of gastric cancer [26
]. The adhesion molecule system of H. pylori
helps the bacteria colonizing in stomach mucosa. The most important adhesion molecular is blood group antigen-binding adhesion A (BabA). Adherence by H. pylori
increases the risk of gastric disease. Animal experiments revealed that BabA could stimulate the inflammatory cells to release more interleukin-8, CCL5 proinflammatory cytokines and precancer-related factors (CDX2 and MUC2) [27
]. Since inflammatory response to H. pylori
infection plays an important role in cellular proliferation and gastric mucosal damage, the upregulation of proinflammatory cytokines in people with chronic gastritis may be an important clinical implication in gastric carcinogenesis.