To the Editor: Numerous reports have pointed to an increased prevalence of blood type A in patients with gastric cancer. Aird et al (1) were the first to study ABO blood groups in a large number of patients with gastric cancer, noting an excess of group A, and a deficiency of group O, in comparison with control patients. Subsequently, at least 77 controlled series have been published; in 55 of these, cancer patients had an excess of group A, in 14 a slight predominance of group A, in only 2 a deficiency of group A. (2) In a recent study aiming at the study of the association of gastroduodenal disease phenotype with ABO blood group and Helicobacter pylori virulence genes, we ...