HP and gastric cancer: Watabe et al. [9] used the combination of the PG method and Hp antibody measurement to investigate the incidence rate of gastric cancer in the following four groups—group A (PG method, negative; Hp antibody, negative), group B (PG method, negative; Hp antibody, positive), group C (PG method, positive; Hp antibody, positive), and group D (PG method, positive; Hp antibody, negative).