In summary, the results of our in vitro and in vivo experiments indicate that, miR-30a, the complementary sequence of miR-30a-3p and miR-30a-5p, functions as a tumor suppressor by double-targeting COX-2 and BCL9 in H. pylori-infected gastric cancer cells and significantly affects the development of H. pylori-induced gastric cancer, shedding new light on the mechanisms underlying H. pylori-associated gastric cancer (Fig. S8). The gene discussed is BCL9; the disease is gastric cancer.