Provided are methods for preventing initiation and/or progression of gastrin-associated tumors and/or cancers in subjects. In some embodiments, the methods relate to administering compositions that gastrin immunogens to subjects. Also provided are methods for inhibiting development of gastrin-associated precancerous lesions, methods for preventing formation of fibrosis associated with a tumor and/or a cancer, uses of compositions that include a gastrin immunogen to prevent initiation and/or development of a gastrin-associated tumor or cancer and/or for preparing medicaments therefor, and compositions for use in preventing initiation and/or development of gastrin-associated tumors and/or cancers and/or precancerous lesions thereof.