Type I: Good prognosis associated with atrophic gastritis, usually multiple, presence of hypergastrinemia, and vitamin B12 deficiency; Type II: uncertain malignant potential, usually multiple, associated with hypergastrinemia in patients with gastrinomas and/or multiple endocrine neoplasias (MEN-1); Type III: Aggressive, often isolated and gastrin normal levels. Here, GAST is linked to gastrin-producing neuroendocrine tumor.