Multiple gastric neuroendocrine tumors in a patient with parietal cell dysfunction and adenosine triphosphatase H/K transporting subunit alpha gene variant.

A 47-year-old woman presented with multiple gastric tumors, each up to 10 mm in diameter, in the gastric body and fundus without mucosal atrophy. White spots and numerous transparent, light-brownish, small, and rounded spots were observed in the background gastric mucosa. Biopsy specimens obtained from the tumors revealed gastric neuroendocrine tumors. The patient exhibited hypergastrinemia and achlorhydria and tested negative for serum parietal cell antibody, intrinsic factor antibody, and Helicobacter pylori infection. Moreover, no additional lesions were detected on imaging. These findings were inconsistent with Rindi's classification. The tumor was resected via endoscopic submucosal resection. Histopathological examination revealed gastric neuroendocrine tumors G2 infiltrating the submucosa with no atrophy of the gastric mucosa, dilated fundic glands, parietal cell protrusions, and hyperplasia of enterochromaffin-like cells. Immunohistochemically, the parietal cells were negative for both α- and β-subunits of H/K ATPase, suggesting parietal cell dysfunction. A genomic variant was identified in adenosine triphosphatase H/K transporting subunit alpha. After 7 years of treatment, there was no evidence of residual or metastatic lesions. Modification of adenosine triphosphatase H/K transporting subunit alpha may be a significant factor in the pathogenesis of multiple gastric neuroendocrine tumors in the context of gastric parietal cell dysfunction.