A 53-year-old woman has had nausea, vomiting, and mid-epigastric pain for 5 months. On physical examination, there are no significant findings. An abdominal CT scan shows gastric outlet obstruction. Upper gastrointestinal endoscopy shows an ulcerated 2x4 cm bulky mass in the antrum at the pylorus. A urease test is positive. Which of the following neoplasms is most likely to be seen in a biopsy specimen of this mass?

The most likely cause of a large mass lesion in the stomach is a gastric carcinoma, and this lesion is an adenocarcinoma, likely the intestinal type found in the antral region. Adenocarcinoma is related to Helicobacter pylori infection, with the b-catenin mutation. The incidence of this type of gastric cancer has been decreasing for decades in places where food processing methods have improved. Malignant lymphomas and leiomyosarcomas are less common and tend to form bulky masses in the fundus. Neuroendocrine carcinomas are rare. Squamous cell carcinomas typically appear in the esophagus.