A 67-year-old man has had a 4-kg weight loss and nausea for…

A 67-year-old man has had a 4-kg weight loss and nausea for the past 6 months.  The upper endoscopy shows that the entire gastric mucosa is eroded and has an erythematous cobblestone appearance.  The gastrectomy specimen shows small and shrunken stomach with a rigid thickened wall.  Which of the following is most likely the diagnosis?