A 58-year-old man from rural India presents with progressive early satiety, weight loss of 8 kg over 3 months, and vague epigastric discomfort. Upper endoscopy reveals a diffuse, rigid gastric wall with loss of normal rugal folds and poor distensibility throughout the stomach. Biopsies show signet ring cell adenocarcinoma with extensive submucosal infiltration. The endoscopic appearance is consistent with the pattern marked **D** in the diagram. Which of the following best describes the histological type and its associated clinical significance in this patient?