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Gastric LP accounts for about 10% of all gastric cancers but the exact prevalence in the general population is unknown. Gastric LP predominantly affects individuals of Asian origin (Korean, Chinese, Taiwanese and Japanese populations) but it is becoming more frequent in Europe. Females are slightly more frequently affected than males.

The age of onset is lower than that of classical gastric carcinoma, with onset frequently before 40 years of age, sometimes in very young patients (20 to 25 years of age). Signs and symptoms are nonspecific: satiety, nausea and vomiting, epigastric pain, and weight loss. Patients may present progressive dysphagia. Gastric LP is characterized by malignant glandular proliferation of independent cells (signet-ring cells) in the fibrous stroma leading to thickening and rigidity of the gastric wall. The most common sites of gastric LP are the antral and pyloric regions. Unlike other stomach cancers, gastric LP frequently extends into the peritoneum and lymphatic system. Gastric LP may be primary or occur secondary to infiltrating lobular carcinoma of the breast.

LP is generally a sporadic disease but familial cases have been described. Etiology is unknown. The PSCA gene, that appears to be involved in regulating gastric epithelial cell proliferation, may be a susceptibility gene for diffuse-type gastric cancers. Mutations in E-cadherin gene (CDH1, 16q22.1) were detected in several affected members from one family with gastric LP.

Diagnosis is often problematic as the gastric mucosa is frequently spared from malignant invasion. It requires morphologic studies revealing an infiltrating stomach tumor, and is based on histopathologic findings including signet-ring cells and a fibrous stroma. Multiple endoscopic biopsies are needed. Endoscopic ultrasonography shows a thickening of the submucosal layer of the tumoral wall (up to 10 to 20 mm). CT scan and endoscopic ultrasound may be useful for the diagnosis and for evaluation of local extension.

The differential diagnosis should include malignant diseases (adenocarcinoma and lymphoma) and some benign diseases with thickening of the gastric wall (Menetrier's disease, lymphoid hyperplasia and amyloidosis; see these terms).

Treatment options include surgical resection (mainly total gastrectomy) for localized disease. However, surgery with curative intent is possible in only 20% to 25% of cases due to the very high incidence of peritoneal and distant lymph node involvement. In these cases, chemotherapy provides the only alternative treatment but its efficacy is often limited in this form of cancer. The beneficial effects of adjuvant radiochemotherapy after complete excision of the primary tumour seem to be less pronounced for gastric LP than those observed for the classical form of gastric adenocarcinoma.

Gastric LP has a very poor prognosis due to the frequent occurrence of peritoneal dissemination, lymphatic invasion and extension toward neighboring organs. The 5-year survival rate is around 10-20% in Japan and Europe.