The stomach is covered with mucosa, under which there is a loose connective tissue layer (submucosa) and outermost a muscular layer (muscularis propria). The mucosa in the upper part of the stomach contains closely lying glands with parietal and chief cells. Chief cells produce pepsinogen and parietal cells secrete acid. In addition, the glands in corpus and fundus, also contains ECL (enterochromaffin-like) cells. ECL-cells secrete histamine and are involved in the development of endocrine tumors of the corpus and fundus.
In the distal part of the stomach there are less compact glands producing neutral mucus. This part of the stomach contains other types of endocrine cells producing gastrin (G-cells), sertonin (EC-enterochromaffin) and somatostatin (D-cells). The surface and the pits are covered with a mucus-producing epithelium. In a limited zone between the stomach and the esophagus (cardia) the mucosa is very similar to the mucosa in the pyloric region.
Classification of adenocarcinoma precursor lesions
- Intestinal metaplasia
- Indefinite for intraepithelial neoplasia
- Low-grade intraepithelial neoplasia
- High-grade intraepithelial neoplasia
It is important that intraepithelial neoplasia/dysplasia lesions are evaluated by experienced pathologists before surgery is performed. This is due to the fact that epithelial changes in gastritis and ulcer can imitate dysplasia, and long experience is necessary to evaluate and grade the dysplasia in these specimens.
Classification of adenocarcinoma
- Variants of adenocarcinomas (papillary, tubular, signet-ring cell, mucinous, adenosquamous)
The majority of malignant tumors in the stomach are adenocarcinomas. Laureen divided these into a diffuse and intestinal type, a classification which is of epidemiological as well as prognostic impact. Intestinal type metastasizes hematogenously to the liver, whereas the diffuse type has a tendency to spread to the peritoneum with carcinomatosis.
In contrary to adenocarcinoma in the colon, an adenocarcinoma in the stomach is considered an invasive adenocarinoma when infiltrating cells is detected in the lamina propria. This tumor is designated as intramucosal carcinoma. They are included in the terminology ‘early gastric cancer’ and has a relatively good prognosis compared to those with deeper infiltration.