Introduction

Most gastric tumours are malignant: nearly all are adenocarcinomas, and the rest are lymphomas or else the occasional carcinoid tumour or sarcoma. True adenomatous gastric polyps are rare; most gastric polypoid lesions are small benign hyperplastic nodules.

Tumours of small bowel are rare. Of the malignant tumours, lymphomas and gastrointestinal stromal tumours (GIST) are much more common than adenocarcinomas. Peutz–Jeghers syndrome is a rare inherited disorder characterised by multiple benign polyps in the small bowel and perioral pigmentation plus increased risk of breast, colorectal and other cancers. Patients are fairly commonly encountered at student examinations (see Ch. 27, p. 353).

Pathology of gastric carcinoma

Gastric carcinomas are almost exclusively adenocarcinomas. Two distinct histopathological groups are recognised, each with its own epidemiological associations. The intestinal type has histological features similar to intestinal epithelium. Cells grow in clumps and there is marked inflammatory infiltrate. The second variety is the diffuse type. Here the cells are singular, often arranged in single file and surrounded by a marked stromal reaction. Tumour cells have large intracellular mucin droplets which displace the nucleus to the cell periphery, giving the characteristic signet ring appearance (Fig. 23.1). Intestinal-type carcinomas have a better prognosis than mucin-producing signet ring carcinomas.

Gastric carcinomas develop in three morphological forms described below; the intestinal type largely produces fungating tumours and malignant ulcers, and the diffuse type causes infiltrating carcinomas:

‘Early gastric cancer’ is defined as cancer limited to the mucosa and submucosa. This is found most often as a result of endoscopic screening or whilst investigating possible peptic ulcer. Results of surgery in this group are excellent, with a surgical cure rate of about 90%.

Epidemiology of gastric carcinoma

Gastric cancer is the fourth most common cancer in the world, causing 8% of cancers, but is the second most frequent cause of cancer deaths at 10%; its mortality is surpassed only by that of lung cancer (2008 figures). The disease is rare before the age of 50 and increases in frequency thereafter. Males have two to three times the risk of females, and the disease is more common in lower socio-economic groups. Korea has overtaken Japan in having the highest annual incidence—a crude rate of 70 per 100 000 per year in men and 27 in women (2002). In the UK, equivalent rates are 12.6 for men and 5.2 for women. The offspring of Japanese immigrants to America carry no greater risk than other Americans, evidence that environmental rather than racial factors are central in the aetiology. In much of the Western world, the incidence and death rates of gastric cancer have steadily decreased over recent years, and this is almost entirely due to a decline in the intestinal type. In Japan, the age standardised incidence for men has fallen from 80 per 100 000 per annum in 1975 to 50 in 2005.

The epidemiology gives enticing clues as to the causes of the disease. There are marked regional variations in incidence, largely explained by disparities in the rate of intestinal-type carcinomas. This, and the fact that this type is more prevalent in lower socio-economic groups, suggests that environmental factors are important in its genesis. There is probably no universal aetiological factor but rather a combination of co-factors that bring about malignant change. Japan, with its very high incidence of this disease, continues to play a leading role in research into early detection and management.

Aetiology of gastric carcinoma and premalignant conditions

Clinical features of gastric carcinoma

Symptoms are often minimal until late in the course of the disease so that 70% of patients present with advanced local and/or metastatic disease. Lesions at the inlet or outlet of the stomach cause obstructive symptoms earlier than those elsewhere where the diameter allows for substantial growth before encroachment. Vomiting occurs if the gastric outlet becomes obstructed, typically by tumours of the antrum, and dysphagia occurs with gastro-oesophageal tumours.

In advanced disease, up to half the patients are asymptomatic and the rest have pain, nausea, vomiting, anorexia or a feeling of fullness after small meals (early satiety). Sometimes these symptoms are there months before the patient presents. Anaemia from chronic occult blood loss is common and one-third have positive stool tests for occult blood. One-third have cachexia (severe weight loss and wasting). This usually indicates metastatic disease and may be the only manifestation of cancer at the time. Of the 70% who present with advanced local disease (stage T₃), more than half have extensive abdominal nodal spread and half have distant metastases. The presenting features of gastric carcinoma are summarised in Box 23.1.