Tumours of the stomach and small intestine

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Tumours of the stomach and small intestine

Carcinoma of stomach

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:

• Fungating tumours—these polypoid lesions may grow to a huge size

• Malignant ulcers—these probably result from necrosis in broad-based solid tumours. Malignant ulcers are often larger than peptic ulcers (except for giant benign ulcers of the elderly) with a heaped-up indurated (hardened) margin

• Infiltrating carcinomas—this form spreads widely beneath the mucosa, and diffusely and extensively invades the muscle wall. This causes thickening and rigidity and the entire stomach contracts to a very small capacity. This is known as linitis plastica and its appearance likened to a ‘leather bottle’. Linitis plastica affects a slightly younger age group than intestinal-type cancer and has a very poor prognosis. Diagnosis may be delayed because endoscopic changes are often subtle and standard biopsies of mucosa may not show malignancy

‘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

Helicobacter pylori infection

H. pylori is known to initiate peptic ulceration, and chronic H. pylori infection has become a prime suspect for initiating intestinal-type gastric cancer. The organism can colonise gastric mucosa over long periods and cause chronic gastritis which may progress to type B multifocal atrophic gastritis. In one biopsy study of gastric cancers, H. pylori was found in 90% of intestinal-type cancers, whilst only 30% of the diffuse type were infected. The carcinogenic mechanism of H. pylori may involve alterations to the gastric acid–pepsin environment, with increased cell turnover and possibly enhanced mucosal susceptibility to ingested carcinogens. H. pylori eradication does not reverse gastric atrophy but does improve the enzymic and hormonal secretory capacity of the stomach. H. pylori also appears likely to be involved in gastric lymphoma of the mucosa-associated lymphoid tissue (MALT) type (see p. 322).

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.

Box 23.1   Presenting features of gastric carcinoma

Spread of gastric cancer

Invasive gastric cancer progresses to involve submucosal lymphatics, and the depth of penetration through the gastric wall correlates closely with the likelihood of nodal metastases. The TNM system is now the standard staging structure agreed internationally, with additional Japanese nomenclature designating particular groups of lymph nodes draining the stomach as stations, numbered 1–16. Lymphatic metastatic spread initially involves nodes in the coeliac axis and periduodenal area; these are known as perigastric stations 1–6. Involvement of these is considered N1 in the TNM system. Positive nodes in the para-aortic area, splenic hilum and porta hepatis indicate a more advanced stage, with porta hepatis nodes sometimes causing obstructive jaundice. Involvement of these ‘secondary’ stations signals N2, N3 or even M1. Clearance of more distant lymph node stations is achieved by the radical R2 gastrectomy (pioneered in Japan). Node histology enhances the accuracy of TNM staging and improves the ability to predict long-term survival after surgery.

Investigation of suspected gastric carcinoma

Initial diagnosis

Early detection radically increases the chances of curing the condition. A high index of suspicion and early endoscopy for non-specific symptoms improve these chances. In one American series where early endoscopy was the rule, only 15% of gastric cancers were unsuitable for operation at initial diagnosis, and half the operations were performed with the aim of cure.

In areas with a high incidence of gastric cancer, endoscopic screening (Fig. 23.2) is an effective and popular method of detecting early disease. It is widely employed in Japan, with the result that over 40% of cancers operated upon after screening have been in a pre-symptomatic stage and can truly be defined histologically as ‘early gastric cancer’. About 90% of these patients undergo potentially curative operations.

Barium meal used to be the standard investigation but it was difficult to differentiate between benign gastric ulcer and carcinoma. The radiological appearances of a typical gastric malignancy is shown in Figure 23.3 for historical reasons. Endoscopy, which allows visual inspection and biopsy, is now the standard investigation for suspected carcinoma of the stomach. The site of a lesion may be important as benign ulcers are usually found on the lesser curve or in the prepyloric area whereas carcinomas arise in any part of the stomach. The initial endoscopy in a patient found to have carcinoma gives an accurate diagnosis in 90% of those with exophytic lesions (where the tumour grows out into the lumen) but only 50% for infiltrating lesions. Multiple biopsies improve these rates, as do repeat endoscopy and re-biopsy of suspicious lesions.

Case History

Staging

Once cancer is diagnosed, knowing the stage helps determine the most appropriate treatment and whether surgery is likely to benefit the patient. CT scanning of chest and abdomen is often the first investigation, and many patients are found to already have local tumour invasion, lymph node involvement and hepatic metastases at this stage. If the CT scan is clear, laparoscopy improves the accuracy of staging, and is an important way to identify serosal involvement, omental disease and small liver metastases not seen on CT scanning. Endoscopic ultrasonography (EUS) via a flexible endoscope is highly accurate for determining the depth of penetration of small gastric cancers, and hence the ‘T’ (tumour) stage. Local spread (e.g. into pancreas), nodal involvement, left hepatic lobe metastases and ascites are also demonstrable by this method. Finally Fluorodeoxyglucose positron emission tomography (FDG-PET), known as PET scanning, is increasingly used to search for metastatic disease not identified by any other modality.

Management of gastric carcinoma

Like oesophageal cancer, gastric cancer is increasingly managed in specialist centres. This consolidates surgical, radiological and oncological expertise and ensures that other professionals such as anaesthetists, theatre staff, ITU/HDU staff, dieticians and physiotherapists become experienced in managing these cases and can all contribute to a multidisciplinary team (MDT).

Radical surgery

As described, metastasis from gastric cancer is often early, widespread and occult. For this reason, radical surgery offers the only prospect of cure even when the tumour appears small. Radical gastrectomies are very major operations and careful staging is needed to ensure that there is a realistic chance of cure, together with thorough assessment of general fitness.

Japanese surgeons have developed radical R1 and R2 gastrectomies for patients where cure is the intention. Both involve total or subtotal gastrectomy; R1 also removes local nodal stations whilst R2 removes local and secondary nodal stations. In Japan, if the cancer proves to be confined to mucosa and submucosa, 5-year survival approaches 90%; with local node involvement, survival is about 50%. With more distant spread, survival falls dramatically to 5%. Western results have not yet matched these, largely because of higher surgical complication rates.

Gastrointestinal stromal tumours (GIST)

Gastrointestinal stromal tumours are rare mesenchymal tumours that can arise anywhere in the GI tract. They were once thought to be leiomyomas because of the histological similarity but immunocytochemical markers can now distinguish mesenchymal tissue types and differentiate them from muscle and nerve tumours. GISTs have now been identified as originating from the interstitial cells of Cajal, the so-called ‘pace-makers’ of gut motility. GISTs are most frequently found in the stomach and can range from < 1 cm to > 20 cm. The risk of malignancy is determined partly by tumour location but mostly by size and histological mitotic index (see Table 23.1). Most gastric GISTs are small (< 5 cm) and have a low mitotic index.

Table 23.1

Risk of aggressive behaviour of gastrointestinal stromal tumours (GIST)

Risk of aggressive behaviour (malignant potential) Greatest dimension (cm) Mitoses per 50 microscope high-power fields
Very low < 2 < 5
Low 2–5 < 5
Intermediate < 5 6–10
  5–10 < 5
High > 5 > 5
  > 10 Any number
  Any size > 10

GISTs are often diagnosed incidentally at endoscopy. They can be sessile (domed) or pedunculated intramural lesions covered by normal mucosa (Fig. 23.4b). Small lesions may be asymptomatic; large lesions produce symptoms or signs of any abdominal mass. Gastric tumours are prone to haemorrhage via a central ‘umbilicated’ ulcer (Fig. 23.4a); these are typically found after an acute episode of haematemesis. Following diagnosis and before surgery, the patient may need to be staged by CT to confirm the size and exclude metastases (local, nodal or hepatic). Suitable biopsies allow immunocytochemical analysis, but it can be difficult to obtain sufficiently deep samples. Local resection is appropriate if the lesion has low malignant potential; malignant lesions require full oncological clearance as for other gastric cancers.

Case History

GIST tumours are highly resistant to traditional chemotherapy; however, the c-kit tyrosine kinase inhibitor imatinib (Glivec) is highly effective for advanced and metastatic disease and has improved 2-year survival rates to 75–80%.

Small bowel gastrointestinal stromal tumours

GISTs of small bowel are histologically similar to gastric tumours but may present by obstructing the lumen or growing out from the serosal surface of the bowel (Fig. 23.5). Primary resection and anastomosis is the usual treatment and survival is influenced by the size and mitotic counts.

Case History

Gastric and small bowel lymphomas

Pathology and clinical features of lymphomas

Primary lymphomas sometimes arise in the stomach or small bowel. They constitute about 10% of gastric malignancies. As with peptic ulcer and intestinal-type gastric adenocarcinoma, H. pylori infection is an important initiating factor. In non-Hodgkin lymphoma, small bowel lymphoid tissue may become involved.

In the stomach, most lymphomas are non-Hodgkin lymphomas of B-cell origin. They may become extensive, diffusely infiltrating the stomach wall or, less often, projecting into the lumen as bulky ulcerating masses. The symptoms and endoscopic appearances closely resemble gastric adenocarcinoma but recognising lymphoma is important because the treatment is very different and the prognosis much better. Unlike gastric carcinoma, lymphomas tend to occur in children and young adults. Some cases of low-grade lymphoma involving the mucosa-associated lymphoid tissue or ‘MALToma’ have been reported to resolve following Helicobacter eradication, but this is only successful if the disease is detected early.

In the small intestine, lymphomas also produce bulky lesions which may obstruct, ulcerate, bleed or even perforate. Occasionally, a lymphoma provides the focus for an intussusception (see Figs 23.6 and 23.7 and also Fig. 50.12, p. 624). Small bowel lymphoma may be a complication of coeliac disease but the risk is only about six times higher than for the general population.

Case History

Case History

Carcinoid tumours

Clinical presentation of carcinoid tumours

Appendiceal carcinoid tumours are usually discovered incidentally in appendicectomy specimens and virtually always remain small and benign. In contrast, carcinoid tumours elsewhere spread locally in the bowel and mesentery, later becoming disseminated to the liver and other sites. The bowel lesions themselves usually present with symptoms of partial or complete obstruction.

Carcinoid tumours secrete a variety of catecholamines, including serotonin. When there is a large volume of tumour, usually in the form of liver metastases, enough catecholamines are secreted to cause the carcinoid syndrome. This is characterised by an array of clinical phenomena including transient ‘hot flushes’, hypotension, asthma and diarrhoea. A metabolite of serotonin, 5-hydroxy-indoleacetic acid (5-HIAA), can be measured in the urine as a diagnostic marker.

Management of carcinoid tumours

Treatment usually involves excising the primary lesion along with local lymph nodes. An appendiceal carcinoid present at the tip only and less than 2 cm in diameter can be treated by simple appendicectomy. In patients with metastatic disease, the condition progresses very slowly. It responds well to surgery, and in the typical young patient a more radical approach can be recommended than for other intra-abdominal malignancies. Metastatic carcinoid is not curable by radiotherapy or chemotherapy.

The full carcinoid syndrome is usually associated with large volume hepatic metastases. It is uncommon and symptoms can be controlled with the help of drugs such as octreotide, a somatostatin analogue. Radiotherapy is useful if pain is caused by massive liver enlargement as it may induce some shrinkage.

Other tumours of the small intestine

Small bowel tumours include solitary benign angiomas. These are usually found incidentally at operation or autopsy but sometimes present with intussusception or chronic haemorrhage.

Adenocarcinomas do occur in the small intestine, especially in the duodenum, but are rare compared with stomach and large bowel. Small bowel adenocarcinomas present with bowel obstruction, biliary obstruction when in the periampullary region, bleeding or symptoms of metastases. Barium follow-through examination for chronic symptoms may demonstrate the lesion, but more commonly it is found and resected at a laparotomy for acute obstruction, only being recognised on histological examination. Unfortunately, metastasis to regional lymph nodes or the liver has already occurred in many patients by the time of presentation.

Peutz–Jeghers syndrome is described in Chapter 27 (p. 353).

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