Epidemiology
Gastric cancer is the sixth most common cancer in the UK, accounting for 5% of all cancers. Worldwide it is the second most common cancer. The male:female ratio is around 1.8:1 and 95% of cases are diagnosed in people aged 55 or older, with an average age at presentation of 65 years.
The incidence of gastric cancer has fallen in the developed world, possibly due to better food preservation. It is more common in people with blood group A (20% increased risk). There are extreme variations by geographical location, 40% of cases occur in China, where it is the most common cancer, but age-adjusted incidence rates are highest in Japan with diet as the main contributing factor.
Aetiology
Dietary carcinogens can contribute to an increased risk of gastric cancer, especially nitrosamines and a diet high in salty foods (e.g. in Japan). Helicobacter pylori has been used to explain the aetiology of cancers developing in patients with atrophic gastritis as it is more common in patients with gastric cancer than without. Furthermore, chronic atrophic gastritis leads to a decrease in acid secretion with resulting bacterial overgrowth and an increase in nitrates. This is associated with a threefold increase in risk of gastric cancer. Familial mutations of cadherin-1 gene (CDH1) are associated with an increased risk. The routine use of proton-pump inhibitors without investigation with endoscopy may contribute to late diagnosis. Vagotomy and partial gastrectomy (20 years after surgery) carry an increased risk of gastric cancer. Other risk factors include family history, obesity, radiation and a lower socioeconomic class.
Pathophysiology
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