INTRODUCTION — Gastric cancer has been described as early as 3000 BC in hieroglyphic inscriptions and papyri manuscripts from ancient Egypt. The first major statistical analysis of cancer incidence and mortality (using data gathered in Verona, Italy from 1760 to 1839) showed that gastric cancer was the most common and lethal cancer. It has remained one of the most important malignant diseases with significant geographical, ethnic, and socioeconomic differences in distribution.
This topic review will focus on the epidemiology of gastric cancer. Risk factors are presented separately. (See "Risk factors for gastric cancer".)
INCIDENCE — Gastric cancer is one of the most common cancers worldwide [1]. Approximately 22,220 patients are diagnosed annually in the United States, of whom 10,990 are expected to die [2]. Global, country-specific incidence rates are available in the World Health Organization GLOBOCAN database.
Gastric cancer used to be the leading cause of cancer deaths in the world until the 1980s when it was overtaken by lung cancer [3,4]. The worldwide incidence of gastric cancer has declined rapidly over the recent few decades [5-9]. Part of the decline may be due to the recognition of certain risk factors such as H. pylori and other dietary and environmental risks. However, the decline clearly began before the discovery of H. pylori. The decline first took place in countries with low gastric cancer incidence such as the United States (beginning in the 1930s), while the decline in countries with high incidence like Japan was slower. In the United Kingdom, there was a consistent decline in incidence of gastric cancer, with a reduction in relative risk from 1.14 in 1971 to 1975 to 0.84 in 1996 to 2000 in males, and 1.18 in 1971 to 1975 to 0.81 in 1996 to 2000 in females [10]. In China, the decline was less dramatic than other countries; despite an overall decrease in gastric cancer incidence, an increase has been observed in the oldest and the youngest group, and a less remarkable decline has been observed among females than in males [11]. Of note is that the age of onset of developing gastric cancer in Chinese population is younger than that in the West. In the United States, risk factors for noncardia gastric cancer include male sex, Native American or Asian American/Pacific Islander race, and older age [12]. Between 1977 and 2006, the incidence rate for noncardia gastric cancer in the United States declined among all race and age groups except for White Americans aged 25 to 39 years for whom it increased [13]. The rise in incidence of noncardia gastric cancer among those at 25 to 39 years is noteworthy, since this may signal the introduction of new environmental factors.
An interesting hypothesis is that the popularization of refrigerators marks a pivotal point for the decline [14,15]. Refrigerators improved the storage of food, thereby reducing salt-based preservation of food and preventing bacterial and fungal contamination. Refrigeration also allowed for fresh food and vegetables to be more readily available, which may be a valuable source of antioxidants important for cancer prevention.
Despite the decline, the absolute number of new cases per year is increasing, mainly due to aging in the world population. Furthermore, for unclear reasons, the trend toward declining incidence has been interrupted and replaced by an upward trend in young patients in recent years [16]. Thus, gastric cancer will continue to represent an important cause of cancer and cancer-related mortality for the foreseeable future.
GEOGRAPHICAL VARIATION — The incidence of gastric cancer varies with different geographic regions. Rates are highest in Eastern Asia, Eastern Europe, and South America, while the lowest rates are in North America and parts of Africa (figure 1) [1]. Over 70 percent of gastric cancers occur in resource-limited countries [1]. Gastric cancer is more common in males than in females, in both resource-abundant and resource-limited countries (figure 2A-B).
There are also substantial differences in incidence among different ethnic groups within the same region (see below). A difference in incidence and mortality from north to south has been observed in several countries, with the northern areas having a higher mortality risk than those in the south. This gradient is particularly marked in the northern hemisphere [17-19], whereas in the southern hemisphere, the mortality risk tends to be higher in the southern parts [20,21].
In Japan, there appears to be a north/south divide, with gastric cancer mortality and incidence higher in the northeastern prefectures [22]. In England and Wales, there is a twofold difference in mortality and incidence rates across the country, with lower levels in the south and east and higher levels in the north and west, particularly noticeable in northwest Wales [23]. In China, the incidence and mortality of gastric cancer varies from province to province (generally very high in the north, but relatively low in the south) [19,24]. It appears that higher geographic latitudes are associated with a higher gastric cancer risk.
MIGRATION STUDIES — Migration, and in particular, international migration, can lead to a change in risk, as the immigrants, especially second and third generations, adopt the lifestyle and consequently the local disease patterns. Studies of Japanese migrants to the Unites States have confirmed that early exposure to environmental rather than genetic factors have a greater influence on mortality and incidence rates [25,26]. In the subsequent generations born in the United States, the mortality rate declined towards the lower rate of White Americans.
CHANGE IN HISTOLOGY PATTERN — The diffuse and intestinal types of gastric cancer as classified by Lauren [27] describe two biological entities that are different with regard to epidemiology, etiology, pathogenesis, and behavior (see "Gastric cancer: Pathology and molecular pathogenesis", section on 'Intestinal versus diffuse types'):
●Intestinal gastric cancer is more common in males and older age groups. It is more prevalent in high-risk areas and is likely linked to environmental factors.
●The diffuse or infiltrative type, is equally frequent in both sexes, is more common in younger age groups, and has a worse prognosis than the intestinal type.
There has been a worldwide decline in the incidence of the intestinal type in recent few decades that parallels the overall decline in the incidence of gastric cancer. By contrast, the decline in the diffuse type has been more gradual. As a result, the diffuse type now accounts for approximately 30 percent of gastric carcinoma in some reported series [28].
Despite the decline in gastric cancer overall, there has been an explosive increase in incidence of cancer of the gastric cardia (figure 3) [29-31]. The shift from distal to proximal stomach may in part be due to the decrease in the distal cancers. However, it has also been proposed that carcinoma at the cardia is a different entity from that of the rest of the gastric carcinoma.
The proximal tumors share demographic and pathological features with Barrett's associated esophageal adenocarcinoma and are more likely to occur in men, which parallels the male predominance in the increasing incidence of carcinoma in the lower third of the esophagus. The proximal tumors also differ from distal tumors in that they are not associated with a severe form of gastritis characterized by atrophy and/or intestinal metaplasia. Furthermore, they tend to be more aggressive than those arising from distal sites. Environmental factors or chemical carcinogens (eg, cigarette and alcohol) may be more strongly associated with cardiac carcinomas compared with more distal carcinomas [32]. (See "Epidemiology and pathobiology of esophageal cancer".)
MORTALITY — Global, country-specific mortality rates are available in the World Health Organization GLOBOCAN database. There has been a steady decline in gastric cancer mortality. A study of gastric cancer mortality in Europe and other areas of the world between 1980 to 2005 demonstrated an annual percent change (APC) in gastric mortality rate around -3 to -4 percent for the major European countries. The APC rates were similar for the Republic of Korea (-4.3 percent), Japan (-3.5 percent), Australia (-3.7 percent), and the United States (-3.6 percent). In Latin America, the decline was less marked, but constant (-1.6 to -2.6 percent) [33].
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Gastric cancer".)
SUMMARY AND RECOMMENDATIONS
●Gastric cancer remains one of the most common forms of cancer worldwide. (See 'Introduction' above.)
●The worldwide incidence of gastric cancer has declined rapidly over the recent few decades, the reasons for which are incompletely understood. However, the rate of decline has been variable in different regions.
●The incidence of gastric cancer varies with different geographic regions. The highest incidence rates are in Eastern Asia, the Andean regions of South America, and Eastern Europe, while the lowest rates are in North America, Northern Europe, and most countries in Africa and South Eastern Asia. There is also substantial difference in the incidence among different ethnic groups within the same region. (See 'Geographical variation' above.)
●The histologic pattern of gastric cancer is also changing with a decline in the intestinal type compared with the diffuse type. (See 'Change in histology pattern' above.)
●There has been a steady decline in gastric cancer mortality worldwide, although the rate of decline differs by region. (See 'Mortality' above.)
