Some Current Problems in the Epidemiology of Gastric Cancer
The epidemiology of gastric cancer changed substantially during the course of the past century. These changes were closely connected with social developments [23, 211]. We will discuss the current situation in detail in this chapter.
Tumors of the alimentary tract remain one of the main problems in gastroenterology. On the whole, cancer of the digestive organs is the leading pathology in the structure of oncological morbidity and mortality. The history of the genesis and development of oncology as a major and complex medical field shows that, for a long period of time, gastric cancer remained a kind of basic model for studies of numerous oncological problems. This was quite natural, because during the first decades of the past century it was generally belief that gastric cancer was the most common of all tumoral diseases. Many existing clinicomorphological and diagnostic oncological postulates were studied in detail in gastric cancer patients.
At the present time, the picture of the oncological morbidity and mortality of various cancers worldwide has changed somewhat. According to the International Agency for Research on Cancer (IARC), in 2000, 10.1 million new cases of cancer of all localizations were diagnosed; there were 6.2 million fatal outcomes of cancer and a total of 22 million patients with cancer in the 5-year survival period.
Compared with the figures for 1990, cancer incidence in 2000 increased by 22%. The cancer profile varies within a wide range depending on the parameter studied (morbidity or mortality) [219, 220].
In 2000, 86 700 new cases of gastric cancer were diagnosed (8.4% of all cancer patients). Gastric cancer morbidity is fourth in line of frequency, after cancer of the lungs (1.2 million, or 12.3%), the mammary gland (1.05 million, or 10.4%), and colorectal cancer (94 500, or 9.4%). Nevertheless, gastric cancer mortality has remained consistently in second place for several decades, following only pulmonary carcinoma (10.4% vs 17.8%, respectively; ► Diagrams 1 and 2) [80, 220].
Diagram 1. Structure of global cancer morbidity
Pulmonary cancer 12.3%
Mammary cancer 10.4%
Colorectal cancer 9.4%
Gastric cancer 8.4%
Other cancers 59.2%
Diagram 2. Structure of global cancer mortality
Pulmonary cancer 17.8%
Gastric cancer 10.4%
Cancer of the liver 8.8%
Other cancers 63.0%
In recent years, the incidence of gastric cancer has decreased in some developed countries, and this decrease has been quite substantial in some of them, the mean reduction being 10-19% per decade. Thus, since 1930, the incidence of gastric cancer in the USA has decreased four times, dropping to as low as six to seven cases per 100,000 population. During the past 50 years, it has decreased from 33 to ten per 100,000 cases in male, and from 30 to five per 100,000 cases in female subjects. Nonetheless, gastric cancer remains 7th among malignant tumors in the USA [87, 200]. In 1996, gastric cancer was diagnosed in about 22,800 Americans, and it became the cause of death in 14,000. In Finland, the incidence of gastric carcinoma has decreased by 31% during the past two decades. In Great Britain, Belgium, and Canada, in the countries of Western Europe, North America, and Southern Asia, the situation is relatively positive [149, 237, 276].
The incidence of gastric cancer in the rest of the world is far more significant. Almost two thirds of the overall gastric cancer incidence is in the underdeveloped countries. But the morbidity is also high in some economically developed countries. These include the countries of Eastern Europe, Eastern Asia, South and Central America, some republics of the former Soviet Union, and most African countries.
In Russia, gastric cancer accounts for 12.7% of the overall oncological morbidity, which is much higher than the average world incidence. In men, it stands second (14.7%), in women, third (10.8%) in the list of malignant tumors. As regards cancer mortality, gastric tumors constitute 16.7% [8, 76]. Gastric cancer morbidity is the highest in Korea (70.02 per 100 000 men and 25.02 per 100 000 women) and in Japan (69.2 per 100 000 men and 28.6 per 100 000 women). Survival of gastric cancer patients is relatively high (52%) in Japan, where mass screening by gastrophotofluoroscopy has been performed since the 1960s, the time when the morbidity was dramatically high: 40-45% of overall tumor morbidity. Survival in the USA, Europe, and China varies from 20 to 25% [191, 267].
The relatively good survival rate in Japan is explained above all by early diagnosis of the disease, based on complex examination of the stomach, including primary X-ray with subsequent selective en-
doscopy. As a result, the disease in its first and second stages is diagnosed in 45.7% and 11.9%, respectively, whereas in the USA, where endoscopy dominates the diagnostic techniques, gastric cancer is diagnosed only at its third and fourth stages (35.% and 30.1%, respectively). As a result, the 5-year survival is twice as high in Japan as in the USA [112, 129, 130, 134, 221].
It is quite natural that specialists question why almost 50% of patients in Japan undergo surgery for minor cancer, whereas in the developed countries the percentage of such patients is below 10%, the diagnostic potential being practically similar in these countries. It is the opinion of pathological anatomists that one of the causes of this phenomenon is the different criteria for estimating malignant new growths. Meanwhile, these are decisive in the healthcare system. To be more explicit: Either the patients operated on in Japan had no cancer, or in the other developed countries they do not diagnose cancer early in order to avoid having to operate on the patients in the early stage of the disease. This dispute resulted in adoption of the Vienna classification of gastrointestinal neoplasia in 2000 . According to this classification, morphological changes in the mucous membrane are divided into five groups:
1. Absence of neoplasia and dysplasia - normal mucous membrane, gastritis, intestinal metaplasia
2. Indefinite neoplasia or dysplasia, diagnosed in cases where it is not clear whether the changes are regenerative or neoplastic. Inflamma-tion and atrophic changes interfere with diagnosis.
3. Non-invasive neoplasia of low degree - low degree of dysplasia or adenoma
4. Non-invasive neoplasia of high degree:
a. High-degree adenoma or dysplasia b. Non-invasive carcinoma (carcinoma in situ)
c. Suspected invasive carcinoma
5. Invasive neoplasia a. Adenocarcinoma growing through proper mucous membrane b. Deeper carcinoma
Analysis of the international classification of neoplasia shows that pathomorphologists now agree with those concepts and terms
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