I. Epidemiology
Stomach cancer has a high incidence in many countries around the world, and China is one of the high incidence areas. Since screening for stomach cancer is not carried out in our country at this stage, in many cases, it is often diagnosed only at an advanced stage, resulting in unsatisfactory treatment effect of stomach cancer.
Who are vulnerable to stomach cancer
Stomach cancer is a chronic disease with a long and complicated pathogenesis. At present, no single factor has been proved to be the direct cause of human gastric cancer. The occurrence of gastric cancer is related to many factors. Currently, the risk factors of gastric cancer are considered to include: Helicobacter pylori infection, smoking, high-salt diet and other dietary factors such as spoiled food, smoked food and pickled products; in addition, the incidence rate of those with family history of gastric cancer is increased. Specifically divided into.
1, certain chemicals: represented by N-nitroso compounds (NOC), which is a general term for a class of chemical substances of nitroso group (-NO), and can be divided into nitrosamines, nitrosamides, nitroso amino acids, nitrosopeptides, etc.
2.Dietary factors: Stomach cancer is related to high salt diet and salted food intake. High concentration of sodium chloride can directly destroy gastric mucus barrier and prolong gastric emptying time, which indirectly promotes carcinogenic substances to enter epithelial target cells of gastric mucosa. High salt can also directly damage the gastric mucosal epithelium and lead to regenerative epithelial proliferation. Polycyclic aromatic hydrocarbon compounds are carcinogens that can contaminate food or form during food processing. Such as while in the samples of smoked fish and bacon found that these foods have a more serious contamination of PAH compounds.
3, Helicobacter pylori (HP) infection: The results of a large number of population-described epidemiological, cohort and case-control studies have shown a positive correlation between H. pylori infection and gastric cancer prevalence. Regarding the mechanism by which HP infection affects gastric carcinogenesis, it is currently believed to have a pro-cancer effect mainly by inducing an inflammatory response in the gastric mucosa leading to regeneration of gastric mucosal epithelial cells. In addition, HP can also activate monocytes to synthesize endogenous genotoxic substance oxynitrite molecules.
4.Genetic factors: Genetic quality is also very important to the development of gastric cancer. The phenomenon of family gathering of gastric cancer and the fact that it can occur in the same sibling supports this view. In the survey of gastric cancer patients, the proportion of first-degree relatives suffering from gastric cancer is significantly higher than that of second- and third-degree relatives. The risk of developing gastric cancer is higher in relatives of diffuse gastric cancer than intestinal type gastric cancer.
5.Other factors: There are several case-control and prospective studies worldwide showing that smoking has a certain relationship with the development of gastric cancer, with the relative risk ranging from 1.4 to 4.8. Certain occupational exposures such as coal mine, asbestos, rubber and other chemical industry workers have a relatively high incidence of gastric cancer; mental trauma, culture and low standard of living are also indirectly related to the incidence of gastric cancer; alcohol consumption, mold-contaminated food and gastric cancer seem to have a certain association, but further research is needed to confirm because the strength of the association is weak and the repeatability is not enough.
Precancerous diseases and precancerous lesions: from normal gastric mucosal epithelium to cellular carcinogenesis often need to go through a long evolutionary stage. The World Health Organization classifies chronic precancerous diseases and precancerous lesions such as gastric ulcer (GU), gastric polyp (GP), residual stomach after partial gastrectomy (GS), chronic atrophic gastritis (CA G), heterogeneous hyperplasia of gastric mucosal epithelium (DYS), and intestinal epithelial hyperplasia of gastric mucosa (IM) as precancerous states of the stomach. These precancerous states have a pathogenetic link with gastric cancer, so they need to be actively dealt with.
Common symptoms of gastric cancer
Early gastric cancer often has no obvious symptoms, the patient’s general condition is generally good and there are few local signs, so it often fails to attract sufficient attention of patients and examiners and is misdiagnosed. However, such symptoms are not unique to gastric cancer and are often similar to chronic diseases such as gastritis and ulcer disease. The main clinical manifestations include epigastric distention and pain, emaciation, weakness, loss of appetite, anemia, nausea, vomiting, bleeding and black stool, in addition, patients may sometimes have diarrhea and/or constipation or lower abdominal discomfort, or fever.
In some cases, symptoms of metastases, such as ovarian or perisplenic masses, may appear first. In terms of physical signs, early gastric cancer often has no obvious physical signs, sometimes there is deep pressure pain in the upper abdomen sometimes accompanied by mild muscle resistance feeling. Upper abdominal masses, anterior rectal fossa masses, umbilical masses and enlarged left supraclavicular lymph nodes are all signs of advanced gastric cancer and/or metastases, especially metastases in left supraclavicular lymph nodes are the most common. These signs not only have diagnostic significance but also have practical significance in deciding the treatment plan.
Diagnosis
An ideal and complete diagnosis should achieve four goals: localization, quantitative, qualitative and periodic.
Commonly used examination methods
1.Gastroscopy
Gastroscopy is an effective method to diagnose gastric cancer because it can directly see the location and extent of gastric mucosal lesions. It is generally believed that the diagnosis rate of gastroscopy for progressive gastric cancer is over 90% with naked eyes. For early gastric cancer, the combined application of endoscopy with cytological examination and pathological examination, as well as the combination of staining method and fluorescence method, can greatly improve the positive diagnosis rate. Due to the popularity of gastroscopy, it has replaced barium meal as the first choice in gastric cancer screening.
2.X-ray imaging
X-ray imaging can determine the location, size and invasion degree of tumor, which is of great significance for the analysis of tumor nature, estimation of operation possibility and prognosis. At present, the main methods are gastric barium meal imaging and gastric gas-barium double contrast imaging, and gastric barium meal imaging has been gradually replaced by gastric double contrast imaging, but because of the cheap price and simple technique, barium meal imaging is still adopted by many hospitals.
Gastric gas-barium double contrast imaging has unique effect on the diagnosis of gastric cancer, especially early gastric cancer, because it can clearly show the fine structure of gastric mucosa, i.e., the condition of gastric cell. Although the advantages of X-ray imaging in the diagnosis of gastric diseases have been challenged by many examination methods, its fundamental role is still undeniable because it can show the morphology and function of the stomach.
3.Ultrasound diagnosis
With the popular application of water-filled gastric cavity method and gastric ultrasound imaging solution, ultrasound examination has been highly valued by clinicians for the diagnosis of gastric cancer. It is simple, easy to perform, non-invasive, and not subject to any limitation, so it is easy to be accepted by patients, especially suitable for old, weak and serious patients. For those who are clinically suspected of gastric cancer but cannot perform endoscopy for various reasons, it has become a screening test.
In addition, endoscopic ultrasound can clearly show the layers of gastric wall and the structures of adjacent tissues or organs outside the lumen, and can accurately assess the extent of tumor invasion, lymph nodes and extragastric metastases. submucosa and plasma layer. In addition to the gastric wall, perigastric lymph nodes, perigastric organs including pancreas, spleen, left kidney and left liver can also be explored.
4.CT diagnosis
With the introduction of spiral CT, it has overcome the limitations of scanning speed, breathing artifacts and post-processing function of ordinary CT, and has higher density resolution, which can show the whole layer of gastric wall, adjacent tissues and organs, and is useful for localization, quantification and regular diagnosis of gastric cancer, so that it is no longer limited to the diagnosis of gastric cancer metastases. At present, CT scan of gastric cancer mainly adopts three-stage enhancement scan technique after hypotonic water filling and intravenous mass injection of contrast agent, and the normal gastric wall mostly presents two to three layers of structure, which are mucosal layer, submucosal layer and muscle-plasma layer.
The main bases of CT performance for the diagnosis of gastric cancer are: thickening of gastric wall, soft tissue mass, abnormal enhancement of tumor area and destruction of multilayer structure of gastric wall, etc.
5.MRI diagnosis
In recent years, with the progress of MRI instruments and imaging software, as well as the use of gastrointestinal relaxants to inhibit gastrointestinal motility, better quality MRI images of stomach and adjacent organs can be obtained, which have the following three advantages compared with CT.
(i) Multiplanar imaging capability, which minimizes the effect of volumetric effects.
(ii) Multi-parametric imaging capability, which can better display enlarged lymph nodes, abnormal soft tissue masses and invasion of intra-abdominal organs through the difference in contrast of each organ tissue.
(iii) The flow-space effect allows MRI to distinguish lymph nodes from blood vessels without the need for contrast. Therefore, MRI can also provide a lot of information for surgery, and is a valuable examination method for gastric cancer.
6.PET-CT diagnosis
Combining PET and CT can effectively show the specific scope of lesions and the involved parts, and can understand the metastasis of other parts. However, due to its high price, it is generally not used as a routine examination.