Stomach cancer is the second leading cause of cancer death in the world and one of the most common malignant tumors threatening human health. About 160,000 people die of gastric cancer in China every year, and the incidence of gastric cancer among young people and elderly people over 65 years old has been on the rise in recent years.
The key to improve the prognosis of gastric cancer patients is to do well in secondary prevention, i.e. early detection and early treatment. The 5-year survival rate of patients with progressive gastric cancer is only 30-40% after surgical resection, while the 5-year survival rate of early gastric cancer (EGC), i.e. cancer cells only infiltrate into the gastric mucosal layer and submucosal layer, can be 80-90% after surgical treatment, regardless of whether there is lymph node metastasis or not, and the 10-year survival rate of small gastric cancer (SGC) and micro gastric cancer (MGC) can reach 100%. Therefore, early and accurate detection and treatment of gastric cancer is of great significance to reduce the mortality rate of gastric cancer.
How to detect early gastric cancer
Natural population screening has been shown that mass screening with an interval of 1.5-2 years can help detect early gastric cancer. For example, the Japanese medical profession adopts the air-barium double contrast method of radiological imaging for screening, and then performs gastroscopic precision examination on suspicious cases, which results in the early surgery rate of gastric cancer reaching over 50% and the 5-year survival rate reaching over 90%. At present, China mainly conducts selective local screening in areas with high incidence of gastric cancer, such as age over 35 years old, poor dietary habits such as consuming high salt and moldy food, family history of tumor, etc., and then selects high-risk individuals by comprehensive analysis, and then conducts endoscopy and X-ray radiography. Comprehensive census results from all over China show that the detection rate of gastric cancer in census is about 0.037-0.6%, and early gastric cancer accounts for 15-25% of the detected gastric cancer, which greatly improves the detection rate of gastric cancer in asymptomatic patients. According to statistics, about half of the asymptomatic gastric cancer patients have been confirmed as early gastric cancer by surgical pathology, and most of them have no lymph node metastasis; while 57% of symptomatic gastric cancer have already had lymph node metastasis. Therefore, the screening of natural population is a difficult and important task.
Outpatient screening is an important part of early diagnosis of gastric cancer, as anyone who comes to the clinic with relevant symptoms will be screened.
Early gastric cancer is characterized by symptoms such as hidden pain in the upper abdomen, bloating, loss of appetite, nausea and vomiting. These symptoms are not unique to early gastric cancer, so they are easily ignored as general gastric diseases, which is one of the reasons why patients are diagnosed too late. Therefore, it should be emphasized that men over 40 years old (relaxed to 35 years old for smokers and alcoholics) should be screened for any slight upper abdominal discomfort for the purpose of early detection and diagnosis. In addition, if the symptoms of dyspepsia are obvious and persist for a long time, and the symptoms do not improve significantly after clinical treatment, the possibility of gastric cancer should be considered. For those who have chronic atrophic gastritis, pernicious anemia, gastric polyps, residual stomach and benign gastric ulcer, they should be more alert to the evolution of gastric cancer. The detection rate of early gastric cancer by outpatient screening in China is 0.27%, which is lower than that in Japan (0.88%) and between that in Western Europe (0.37%) and the United States (0.1%). Nowadays, it is generally accepted that gastroscopy is the best screening method for early gastric cancer. For example, outpatient gastroscopy in Ruijin Hospital of Shanghai Second Medical University examined 26634 cases and detected 951 cases of gastric cancer, accounting for 3.57% of gastroscopy, including 72 cases of early gastric cancer, accounting for 7.6% of all gastric cancers. Due to the traditional habits of patients and the strict indications of gastroscopy in some hospitals, it is difficult to improve the detection rate of early gastric cancer.
The high-risk group of gastric cancer includes precancerous state and precancerous lesions.
The former refers to diseases with significantly higher risk of gastric cancer, such as chronic atrophic gastritis, gastric ulcer, gastric polyp, remnant stomach, and giant gastric mucosal crepitations. The latter mainly refers to pathological atypical hyperplasia of gastric mucosa. The detection rate of gastric cancer and early gastric cancer by high-risk group follow-up method is higher than that by census method and outpatient screening method. Nowadays, the natural course of gastric cancer is considered to be a slow process, which takes about 3-4 years to develop from the early stage to the progressive stage. Therefore, it is more appropriate to follow up and review gastroscopy every 6-12 months for high-risk groups. It is widely accepted that H. pylori infection is associated with gastric cancer. It has been demonstrated that the risk of gastric cancer is 3-6 times higher in H. pylori-infected individuals than in uninfected individuals. It is not clear whether treatment of H. pylori infection can prevent gastric cancer, but H. pylori-infected individuals with a family history of malignant gastric disease and clinical symptoms should be classified as a high-risk group for gastric cancer, and follow-up studies should be conducted, with interventional treatment if necessary.
Methods of detecting early gastric cancer
Laboratory tests
Gastric cancer markers: Many substances produced by gastric cancer cells can be detected in gastric juice, blood and other tissues, which can be used as gastric cancer markers for gastric cancer screening and screening, such as various enzymes and embryonic-derived markers.
Oncogenes.
It is generally believed that high expression of p2lras is associated with intestinal type gastric cancer, but it is highly expressed in dysplasia, intestinal metaplasia, and normal mucosa near the tumor, so it is thought that this gene plays a role in the earlier stages of gastric carcinogenesis. deletion mutations of APC gene are also mostly seen in the early stages of gastric cancer, and mostly occur in undifferentiated gastric cancer. In addition, p53 gene and CD44v6 gene expression were associated with gastric carcinogenesis and biological behavior of gastric cancer, and their expression increased sequentially in specimens with highly dysplastic gastric mucosa, early gastric cancer, and progressive gastric cancer. The evolution of gastric cancer is the result of multiple genetic alterations, and these above gastric cancer-related oncogenes are important for the genetic diagnosis of early gastric cancer, but the specificity is yet to be improved.
Gastric cancer monoclonal antibodies.
The application of monoclonal antibodies for the diagnosis of early gastric cancer is a major topic in current gastric cancer research. For example, monoclonal antibody MG7 was applied to 1090 patients and the positive rate was 41.8%.
Gastric cancer occult blood bead method.
The national census of more than 230,000 people showed that the positive rate of occult blood in gastric juice was 12%, 581 cases were diagnosed as esophageal cancer and gastric cancer, and the pathological examination of 70% of the patients was early and middle stage cancer. The specificity of this method is not high, but the method is simple and can be repeated several times or continuously and dynamically observed by the patient, so it is of great value in large-scale population screening.
Probabilistic computer model screening of gastric cancer: During the screening, according to the local risk factors of gastric cancer, meaningful factors are selected and a probabilistic mathematical model is established, and the data of each examinees are input into the computer, and after regression analysis, those with positive results are considered as high-risk group. This method can improve the detection rate if combined with the gastric cancer marker method.
Radiological examination
Although the majority of lesions can be detected, the malignant underdiagnosis rate is still high. Stomach imaging includes double contrast images, mucosal images, filling images, compression images and other examination methods. Through comparison, it can be found that the double contrast image and mucosal image can clearly show the lesion, and the compression image is especially important to show the lesion in the lower anterior wall of the stomach, and the four examination methods can complement each other to confirm and improve the detection rate of malignant lesions.
With the clinical application of duplex spiral CT and CT simulated gastroscopy, the sensitivity of imaging methods to detect early gastric cancer has been greatly improved. According to current statistics, the positive compliance rate of CT simulated gastroscopy for early gastric cancer diagnosis can reach over 70%, and the smallest mucosal lesion can be shown to be about 1cm in diameter. However, there is still a problem of high diagnostic cost, which is not suitable for screening.
Endoscopic examination method
Early gastric cancer does not have specific clinical symptoms, so patients over 40 years old with obvious indigestion symptoms or pre-cancerous lesions should be routinely examined by gastroscopy. Compared with imaging examination, endoscopy has significant advantages. It can directly observe the morphology of lesions, with wide field of view, strong resolution and high accuracy of biopsy.
Ultrasound endoscopy
It increases the diagnostic range of endoscopy, while shortening the distance between the ultrasound probe and the target organ, resulting in higher ultrasound resolution. The accuracy rate of ultrasound gastroscopy for early gastric cancer and progressive gastric cancer is 90%, and the accuracy rate for determining the type of cancer and the depth of infiltration is 70% to 80%. Ultrasound endoscopy also helps to detect whether there is local lymph node metastasis in early gastric cancer. In conclusion, early detection and early diagnosis of gastric cancer is the basis of early treatment and a key part of reducing the mortality rate of gastric cancer. Nowadays, with the continuous improvement of diagnostic techniques, there is every hope that clinical screening of early gastric cancer can be done well.