I. Overview of Stomach Cancer
Gastric cancer is one of the common malignant tumors in China, and its incidence rate ranks first among all kinds of tumors in China. The incidence rate of gastric cancer in China is the highest in Northwest China, followed by Northeast China and Inner Mongolia, followed by East China and the coast, and the lowest in South Central and Southwest China, and about 170,000 people die of gastric cancer every year, which is almost 1/4 of all malignant tumor deaths, and more than 20,000 new gastric cancer patients are produced every year. The causes of gastric cancer are unknown and may be related to various factors, such as lifestyle habits, diet, environmental factors, genetic quality, mental factors, etc. It is also related to chronic gastritis, gastric polyps, gastric mucosal anomalous hyperplasia and intestinal epithelial metaplasia, post-surgical residual stomach, and long-term Helicobacter pylori infection.
Gastric cancer can occur in any part of the stomach, but it is mostly found in the gastric sinus, especially on the side of the gastric malleolus. According to the infiltration depth of cancer tissue, it is divided into early gastric cancer and progressive gastric cancer. The early symptoms of gastric cancer are often not obvious, such as elusive upper abdominal discomfort, vague pain, belching, acidity, loss of appetite, mild anemia and other symptoms similar to gastroduodenal ulcer or chronic gastritis. In some patients, the pain is reduced or relieved after taking painkillers, anti-ulcer drugs or dietary modifications, and is therefore often ignored without further examination. As the disease progresses, the symptoms of stomach gradually become obvious, such as epigastric pain, loss of appetite, emaciation, weight loss and anemia. In the later stage, there are often metastasis, abdominal mass, enlarged left supraclavicular lymph node, black stool, ascites and severe malnutrition. Since gastric cancer is very common and dangerous in China, and the relevant researches believe that its causes are related to dietary habits and stomach diseases, it is very important to understand the basic knowledge about gastric cancer for its prevention and treatment.
Etiology
1.Environmental factors
The obvious difference of incidence rate between different countries and regions indicates that it is related to environmental factors, the most important of which is dietary factors. Excessive intake of salt, salted food with high salt content, smoked fish, and nitrosamines are related factors that induce gastric cancer, and moldy food contains more fungal toxins, and rice is covered with talcum powder after processing. In addition, there are also studies showing that gastric cancer is related to nutrient imbalance.
2.Genetic factors
The incidence of stomach cancer is higher in some families. The incidence rate of stomach cancer among relatives of patients with stomach cancer is four times higher than that of normal people. Some data show that stomach cancer occurs more often in people with blood type A than those with blood type O.
3.Immune factor
The incidence of stomach cancer is higher in people with low immune function.
4.Precancerous changes
Pre-cancerous changes refer to certain lesions with strong tendency of malignant transformation, which may develop into gastric cancer if left untreated. Pre-cancerous changes include pre-cancerous status and pre-cancerous lesions.
5.Stomach pre-cancerous state
(1) Chronic atrophic gastritis: there is a significant positive correlation between chronic atrophic gastritis and the incidence of gastric cancer.
(2) Pernicious anemia: gastric cancer occurs in 10% of patients with pernicious anemia, and the incidence of gastric cancer is 5-10 times that of normal population.
(3) Gastric polyps: Although adenomatous or villous polyps do not account for a high proportion of gastric polyps, the cancer rate is 15% to 40%. The cancer rate is higher for those with a diameter greater than 2 cm. Hyperplastic polyps are common, but the cancer rate is only 1%.
(4) Stomach remnant: the cancer that occurs in the stomach after surgery for benign lesions is called stomach remnant cancer. The incidence increases significantly after gastric surgery, especially from 10 years after surgery.
(5) Benign gastric ulcer: gastric ulcer itself is not a pre-cancerous state. Instead, the mucosa at the edge of the ulcer is prone to intestinal epithelial metaplasia and malignancy.
(6) Giant gastric mucosal fold disease: serum protein is lost through giant gastric mucosal fold, and there is clinical hypoproteinemia and swelling, and about 10% can become cancerous.
6.Pre-cancerous lesions of stomach
(1) Heteromorphic hyperplasia and interstitial lesions: the former is also called atypical hyperplasia, which is a reversible pathological cellular proliferation caused by chronic inflammation and is not carcinogenic in a few cases. Gastric interstitial lesions have more chances of carcinogenesis.
(2) Intestinal metaplasia: there are two types: small intestine type and large intestine type. Small intestine type has the characteristics of small intestine mucosa and is better differentiated. The large intestine type is similar to the large intestine mucosa and can be divided into two subtypes: type IIa, which can secrete non-sulfated mucin; type IIb, which can secrete sulfated mucin, and this type is closely related to the occurrence of gastric cancer.
Classification and staging of gastric cancer
1.Typing of gastric cancer
The site of gastric cancer can occur in any part of the stomach, more than half of them occur in the sinus, the lesser curvature and the anterior and posterior walls of the stomach, followed by the cardia, and relatively less in the body of the stomach.
2.Specific morphological classification
(1) Early gastric cancer: regardless of the extent, early lesions are limited to mucosa and submucosa. It can be divided into three types: elevated type, superficial type and depressed type. Among type II, there are three subtypes IIa, IIb and IIc. Each of the above types can have different combinations. For example, IIc+IIa, IIc+III, etc. Early gastric cancer with a diameter of 5-10mm is called small gastric cancer, while those with a diameter of <5mm are called micro gastric cancer. Both early gastric cancer and progressive gastric cancer can show upper gastrointestinal bleeding, often as black stool. Few early gastric cancers can show minor upper gastrointestinal bleeding symptoms, i.e. black stool or continuous positive occult blood in stool.
(2) Middle and advanced gastric cancer: also called progressive gastric cancer, the cancerous lesion invades the muscle layer or the whole layer, and often has metastasis.
(3) Mycosis fungoides type: it accounts for about 1/4 of advanced gastric cancer, the cancer is limited, mainly growing into the lumen, nodular or polyp-like, with rough surface like cauliflower and central erosion and ulcer, also called nodular mycosis fungoides type. If the cancer is discoid, with elevated edges and central ulcers, it is called discoid mycosis fungoides.
There is a swelling protruding from the posterior wall of the small curvature of the gastric sinus, slightly lobulated, with an uneven and granular surface, and vesicles are seen. The base of the swelling is slightly narrow and subtibial, and no obvious infiltration of the surrounding mucosa is seen
(4) Ulcerated type: It accounts for about 1/4 of advanced gastric cancer, and is divided into limited ulcerated type and infiltrated ulcerated type, the former is characterized by limited, disc-shaped cancer with central necrosis. The former is characterized by a limited, disc-shaped cancer with central necrosis, often with large and deep ulcers; the bottom of the ulcer is generally uneven, with raised edges in the shape of a dike or crater, and the cancer is infiltrated to a deeper level, often accompanied by bleeding and perforation. The infiltrative ulcer type is characterized by infiltrative growth of the cancer, often forming a mass with obvious infiltration to the periphery and deeper, with central necrosis forming an ulcer, often invading the plasma membrane or lymph node metastasis earlier.
(5) Infiltrative type: This type is also divided into two types, one is limited infiltrative type, in which the cancer tissue infiltrates all layers of gastric wall, mostly limited to the sinus, and the infiltrated gastric wall is thickened and hardened, and the wrinkled wall disappears, without obvious ulcers and nodules. If the infiltration is limited to a part of the stomach, it is called “limited infiltrative type”. The other type is diffuse infiltration type, also known as leathery stomach, in which the cancerous tissue expands under the mucosa and invades all layers with a wide range, making the stomach cavity smaller and the stomach wall thicker and stiffer, while the mucosa can still exist, and there can be congestion and edema without ulceration.
(6) Mixed type: two or more lesions of the above mentioned types co-exist at the same time.
(7) Multiple carcinomas: The cancerous tissues are multifocal and not connected with each other. For example, gastric cancer occurring on the basis of atrophic gastritis may belong to this type, and it is mostly found in the upper part of the stomach body.
4.Tissue typing.
1. According to the tissue structure, it can be divided into 4 types.
(1) Adenocarcinoma: including papillary adenocarcinoma, tubular adenocarcinoma and mucinous adenocarcinoma, which are classified into three types: highly differentiated, moderately differentiated and poorly differentiated according to their degree of differentiation.
(2) Undifferentiated carcinoma.
(3) Mucinous carcinoma.
(4) Special types of carcinoma: including adenosquamous carcinoma, squamous cell carcinoma, carcinoid carcinoma, etc.
2.There are two types according to histogenesis.
(1) Intestinal type: the cancer originates from the epithelium of intestinal glandular metaplasia, the cancer tissue is better differentiated, and the giant form is mostly myxoid.
(2) Gastric type: the cancer originates from the intrinsic mucosa of stomach, including undifferentiated cancer and mucinous cancer, the cancer tissue is poorly differentiated, and the giant form is mostly ulcerative and diffuse infiltrative.
V. Metastatic pathways
1.Direct dissemination: Infiltrating gastric cancer can develop along the mucosa or plasma membrane directly into the stomach wall, esophagus or duodenum. Once the cancer invades the plasma membrane, it is easy to infiltrate into the surrounding adjacent organs or tissues such as liver, pancreas, spleen, transverse colon, jejunum, diaphragm, greater omentum and abdominal wall. When cancer cells are shed, they can also be planted in the abdominal cavity, pelvic cavity, ovaries and rectal and bladder sockets.
2.Lymph node metastasis: it accounts for 70% of gastric cancer metastasis. Lower gastric cancer often metastasizes to lymph nodes such as subpyloric, subgastric and para-abdominal artery, while upper cancer often metastasizes to lymph nodes such as para-pancreatic, para-pancreatic and supragastric. Advanced cancer may metastasize to periaortic and supra-diaphragmatic lymph nodes. Since the abdominal lymph nodes are in direct communication with the thoracic duct, it may metastasize to the left supraclavicular lymph node.
3.Bloodstream metastasis: cancer cells can be found in peripheral blood of some patients, which can metastasize to liver through portal vein and reach lung, bone, kidney, brain, meninges, spleen, skin, etc.