What are Stomach Cancer Risk Factors?
Risk factors are the inherited or acquired factors that increase the chance of developing cancer in a person. Several epidemiological studies have suggested a number of genetic and environmental factors that may predispose to stomach cancer. A knowledge about them helps us to make necessary lifestyle choices.
Helicobacter pylori infection
Helicobacter pylori (H pylori) is a bacterium that generally infects the stomach and the duodenum and causes inflammation in these organs. An increased incidence of stomach cancers has been observed in individuals with the H pylori.
Chronic atrophic gastritis
It is a condition in which long-term inflammation of the stomach mucosa causes the loss of stomach mucosal cells and subsequent replacement with the intestinal and fibrous tissue. Various studies have shown that the patients with atrophic gastritis are at increased risk of developing stomach cancer.
Smoked or salted foods, low intake of fruits and vegetables, improperly prepared/stored food, foods rich in nitrates, and foods contaminated with aﬂatoxin are considered to elevate the risk of gastric cancer.
Regular exposure to heavy metals or harmful gases/fumes, especially those encountered in coal, metal, or rubber industry, has been found to increase the risk of stomach cancer.
Genetic Cancer Predisposition Syndromes
Some inherited cancer predisposition syndromes have been reported to be associated with a high incidence rate of stomach cancer.
Following are some examples:
- Hereditary diffuse stomach cancer (caused by mutation in the CDH1 gene);
- Lynch syndrome or hereditary non-polyposis colorectal cancer (HNPCC, generally caused by mutation in the MLH1 or MSH2 gene); \
- Familial adenomatous polyposis (FAP, caused by mutations in the APC gene);
- Li-Fraumeni syndrome (caused by mutation in the TP53 gene), and
- mutations in the breast cancer genes – BRCA1 or BRCA2.
Older age individuals especially men are at significantly higher risk of developing gastric cancer.
What are Intestinal and Diffuse types of Stomach Cancer?
First, we need to understand the difference between Intestinal and Diffuse Type of stomach cancer as the risk factors for both are different.
Now we will discuss the different subtypes of stomach cancer.
It may be broadly divided into two histopathological types, intestinal type and diffuse type.
First, we will compare the demographics or the population distribution of the two different variants of stomach cancer, that is, the intestinal and diffuse type.
As you can see in this figure, the intestinal variant is more common in the elderly, whereas, the diffuse type is more common in the young population.
Intestinal variant is more commonly seen in the males, whereas, diffuse variant is more common in the females.
Intestinal variant is common in endemic regions of Japan and south-east Asia, whereas, diffuse variant is more common in the developed countries.
To understand the location of these tumors and pathophysiology, first we have to know the normal anatomy of the stomach.
As you can see in this figure, the stomach lies in the upper part of the abdomen, called as epigastric region.
Gastroesophageal junction is the landmark where the esophagus joins the stomach. The most upper part of stomach is known as cardia. Below the cardia, liest the body of stomach.
The most distal part of the stomach, where it narrows down, is called as antrum.
And pylorus is the distance sphincter of the stomach, that controls the passage of gastic contents into the small intestine.
Now, after understanding the normal anatomy of the stomach, we will compare the distribution of the intestinal and the diffuse variant.
As you can see in this figure, the intestinal variant of stomach cancer is most commonly located either in the body or the pylorus.
Whereas, the diffuse variant maybe seen equally in any part of the stomach, that is, either cardia, body or pylorus.
What are the Risk Factors for Intestinal and Diffuse types of stomach cancer?
Now we move on to the risk factors for different subtypes of stomach cancer.
H. pylori infection is the most common cancer risk factor for the intestinal variant.
Whereas, the diffuse variant of stomach cancer is not associated with H. pylori infection.
Due to successful anti-H. pylori therapies available, the incidence of intestinal variant of stomach cancer is coming down.
On the other hand, the incidence of diffuse variant is increasing.
Dietary factors such as high salt or nitrate containing foods increase the incidence of intestinal variant of stomach cancer.
Also, increased intake of smoked or packaged or processed food increases the incidence of intestinal subtype.
Smoking is also a major risk factor for the intestinal subtype of stomach cancer, and the incidence increases with the intensity and duration of smoking.
Any long-standing benign ulcers of the stomach may also increase the risk of developing intestinal subtype of stomach cancer.
On the other hand, the most important risk factor for diffuse variant of stomach cancer is genetical or familial, that is, it may be inherited from other family members.
Stomach cancer may also be classified based on their location, that is, whether it is proximally located or distally located in the stomach.
Proximally located means either in the gastroesophageal junction or cardio, whereas, distally located means either in the body or pylorus of the stomach.
This figure shows the location of gastroesophageal junction tumors, that is, the tumors located in the lower part of the esophagus, gastroesophageal junction or the upper part of the stomach. The risk factors for all these three is almost similar.
Whereas, this figure shows the location of the tumors present in the body and pylorus. The risk factors for these are different.
The intestinal subtype of stomach cancer is less commonly seen in the GE junction and proximal part of stomach, and more commonly seen in the body and pylorus.
And the diffuse variant is seen equally in the cardia, body and the pylorus of stomach.
There has been a gradual increase in the incident of GE junction and proximal stomach tumors and a gradual decrease in the tumors in the body and pylorus, Let’s understand why.
H pylori infection is very commonly seen all over the world.
Long standing infection with H. pylori leads to damage to normal epithelium of stomach, which is called as atrophic gastritis, due to which there is a decrease in gastric acid production.
Due to chronic gastritis caused by H. pylori infection, there is a increased chance of cancers in the body and pylorus of the stomach.
On the other hand, atrophic gastritis caused by chronic H. pylori infection decreases the acid production by the stomach.
It reduces the chances of GERD, thereby reducing the chances of cancer in the GE junction and the cardiac region of the stomach.
But nowadays, due to successful anti-H. pylori therapy available, the cancers in the body and the pylorus have decreased, whereas, those in the GE junction and cardia have increased.