Stomach cancer, also known as gastric cancer, is the cancer of the stomach and can form in any part of your stomach. According to the Global Cancer Observatory 2022 data report, stomach cancer ranks fifth as the most common cancer type with around 968000 cases reported annually all around the globe. It also ranks 5^th as the most deadly cancer with around 660000 deaths reported globally in 2022. The high mortality rate highlights the importance of understanding what stomach cancer is, what its symptoms are, and what causes and risk factors are involved so that this disease can be caught early or even prevented.

What is the stomach and its function?

The stomach is a muscular organ which is responsible for the digestion of food. It is a part of the gastrointestinal (GI) tract and is responsible for producing enzymes (proteins that help speed up chemical reactions in our bodies) and acids (released from glands in the stomach wall). Additionally, the muscles in the stomach continuously contract and relax to move and mix the food. The enzymes and acids, alongside the movement produced by the muscles in the stomach, help digest the food, breaking it up into smaller bits, so that it can pass into the small intestine.

What is stomach cancer?

Stomach cancer is characterised by the uncontrollable replication and growth of cells in the stomach.  Around 95% of stomach cancers start in the stomach lining. If not caught at an earlier stage and treated, it can develop into a mass called a tumour, and grow deeper into the stomach walls. It can then start spreading (metastasis) into other organs. The most common sites of metastasis of stomach cancer are the liver (in 48% of stomach cancer patients), the peritoneum (the lining of the inside of your abdomen and pelvis) (32%), the lungs (15%), and bones (12%).¹

While stomach cancer is the 5^th most common cancer in the world, according to Cancer Research UK, it ranks as the 17^th in the UK with around 6500 new stomach cancer cases every year. Additionally, approximately half of stomach cancer cases are diagnosed in individuals aged 75 or older.

What are the types of stomach cancer?

There are several different types of stomach cancer:

• Adenocarcinoma – the most common type of stomach cancer. Around 95% of stomach cancers are adenocarcinomas. It develops in the mucus-producing cells in the inner lining of the stomach. Adenocarcinomas can be classified as gastric cardia cancer (which develops in the upper part of your stomach, close to your oesophagus food pipe) and non-cardia stomach cancer (which can develop in any part of your stomach). Adenocarcinomas can also be categorised as intestinal, diffused or mixed subtypes depending on the appearance of the cells.²
  • Intestinal subtype cancer cells look similar to healthy stomach cells, while diffuse-type cells look different. 
  • Diffuse subtype cancer is a more aggressive form, which spreads more quickly. 
  • The mixed subtype is a mixture of both subtypes and tends to be the most aggressive.³

• Gastrointestinal stromal tumours (GISTs) – GIST is a type of soft tissue sarcoma. It starts in the nerve cells, which are situated in the wall of your stomach.
• Gastrointestinal neuroendocrine tumours – these tumours form in neuroendocrine cells (cells like nerve cells, which also produce hormones like endocrine cells) present in the lining of the stomach.
• Gastroesophageal junction adenocarcinoma – is a type of cancer that develops in the part where the oesophagus(food pipe) and stomach meet.
• Primary gastric lymphoma – this is a type of non-Hodgkin lymphoma that starts in the stomach. The majority of gastric lymphomas are either mucosa-associated lymphoid tissue (MALT) gastric lymphoma or diffuse large B-cell lymphoma. 

What are the symptoms of stomach cancer?

Early stages of stomach cancer are often asymptomatic, making it hard to diagnose. However, some early-stage symptoms to look out for include:

• Indigestion
• Stomach discomfort
• Feeling bloated after eating
• Mild nausea
• Loss of appetite
• Heartburn

In the later stages of stomach cancer, additional symptoms develop, such as:

• Blood in the stool 
• Vomiting 
• Weight loss for no apparent reason 
• Stomach pain 
• Jaundice (yellowing of the eyes and skin) 
• Ascites (build-up of fluid in the abdomen) 
• Trouble swallowing (dysphagia)

However, it is worth noting that these symptoms can be a part of other conditions. It is important to see your doctor if you have any of these symptoms to form a correct diagnosis.

What causes stomach cancer?

Stomach cancer is often caused by genetic mutations (changes in your DNA sequence) in the stomach cells. DNA is a genetic code that contains all the instructions for correct cell reproduction, development and function. Even a small change in your DNA can lead to great consequences. In the case of cancer, it can help the cells to grow uncontrollably and fast into a tumour.

What are the risk factors?

It is estimated that around 54% of cases of stomach cancers are preventable. Factors that have been identified to increase the risk of stomach cancer include:

• Genetics – some inherited mutations in genes, such as GSTM1 or CDH1 gene, can increase the risk of stomach cancer. However, it only accounts for 1-10% of the total cases.^2,4 
• Gastric ulcers – an open sore which develops in the lining of your stomach. It is estimated that in people with gastric ulcers, stomach cancer occurs twice as commonly as compared to people without any gastric ulcers.
• Helicobacter pylori – H. pylori is a bacterium considered to be the main risk factor for stomach cancer.² Infection with H. pylori is predicted to occur in more than one-half of the world population and it has been classified as a class I carcinogen (a substance, an organism or an agent that can cause cancer).⁴ This bacteria can cause acute gastritis and up to 80% of gastric ulcers are caused by this bacteria.² Treating H. pylori infection in people with gastric ulcers leads to fewer cases of stomach cancer.⁴ What’s more is that around 90% of cases of the non-cardia subtype are linked to H.pylori.²
• Epstein Barr virus (EBV) – EBV has also been shown to affect stomach cancer development in around 10% of cases.⁴ 
• Gastroesophageal reflux disease (GERD) – GERD is a disease that causes stomach acid to flow from the stomach into the oesophagus. GERD has been associated with the cardia gastric cancer type, which affects the top part of the stomach close to the oesophagus.
• Smoking – smoking has also been shown to increase the risk of gastric cancer. It is estimated that around 11% of stomach cancer cases globally and 17% of cases in Europe are associated with smoking.
• Alcohol use – alcohol use is another risk factor for stomach cancer. However, the amount of alcohol use associated with stomach cancers is a bit unclear. Some studies have reported an increase in cases of both moderate and heavy consumption of alcohol while other studies only reported an increase in heavy consumption.
• Diet – diets high in salt and saturated fats have also been associated with an increased risk of stomach cancers. This kind of diet can contribute to the inflammation of the stomach, which promotes the development of cancer.⁵ On the other hand, diets high in fruits and vegetables have been shown to decrease the risk of stomach cancer.²
• Obesity – Obesity is also associated with stomach cancer, and the association increases with increasing BMI. Obesity may cause inflammation of the stomach lining.
• Socioeconomic status – higher rates of stomach cancer have been associated with groups of low socioeconomic status. It is thought that higher rates of H. pylori infection and/or lower access to fresh food, fruits and vegetables may be the cause of this.

How is stomach cancer diagnosed?

As with most appointments with your doctor, firstly a medical history will be taken and a physical exam will be performed, which may include feeling for a mass in your stomach. A blood test might also be done. This is to check for signs of anaemia, as this could indicate bleeding in the stomach.

There are several tests and procedures that may help with diagnosing stomach cancer, which include:

• Upper endoscopy – during this procedure, your doctor looks inside the oesophagus, stomach, and duodenum (first part of the small intestine) to check for anything abnormal. An endoscope, a thin, lighted tube, is passed through your mouth and down the throat into your oesophagus. It may also be used to remove a small sample of cells or tissue (biopsy), which can then be checked for signs of cancer. It can also be used to test for H. pylori infection.
• Barium swallow –this procedure includes drinking a liquid containing barium. This liquid coats your stomach and oesophagus, making it visible in X-rays. Then you will have a series of X-rays taken.
• CT scan – during this test many detailed pictures are taken from different angles. A dye may need to be injected into your vein or swallowed to help your organs or tissues be clearer in the pictures.

Summary

Stomach cancer is a serious condition that can affect any part of the stomach, caused by genetic mutations in stomach cells, which can lead to the rapid growth of them and eventually form a tumour. There are several risk factors associated with stomach cancers, which include H.pylori and EBV infections, gastric ulcers, GERD and others. It is important to know these risk factors as many cases of stomach cancer are thought to be preventable.