Stomach Cancer

Stomach cancer is a disease that arises when the cells lining the stomach multiply uncontrollably. The most common type is “adenocarcinoma”, which develops from the secretory cells of the inner surface of the stomach.

There are also less common stomach tumours, such as gastric lymphoma, gastrointestinal stromal tumour (GIST) and neuroendocrine tumour. However, the characteristics and treatment of these tumours differ from those of adenocarcinoma. The information on this page mainly describes gastric adenocarcinoma.

Stomach cancer may cause few or no symptoms in the early stages. Although complaints such as indigestion, bloating and stomach pain are mostly due to benign conditions, they need to be assessed if they persist for a long time or occur together with warning signs.

Some tumours that are at an early stage and lie only in the superficial layers of the stomach can be removed endoscopically. In more advanced disease that has not spread to other organs, surgery, chemotherapy and, nowadays, immunotherapy in selected patients may be used together. In disease that has spread to other parts of the body, treatment is personalised according to the molecular characteristics of the tumour [1–4].

What symptoms can stomach cancer cause?

Complaints that appear in the early stages may be confused with more common conditions such as gastritis, reflux or ulcers.

The following symptoms on their own do not mean stomach cancer; however, if they persist or are getting worse, a doctor’s assessment is needed:

• Long-lasting indigestion or heartburn
• Pain or discomfort in the upper abdomen
• Feeling full early after eating a small amount
• Marked bloating after meals
• Reduced appetite
• Unexplained weight loss
• Nausea or repeated vomiting
• Difficulty swallowing
• Weakness and tiring easily
• Anaemia
• Black, tar-like stools
• Blood in vomit

Particularly if there are findings such as unexplained weight loss, difficulty swallowing, anaemia, repeated vomiting or bleeding from the digestive tract, endoscopic assessment should not be delayed.

What causes stomach cancer?

There is no single cause of stomach cancer. Genetic characteristics, environmental factors, eating habits and changes that develop in the stomach lining over the years may play a role together.

The main risk factors are:

• Helicobacter pylori infection
• Smoking
• Frequent consumption of very salty and pickled foods
• Eating too little fresh vegetables and fruit
• Older age
• Stomach cancer in first-degree relatives
• Chronic atrophic gastritis and intestinal metaplasia
• Pernicious anaemia
• Certain tumours associated with the Epstein-Barr virus
• Certain previous stomach operations
• Certain inherited cancer syndromes

Having one of these risk factors does not mean that a person will definitely develop stomach cancer. Stomach cancer can also develop in people who have no obvious risk factors.

Why is Helicobacter pylori important?

Helicobacter pylori is a bacterium that can cause long-term inflammation of the stomach lining. It is recognised by the World Health Organization as an important carcinogen with regard to stomach cancer.

Eradicating the infection with appropriate antibiotics can reduce the risk of stomach cancer, particularly when it is done before cancer develops. However, in people who have already developed advanced changes in the stomach lining, treating the bacterium alone may not be enough and endoscopic follow-up may be needed.

In people who have been treated for Helicobacter pylori, it is important to confirm with an appropriate test that the bacterium has actually been cleared.

Can stomach cancer be inherited?

Most stomach cancers are not inherited. Nevertheless, some families may have a genetic predisposition.

In particular, in situations such as

• Stomach cancer in more than one person in the family
• Stomach cancer occurring at a young age
• A family history of diffuse-type stomach cancer
• Frequent occurrence of breast, bowel or certain other cancers together with stomach cancer

genetic counselling may be considered.

In hereditary diffuse gastric cancer syndrome, the CDH1 gene and, less often, the CTNNA1 gene are important. Because the decision on genetic testing may affect the follow-up not only of the patient but also of family members, it should be made with genetic counselling.

Endoscopy and biopsy

The main method for diagnosing stomach cancer is upper gastrointestinal endoscopy. In this procedure, also called gastroscopy, a thin device with a camera is passed through the mouth to examine the oesophagus, the stomach and the first part of the duodenum.

Several small tissue samples, that is, biopsies, are taken from suspicious areas. The definitive diagnosis is made by pathological examination.

In the pathology report,

• The type of tumour
• The degree of differentiation of the cells
• Certain special microscopic features
• Where necessary, biological markers that guide treatment

may be assessed.

If a suspicious area is seen at endoscopy but the first biopsy result does not show cancer, the endoscopy and biopsies may need to be repeated if clinical suspicion remains.

Why is staging important?

Staging is the process of determining

• How far the disease has advanced in the stomach wall
• Whether it has reached the surrounding lymph nodes
• Whether it has spread to the liver, lungs, the lining of the abdomen or other organs

in other words, how far the disease extends.

Whether treatment begins with endoscopy, immediate surgery, drug treatment before surgery or systemic treatment is determined by the stage.

Which imaging methods are used?

Once the diagnosis has been confirmed, a computed tomography (CT) scan of the chest and abdomen is usually performed.

In selected patients, the following examinations may also be used:

• Endoscopic ultrasound: Particularly in tumours thought to be at an early stage, it can assess the depth of the tumour in the stomach wall and the nearby lymph nodes.
• PET-CT: May be useful in some patients to assess suspected spread to other organs.
• MRI: May be requested particularly if there is a suspicious area in the liver, or in certain special situations.

PET-CT does not have the same sensitivity for every type of stomach cancer. In particular, some diffuse-type tumours, mucin-containing tumours or tumours with low metabolic activity may not show up clearly on PET-CT. For this reason, a normal PET-CT does not on its own prove that there is no disease.

What is diagnostic laparoscopy?

Stomach cancer can spread to the lining of the abdomen in very small deposits, and these deposits may not be visible on computed tomography.

In patients whose tumour appears removable by surgery but who are at risk of spread to the lining of the abdomen, a diagnostic laparoscopy may be performed before major surgery or before treatment prior to surgery. In this procedure, a camera is introduced into the abdomen through small incisions and the inside of the abdomen is assessed directly.

During the procedure, fluid can be introduced into the abdomen and a sample taken. This examination, called “peritoneal washing cytology”, looks for cancer cells that cannot be seen with the eye. The result may change the treatment plan [1,2].

Why are molecular and biological tests carried out?

In advanced gastric adenocarcinoma or gastric adenocarcinoma that has spread to other organs, the tumour tissue is tested for characteristics that may influence the choice of treatment.

The main tests are:

• HER2: In HER2-positive tumours, medicines that target HER2 can be used.
• PD-L1: Helps to assess the likelihood of benefiting from immunotherapy.
• MSI or MMR: Shows a DNA repair defect. Tumours that are MSI-high or MMR-deficient may be more sensitive to immunotherapy.
• CLDN18.2: In suitable patients, may help with the use of medicines that target this protein.
• Comprehensive molecular profiling: May be carried out in selected patients to look for rare but treatable genetic changes.

Not all of these tests are needed at the same stage in every patient. The scope of testing is determined by the stage of the disease, the amount of tissue available and the planned treatment [3,4].

Tumour markers measured in the blood, such as CEA or CA 19-9, cannot establish a diagnosis of stomach cancer on their own. If they are raised at the outset in some patients, they can help in assessing the response to treatment and the course of the disease.

The treatment of stomach cancer should be planned by a multidisciplinary tumour board. This team may include a general surgeon, a gastroenterological surgeon, a medical oncologist, a radiation oncologist, a gastroenterologist, a radiologist, a pathologist and, when needed, a nutrition specialist.

In the treatment plan, the following characteristics are assessed together:

• The stage of the disease
• The location of the tumour in the stomach
• Pathological and molecular characteristics
• The patient’s age and general state of health
• Nutritional status
• Coexisting conditions
• The patient’s preferences

Can very early-stage stomach cancer be treated by endoscopy?

Some early-stage tumours that lie only in the superficial layers of the stomach and have a very low risk of spreading to the lymph nodes can be removed using a method called endoscopic submucosal dissection.

No incision is made in the abdomen in this procedure. The tumour is removed in one piece through the endoscope, together with a safe margin of surrounding tissue.

In the pathological examination of the removed tissue,

• The depth of the tumour
• The resection margins
• Involvement of blood vessels or lymphatic channels
• Cellular characteristics

are assessed. If the result is not favourable, surgical treatment that also includes the lymph nodes may be needed.

Endoscopic treatment cannot be applied to every early stomach cancer. It should be carried out in centres with experienced endoscopy and pathology teams [2,4].

How is stomach cancer surgery performed?

The aim of the operation is to remove the tumour with adequate safe margins, together with the regional lymph nodes to which the disease may spread.

Depending on the location of the tumour,

• Subtotal or distal gastrectomy: Removal of the lower part of the stomach
• Total gastrectomy: Removal of the whole stomach
• Proximal gastrectomy: Removal of the upper part of the stomach in selected early-stage tumours

may be performed.

Not every stomach cancer requires removal of the whole stomach. If the tumour can be removed with safe margins, preserving part of the stomach can be beneficial for nutrition and quality of life.

Why are lymph nodes removed?

Stomach cancer can spread through the lymphatic channels. The systematic removal of the appropriate lymph nodes around the stomach during the operation is called lymph node dissection.

In localised stomach cancer suitable for surgery, D2 lymph node dissection in experienced centres is the current standard approach. This procedure allows accurate staging and contributes to regional control of the disease [1,2].

If the tumour has grown directly into neighbouring organs such as the spleen or pancreas, these organs may be removed while keeping the tumour intact.

Can stomach cancer surgery be performed as keyhole surgery?

In suitable patients, gastrectomy can be performed laparoscopically or robotically. Particularly in experienced centres, minimally invasive surgery may offer

• Smaller incisions
• Less pain after the operation
• Earlier mobilisation and eating
• A shorter hospital stay
• Fewer wound complications

among other advantages.

However, the most important goal is not whether the operation is done by keyhole or open surgery, but that the tumour is removed with safe margins and an adequate lymph node dissection is carried out. Open surgery may be preferred for advanced tumours, in patients with involvement of neighbouring organs, or where technical safety cannot be ensured.

Why is chemotherapy given before the operation?

In locally advanced but resectable stomach cancer, many patients are given part of their chemotherapy before the operation and the rest after it. This is called “perioperative treatment”.

The aim is:

• To shrink the tumour
• To treat at an early stage cancer cells that cannot be detected on imaging
• To increase the likelihood that the tumour can be removed completely
• To reduce the risk of the disease returning

In patients whose general state of health allows it, the chemotherapy regimen called FLOT is one of the important standard options in perioperative treatment. The survival benefit of this approach was shown in the FLOT4 trial [5].

Not every patient may be able to tolerate FLOT treatment. Milder treatment regimens may be chosen, taking into account age, heart and kidney function, nutritional status and capacity for daily activities.

Can immunotherapy be added to treatment before surgery?

In the phase III trial called MATTERHORN, adding the immunotherapy durvalumab to FLOT chemotherapy prolonged event-free survival in resectable cancers of the stomach and the gastro-oesophageal junction [6].

On the basis of these results, perioperative treatment combining durvalumab with FLOT has been approved in some countries. However, applicability depends on

• The stage of the disease
• The patient’s general condition
• The licensing and reimbursement conditions for the medicine in the country
• The decision of the oncology tumour board

and may vary accordingly.

For this reason, it cannot be said that every patient with resectable stomach cancer must receive immunotherapy. The choice of treatment should be individualised, taking into account current guidelines and conditions in the country.

Is additional treatment needed for patients who have surgery first?

In some patients, chemotherapy may be recommended after stomach cancer has been removed by surgery, depending on the pathology result. Chemotherapy after the operation may be considered particularly in patients with stage II–III disease who have had an adequate D2 lymph node dissection and did not receive chemotherapy before the operation.

In cases of tumour at the resection margin, inadequate lymph node dissection or certain high-risk disease, radiotherapy combined with chemotherapy may be considered in selected patients. Radiotherapy is not used routinely in every patient with stomach cancer [1,2].

How is advanced stomach cancer treated?

If the disease has spread to other organs or to the lining of the abdomen, the basis of treatment is systemic medicines.

Treatment can be personalised according to the biological characteristics of the tumour:

• In HER2-positive tumours: Medicines that target HER2 can be added to chemotherapy.
• In PD-L1-positive tumours or tumours with suitable characteristics: Immunotherapy can be used together with chemotherapy.
• In MSI-high or MMR-deficient tumours: Immunotherapy can bring marked benefit.
• In HER2-negative and CLDN18.2-positive tumours: Zolbetuximab, which targets CLDN18.2, can be used together with chemotherapy in suitable patients.
• In disease that progresses after treatment: Different chemotherapy, targeted therapy or immunotherapy options can be considered according to previous treatments and the characteristics of the tumour [3,4].

These treatments may not be approved or reimbursed at the same time in every country. The most suitable option should be determined by a medical oncology assessment.

Is surgery performed at an advanced stage?

In stomach cancer that has spread to other organs, routine removal of the stomach does not bring a survival benefit in most patients. For this reason, surgery is not the standard first treatment.

However, if there is:

• Bleeding that cannot be controlled
• Obstruction of the stomach outlet
• Perforation of the stomach
• A condition that prevents eating

surgery or an endoscopic procedure may be needed.

In some patients with limited metastases who respond very well to treatment, surgery may be considered in highly experienced centres following a decision by the multidisciplinary tumour board. This approach is not standard and cannot be applied to every patient.

How long is the hospital stay after the operation?

The length of the hospital stay varies according to the extent of the operation, whether it is done by open or keyhole surgery, the patient’s general condition and the course of recovery. After an uncomplicated operation, most patients may need a hospital stay of about 3–10 days.

As part of current enhanced recovery programmes,

• Effective pain control
• Getting up and walking early
• Breathing exercises
• Early eating in suitable patients
• Measures to prevent blood clots in the veins and lungs

are planned together.

How does eating change after the operation?

When part or all of the stomach is removed, the amount of food that can be eaten at one time decreases. For this reason,

• Eating small portions
• Having 5–6 small meals a day
• Eating slowly and chewing food well
• Not drinking too much fluid with meals
• Eating enough protein
• Limiting foods high in sugar

may be helpful.

Every patient’s nutritional needs are different. Getting support from a dietitian, starting before the operation, helps to reduce weight and muscle loss.

What is dumping syndrome?

After part or all of the stomach has been removed, food passing into the small intestine faster than normal can lead to dumping syndrome.

Shortly after a meal,

• Palpitations
• Sweating
• Abdominal pain
• Bloating
• Nausea
• Diarrhoea
• Weakness or dizziness

may occur.

In some patients, trembling, sweating and weakness due to a fall in blood sugar may develop 1–3 hours after a meal.

Small, frequent meals, cutting down on simple sugars and taking fluids separately from meals can reduce the symptoms. If the complaints persist, support from a dietitian and a doctor should be sought.

Are vitamin and mineral supplements needed?

After a total gastrectomy, B12 supplementation is needed because the absorption of vitamin B12 from food is impaired.

Vitamin B12 deficiency can also develop in some patients after a subtotal gastrectomy. In addition, deficiencies of:

• Iron
• Folic acid
• Vitamin D
• Calcium
• Protein may occur.

For this reason, weight, muscle strength, blood count and vitamin and mineral levels should be monitored regularly. Supplements are adjusted individually according to blood results and the operation performed.

How is follow-up carried out after treatment?

The aim of follow-up is:

• To assess whether the disease has returned
• To manage the side effects of treatment
• To monitor weight and nutritional status
• To detect vitamin and mineral deficiencies
• To support the patient’s daily life and psychological well-being

The follow-up programme may include examinations, blood tests and, depending on the stage of the disease, computed tomography. Endoscopy may be performed in patients in whom part of the stomach has been preserved or where there is a specific clinical reason.

The frequency of follow-up is determined by the stage of the disease, the treatment given and the patient’s complaints. The same follow-up programme is not applied to every patient.

If there is new weight loss, persistent abdominal pain, difficulty swallowing, repeated vomiting, black stools or inability to eat, the healthcare team should be contacted without waiting for the planned appointment.

1. Lordick F, Carneiro F, Cascinu S, et al. Gastric Cancer: ESMO Clinical Practice Guideline for Diagnosis, Treatment and Follow-up. Annals of Oncology. 2022;33(10):1005–1020. Updates: ESMO Living Guideline. https://www.esmo.org/guidelines/living-guidelines/esmo-living-guideline-gastric-cancer
2. Shitara K, Ajani JA, Moehler M, et al. Pan-Asian Adapted ESMO Clinical Practice Guidelines for the Diagnosis, Treatment and Follow-up of Patients with Gastric Cancer. ESMO Open. 2024;9(2):102226. https://www.esmoopen.com/article/S2059-7029(23)01467-9/fulltext
3. Ajani JA, D’Amico TA, Bentrem DJ, et al. Gastric Cancer, Version 2.2025, NCCN Clinical Practice Guidelines in Oncology. JNCCN. 2025;23(5):169–191. https://pubmed.ncbi.nlm.nih.gov/40341199/
4. Development Working Group for the Korean Practice Guideline for Gastric Cancer 2024 Task Force Team. Korean Practice Guidelines for Gastric Cancer 2024: An Evidence-Based, Multidisciplinary Approach. Journal of Gastric Cancer. 2025;25(1):5–114. https://pmc.ncbi.nlm.nih.gov/articles/PMC11739648/
5. Al-Batran SE, Homann N, Pauligk C, et al. Perioperative Chemotherapy with FLOT versus ECF/ECX for Locally Advanced, Resectable Gastric or Gastro-oesophageal Junction Adenocarcinoma: FLOT4. The Lancet. 2019;393:1948–1957. https://pubmed.ncbi.nlm.nih.gov/30982686/
6. Janjigian YY, Al-Batran SE, Wainberg ZA, et al. Perioperative Durvalumab in Gastric and Gastroesophageal Junction Cancer: MATTERHORN. New England Journal of Medicine. 2025. https://pubmed.ncbi.nlm.nih.gov/40454643/