Stomach Cancer (Gastric Cancer): A Guide for Patients and Caregivers
What Is the Stomach and What Does It Do?
The stomach is a muscular, hollow organ located in the upper part of the abdomen, just below the ribs. It plays an important role in digestion.
After food is swallowed, the stomach:
- Temporarily stores food
- Uses acid and digestive enzymes to break food down
- Mixes food into a semi-liquid form
- Releases food gradually into the small intestine for further digestion
The inner lining of the stomach contains specialised cells that produce acid, mucus, and enzymes. Most stomach cancers begin in this inner lining.
What Is Stomach (Gastric) Cancer?
Stomach cancer, also called gastric cancer, develops when abnormal cells in the lining of the stomach grow uncontrollably and form a tumour. In most cases, stomach cancer develops slowly over many years.
Types of Stomach Cancer
Several types of cancer can occur in the stomach:
- Adenocarcinoma
The most common type. It begins in the gland-forming cells of the stomach lining and accounts for the majority of stomach cancers.
- Lymphoma
A cancer of immune cells that can develop in lymph tissue within the stomach.
- Gastrointestinal stromal tumours (GISTs)
Rare tumours arising from the muscle or connective tissue of the stomach wall.
- Neuroendocrine tumours
Rare cancers arising from hormone-producing cells.
When doctors talk about stomach cancer, they are usually referring to adenocarcinoma.
Causes and Risk Factors for Stomach Cancer
Stomach cancer usually develops due to a combination of environmental, lifestyle, and biological factors.
Common risk factors include:
- Infection with Helicobacter pylori (H. pylori)
- Long-standing inflammation of the stomach lining
- Smoking
- Diets high in salty, smoked, or processed foods
- Low intake of fruits and vegetables
- Excessive alcohol use
- Increasing age
Having risk factors does not mean a person will definitely develop stomach cancer, but it increases the likelihood.
Genetic and Inherited Risk
Most stomach cancers are not inherited, but a small proportion are linked to inherited genetic conditions. A genetic cause may be suspected when stomach cancer:
- Occurs at a young age
- Affects multiple family members
- Is associated with other cancers in the family
Important inherited conditions linked to stomach cancer include:
- Hereditary Diffuse Gastric Cancer
Caused by changes in the CDH1 or CTNNA1 genes. This condition increases the risk of a diffuse type of stomach cancer that can be difficult to detect early.
- Lynch Syndrome
Caused by changes in DNA repair genes such as MLH1, MSH2, MSH6, or PMS2. It increases the risk of several cancers, including stomach cancer.
- Familial Adenomatous Polyposis (FAP)
Related to changes in the APC gene and mainly associated with bowel cancer, but stomach cancer risk may also be increased.
- Peutz–Jeghers Syndrome
Caused by changes in the STK11 gene and associated with cancers of the digestive tract.
If inherited risk is suspected, genetic counselling and testing using a blood or saliva sample may be recommended. This can help guide screening and preventive strategies for patients and their family members.
Symptoms of Stomach Cancer
Early stomach cancer often causes no symptoms, which is why it is frequently diagnosed at a later stage.
Possible symptoms include:
- Persistent indigestion or heartburn
- Upper abdominal pain or discomfort
- Feeling full after eating small amounts
- Loss of appetite
- Unexplained weight loss
- Nausea or vomiting
- Vomiting blood or passing black stools
- Fatigue, sometimes due to low blood counts
These symptoms can also occur with non-cancerous conditions, but persistent or worsening symptoms should always be evaluated.
How Is Stomach Cancer Diagnosed?
Endoscopy
An upper gastrointestinal endoscopy is the most important test for diagnosing stomach cancer.
- A thin flexible tube with a camera is passed through the mouth into the stomach
- The doctor can directly examine the stomach lining
- Suspicious areas can be biopsied during the same procedure
Endoscopy is usually done with sedation, so patients are comfortable.
Biopsy
A biopsy involves taking small samples of tissue from the abnormal area.
A biopsy is essential because it:
- Confirms the diagnosis
- Identifies the exact type of cancer
- Provides tissue for molecular and biomarker testing
Without a biopsy, stomach cancer cannot be definitively diagnosed.
Imaging Tests
- CT scans of the chest, abdomen, and pelvis help assess tumour size, lymph node involvement, and spread to other organs
- PET scans may be used in selected cases to detect cancer spread that is not clearly visible on CT scans
What Does Stomach Cancer Look Like Under the Microscope?
Most stomach cancers are adenocarcinomas. When examined under a microscope:
- Normal stomach cells appear organised and structured
- Cancer cells appear abnormal, crowded, and disorganised
- Some cancers form distorted gland-like structures
- Others spread as scattered cells and may contain mucus, giving them a “signet-ring” appearance
This microscopic examination confirms cancer and provides information about how aggressive it may be.
Molecular and Biomarker Testing in Stomach Cancer
After diagnosis, tumour tissue is tested to guide personalised treatment.
How Are These Tests Done?
- Immunohistochemistry (IHC): Special stains applied to tumour tissue to detect specific proteins
- Additional molecular tests: Used when needed to confirm results
- Next-generation sequencing (NGS): Analyses multiple genes at once to identify treatment-relevant changes
Important Biomarkers
- HER2: Identifies patients who may benefit from HER2-targeted therapy
- PD-L1: Helps guide the use of immunotherapy
- MMR / MSI status: Tumours with defective DNA repair often respond well to immunotherapy
- Claudin 18.2: Identifies patients who may benefit from newer targeted treatments
Staging of Stomach Cancer
Staging describes how far the cancer has spread and plays a key role in deciding the best treatment approach.
Stomach cancer is broadly grouped into:
- Early stage: Cancer confined to the stomach lining
- Locally advanced: Cancer has grown deeper into the stomach wall and/or spread to nearby lymph nodes
- Metastatic (stage IV): Cancer has spread to distant organs such as the liver, lungs, or the lining of the abdomen
Staging is based on information from endoscopy, biopsies, imaging tests, and sometimes surgical assessment.
The Role of Diagnostic Laparoscopy in Accurate Staging
In some patients with stage II or stage III (locally advanced) stomach cancer, doctors may recommend a diagnostic laparoscopy as part of the staging process.
Diagnostic laparoscopy is a minimally invasive procedure performed under general anaesthesia. Through a few very small incisions in the abdomen, a thin camera is inserted to allow the surgeon to look directly inside the abdominal cavity.
This procedure helps to:
- Detect small areas of cancer spread on the lining of the abdomen that may not be visible on CT or PET scans
- Identify very early metastatic disease that can change the treatment plan
- Avoid major surgery that may not be beneficial if hidden spread is found
- Confirm whether the cancer is truly suitable for surgery with curative intent
During laparoscopy, the surgeon may also take washings or small biopsies to check for cancer cells.
By improving the accuracy of staging, diagnostic laparoscopy helps ensure that patients with locally advanced stomach cancer receive the most appropriate treatment from the outset.
Treatment of Stomach Cancer Based on Stage
Early and Locally Advanced Stomach Cancer
Surgery
Surgery is the main treatment with curative intent.
- Part or all of the stomach may be removed, depending on tumour location
- Nearby lymph nodes are removed at the same time
Lymph node removal is essential because stomach cancer commonly spreads through lymph channels.
A D2 lymph node dissection removes lymph nodes close to the stomach as well as those along major blood vessels. When performed by experienced surgeons, this approach improves staging accuracy and reduces the risk of cancer being left behind.
Peri-operative Treatment (Before and After Surgery)
For many patients, treatment is given both before and after surgery.
- Combination chemotherapy is commonly used
- A widely used regimen is FLOT or modified FLOT
- In modern practice, chemotherapy is often combined with immunotherapy such as durvalumab
This approach improves cure rates by shrinking the tumour and reducing the risk of recurrence.
If Treatment Before Surgery Is Not Possible
If pre-operative treatment cannot be given, post-operative (adjuvant) chemotherapy may be recommended.
Metastatic (Stage IV) Stomach Cancer
When stomach cancer has spread, treatment focuses on:
- Controlling disease
- Reducing symptoms
- Prolonging survival
- Maintaining quality of life
Chemotherapy
Commonly used drugs and combinations include:
- Oxaliplatin-based regimens such as FOLFOX or CAPOX
- Carboplatin with paclitaxel
- Irinotecan-based treatments in later lines
Immunotherapy
Immunotherapy helps the immune system recognise and attack cancer cells.
- It is often more effective in tumours with higher PD-L1 expression or MSI-high/MMR-deficient cancers
- It may still be used in selected patients even if PD-L1 is low
Common immunotherapy drugs include:
- Nivolumab
- Pembrolizumab
- Tislelizumab
- Toripalimab
Targeted Therapies
HER2-positive disease
- Treated with trastuzumab combined with chemotherapy
- Trastuzumab deruxtecan (T-DXd) is used after progression
Some patients have both HER2 positivity and PD-L1 expression, and treatment may combine chemotherapy, HER2-targeted therapy, and immunotherapy.
Anti-angiogenic therapy
- Ramucirumab, often combined with paclitaxel, is commonly used after first-line treatment.
Claudin 18.2–Targeted Treatments
Claudin 18.2 is a protein found on some stomach cancer cells.
- Zolbetuximab, a monoclonal antibody, can be combined with chemotherapy in Claudin 18.2-positive disease
- Antibody-drug conjugates (ADCs) targeting Claudin 18.2 are emerging treatments that deliver chemotherapy directly to cancer cells
- CAR-T cell therapies targeting Claudin 18.2 are evolving options available in specialised centres and clinical trials
Living With Stomach Cancer
Supportive care is a vital part of treatment and includes:
- Nutritional support
- Management of treatment side effects
- Pain and symptom control
- Emotional and psychological support
- Support for caregivers and families
Many patients continue to live meaningful lives while receiving treatment.
Key Takeaways
- Endoscopy with biopsy is essential for diagnosis
- Molecular testing allows personalised treatment
- Accurate staging, including diagnostic laparoscopy when appropriate, guides the best treatment plan
- Surgery combined with modern systemic therapy offers the best chance of cure in earlier stages
- Advanced stomach cancer can still be effectively treated
- New targeted and immune-based treatments continue to improve outcomes
