Stomach cancer, also known as gastric cancer, develops when cells in the lining of the stomach begin to grow and divide abnormally. Because early stomach cancer often causes few or no noticeable symptoms, it is sometimes diagnosed only once it has progressed — which is part of why understanding the condition, its risk factors and its warning signs matters, particularly for those with a higher personal or family risk.
Understanding the Stomach and How Stomach Cancer Develops
The stomach is a muscular, J-shaped organ in the upper digestive tract that receives food from the oesophagus, mixes it with digestive acids and enzymes, and gradually releases it into the small intestine for further digestion. The inner surface of the stomach is lined with a layer of specialised cells that produce mucus, acid and digestive enzymes.
Stomach cancer usually begins in this lining. Over time — often years — the lining can undergo a series of changes, sometimes starting with chronic inflammation (gastritis), progressing through pre-cancerous changes in the cells, and eventually developing into cancer in a small proportion of cases. As the cancer grows, it can spread deeper into the layers of the stomach wall, to nearby lymph nodes, and eventually to other organs such as the liver, lungs or the lining of the abdominal cavity (the peritoneum).
What Is Stomach Cancer?
Stomach cancer refers to a group of cancers that begin in different types of cells found in the stomach. There are several recognised types, though the vast majority of cases are adenocarcinoma, which develops from the gland cells lining the stomach.
- Adenocarcinoma: By far the most common type, accounting for the large majority of stomach cancers. It develops from the gland cells that line the inner surface of the stomach and produce mucus.
- Gastrointestinal Stromal Tumor (GIST): A less common type that arises from specialised cells in the stomach wall responsible for controlling digestive muscle movement. GISTs behave differently from adenocarcinoma and often respond well to targeted drug therapy.
- Gastric Lymphoma: A cancer of the immune (lymphatic) tissue found in the stomach wall, often linked to chronic Helicobacter pylori infection. It is generally treated differently from adenocarcinoma, frequently with antibiotics, chemotherapy or radiation.
- Neuroendocrine Tumors (Carcinoid Tumours): Rare tumours arising from hormone-producing cells in the stomach lining. They tend to grow more slowly than adenocarcinoma and can behave in a wide range of ways depending on their specific characteristics.
Stomach cancer has a genetic component and is associated with family history, and is also strongly linked to chronic infection with Helicobacter pylori — a type of bacteria associated with chronic gastritis and recurrent peptic ulcers.
Stages of Stomach Cancer
Once stomach cancer is diagnosed, doctors determine its stage — how far the cancer has grown and spread — as this is one of the most important factors in guiding treatment decisions and understanding prognosis.
- Stage 0: Abnormal cells are found only in the innermost lining of the stomach and have not become invasive cancer (also known as carcinoma in situ).
- Stage I: Cancer has grown into deeper layers of the stomach wall but remains localised, with no or very limited spread to nearby lymph nodes.
- Stage II: Cancer has grown further into or through the stomach wall and may have spread to a moderate number of nearby lymph nodes.
- Stage III: Cancer has spread more extensively into the stomach wall, to nearby organs, or to a larger number of lymph nodes, but has not yet spread to distant parts of the body.
- Stage IV: Cancer has spread to distant organs, such as the liver, lungs or peritoneum (the lining of the abdominal cavity), or distant lymph nodes.
Staging takes into account the depth of tumor invasion into the stomach wall, the number of lymph nodes involved, and whether the cancer has spread to distant organs. Earlier-stage cancers generally offer more treatment options and better outcomes, which underscores the value of timely investigation of persistent digestive symptoms.
Symptoms of Stomach Cancer
Stomach cancer is often asymptomatic in its early stages, which is one of the reasons it can be difficult to detect early. As it develops, a range of symptoms may appear, often overlapping with more common, benign digestive conditions.
Early and Non-Specific Symptoms
- Constant or persistent indigestion
- Unexplained weight loss
- Upper abdominal pain or discomfort
- Loss of appetite
- Heartburn
Symptoms as the Cancer Progresses
- Anaemia, often detected through fatigue or on blood tests
- Black or tarry stools, indicating bleeding within the digestive tract
- Constipation or diarrhoea
- Difficulty swallowing
- Jaundice (yellowing of the skin or eyes), if the cancer affects the liver or bile ducts
- Nausea and vomiting, sometimes with blood
Because these symptoms are common to many digestive conditions, they do not necessarily mean cancer is present — but persistent or worsening symptoms, particularly in someone with known risk factors, warrant proper medical evaluation.
Causes of Stomach Cancer
Stomach cancer develops through an accumulation of genetic changes in stomach lining cells, triggered or accelerated by a combination of inherited and environmental factors.
- Helicobacter pylori infection: A chronic bacterial infection strongly associated with the development of chronic gastritis, peptic ulcers, and, over time, an increased risk of stomach cancer
- Chronic gastritis: Long-term inflammation of the stomach lining can lead to changes in the cells that, in some cases, progress toward cancer over many years
- Genetic and family factors: Family history and inherited genetic changes can meaningfully raise the likelihood of developing stomach cancer, and a small proportion of cases are linked to specific hereditary cancer syndromes
- Diet: A diet consistently high in salted, pickled or smoked foods has been linked to a higher risk, possibly due to certain compounds formed during these preservation processes
Risk Factors for Stomach Cancer
- Age: Stomach cancer is more prevalent in those aged 50 and above
- Chronic gastritis: People who suffer from long-term gastritis may be at a higher risk, as inflammation of the stomach may affect the stomach lining where stomach cancers usually form.
- Diet: A diet high in salt, pickled or smoked food has been linked to a higher risk of stomach cancer.
- Ethnicity: Asians have been linked to a higher risk of stomach cancer.
- Family history: People who have a close family member with a history of stomach cancer face a higher risk of developing stomach cancer themselves.
- Smoking: Smoking increases your risk for developing several types of cancer, including stomach cancer.
- Helicobacter pylori infection: Your risk of stomach cancer increases if you have had a Helicobacter pylori infection.
- Other associated factor: A history of stomach surgery, certain stomach polyps, pernicious anaemia, or a diet low in fruits and vegetables have also been associated with a modestly increased risk in some studies.
How Stomach Cancer Affects the Body
As stomach cancer grows or spreads, it can lead to a range of complications beyond the primary tumour itself.
- Gastrointestinal bleeding: A tumour can bleed slowly into the digestive tract, leading to anaemia, or occasionally cause more significant, sudden bleeding
- Obstruction: A tumour near the entrance or exit of the stomach can partially or fully block the passage of food, causing nausea, vomiting and difficulty eating
- Malnutrition and weight loss: Reduced appetite, difficulty eating, and the metabolic effects of cancer itself can lead to significant, unintentional weight loss and muscle wasting over time
- Ascites: If the cancer spreads to the peritoneum, fluid can accumulate in the abdominal cavity, causing swelling and discomfort
- Metastasis to distant organs: When cancer spreads to the liver, lungs, bones or other distant sites, it can affect the function of those organs and requires broader, systemic treatment
How Is Stomach Cancer Diagnosed?
Diagnosis usually involves a combination of direct visual examination, tissue sampling, and imaging to determine both the diagnosis and the extent of the disease.
- Gastroscopy (Upper Endoscopy): A thin, flexible camera is passed through the mouth to directly examine the oesophagus, stomach and the first part of the small intestine, allowing the doctor to see any abnormal areas directly.
- Biopsy: Small tissue samples are taken during gastroscopy from any suspicious areas and examined under a microscope, providing the definitive diagnosis of stomach cancer and its specific type.
- Blood Tests: A complete blood count can detect anaemia, which may result from chronic bleeding in the stomach, while other blood tests help assess general health and organ function ahead of treatment.
- Imaging Tests (Ultrasound and CT Scan): Used to look for abnormalities in and around the stomach, and to assess whether the cancer has spread to nearby structures, lymph nodes or other organs.
- Endoscopic Ultrasound: Combines endoscopy with ultrasound to assess how deeply a tumour has grown into the layers of the stomach wall and whether nearby lymph nodes are involved, which helps guide treatment planning.
- PET Scan: A whole-body imaging test that can help detect whether cancer has spread beyond the stomach to distant sites, particularly useful in planning treatment for more advanced disease.
- Staging Laparoscopy: A minimally invasive surgical procedure, using small incisions and a camera, to directly inspect the abdominal cavity for small deposits of cancer that may not show up clearly on scans, most often used before major surgery.
Living Well After Stomach Cancer
Because the stomach plays such a central role in digestion, surgery for stomach cancer — particularly a total or subtotal gastrectomy — often requires significant, lasting adjustments to how a person eats.
- Smaller, more frequent meals: Without a full-sized stomach to hold food, most patients need to eat smaller, more frequent meals rather than three large ones
- Dumping syndrome: Rapid movement of food into the small intestine after gastrectomy can cause dumping syndrome, with symptoms such as cramping, nausea, sweating and light-headedness after eating, particularly with sugary or high-carbohydrate foods
- Vitamin and mineral supplementation: The stomach normally helps absorb vitamin B12 and iron; after gastrectomy, patients often require lifelong vitamin B12 injections or supplementation, along with monitoring for iron and other nutrient deficiencies
- Working with a dietitian: A dietitian can help design an eating plan that supports adequate nutrition and weight while minimising digestive discomfort during the adjustment period after surgery
With time, guidance and support, most patients adapt well to these changes and are able to maintain good nutrition and a satisfying relationship with food.
Preventing Stomach Cancer
While not all cases of stomach cancer can be prevented, several strategies can meaningfully reduce risk or support earlier detection.
- Helicobacter pylori infection: A chronic bacterial infection strongly associated with the development of chronic gastritis, peptic ulcers, and, over time, an increased risk of stomach cancer
- Chronic gastritis: Long-term inflammation of the stomach lining can lead to changes in the cells that, in some cases, progress toward cancer over many years
- Genetic and family factors: Family history and inherited genetic changes can meaningfully raise the likelihood of developing stomach cancer, and a small proportion of cases are linked to specific hereditary cancer syndromes
- Diet: A diet consistently high in salted, pickled or smoked foods has been linked to a higher risk, possibly due to certain compounds formed during these preservation processes
