Stomach cancer

What it is

Stomach cancer, also called gastric cancer, is a cancer that starts in the stomach lining and is usually an adenocarcinoma. The most important practical fact is that early gastric cancer is limited to the mucosa or submucosa, regardless of lymph node status, and cancers found at this stage are more likely to be treated successfully than cancers found after deeper spread. Most stomach cancers arise from the gland-forming cells of the stomach lining, but the exact location can vary, including the main body of the stomach or the gastroesophageal junction where the food pipe meets the stomach.

Stomach cancer usually develops over years rather than days or weeks. In many people, it is preceded by long-standing inflammation of the stomach lining, often related to Helicobacter pylori infection, autoimmune gastritis, or a sequence of precancerous changes such as atrophic gastritis and intestinal metaplasia. Not every person with these conditions develops cancer.

A simple way to think about stomach cancer is:

Feature	Key point
Most common type	Adenocarcinoma
Common starting point	Inner lining of the stomach
Early stage definition	Limited to mucosa or submucosa
Major risk factor	H. pylori infection
Main diagnostic test	Upper GI endoscopy with biopsy

In India, stomach cancer is less common than some other cancers nationally, but rates are higher in certain regions and populations. As in other countries, delayed diagnosis can happen because early symptoms often look like common indigestion or acidity.

How it works

Stomach cancer begins when cells in the stomach lining acquire DNA changes that let them grow, survive, and invade when they should not. Over time, these abnormal cells can form a tumour, grow through the stomach wall, spread to nearby lymph nodes, and later travel to organs such as the liver or the lining of the abdomen.

Several biological pathways can lead to gastric cancer:

1. Chronic inflammation pathway: Long-term inflammation, especially from H. pylori, can lead to atrophic gastritis, intestinal metaplasia, dysplasia, and then cancer.
2. Diffuse-type pathway: Some cancers, including hereditary forms, arise without the classic precancerous sequence and may infiltrate the stomach wall more diffusely.
3. Reflux-related junction cancers: Tumours near the gastroesophageal junction may be linked more closely to reflux and obesity patterns seen in some populations.

Pathologists and clinicians often classify gastric adenocarcinoma into two broad histologic patterns:

Type	General features
Intestinal type	More often linked to chronic gastritis, intestinal metaplasia, and environmental risk factors
Diffuse type	More infiltrative, may occur in younger people, and can be associated with hereditary syndromes

This classification helps explain why stomach cancer does not behave the same way in every patient.

Evidence and uses

The main use of the term in clinical care is to describe a specific cancer diagnosis that then guides staging and treatment. Symptoms can include indigestion, upper abdominal pain, bloating after meals, early fullness, nausea, vomiting, trouble swallowing, black stools, anaemia, and unintentional weight loss. These symptoms are not specific to cancer, which is one reason diagnosis may be delayed.

Risk factors supported by clinical evidence include:

• H. pylori infection
• Smoking
• Diets high in salted, smoked, or preserved foods
• Low intake of fruits and vegetables
• Older age
• Male sex
• Family history of gastric cancer
• Certain hereditary cancer syndromes
• Chronic atrophic gastritis, intestinal metaplasia, or gastric dysplasia
• Prior stomach surgery in some settings

There is good evidence that preventing or treating H. pylori can reduce the risk of non-cardia gastric cancer in some populations, especially before advanced precancerous changes develop. However, risk reduction is not the same as complete prevention.

Treatment depends on stage, tumour location, pathology, and the person's overall health. Common treatment approaches include:

Stage or situation	Common treatment approach
Very early, selected lesions	Endoscopic resection in carefully chosen cases
Localised disease	Surgery, often combined with chemotherapy before and/or after surgery
Some locally advanced cases	Chemoradiation may be used in selected settings
Metastatic disease	Systemic therapy such as chemotherapy, targeted therapy, immunotherapy, and symptom control

Biomarker testing is increasingly important in advanced disease. Depending on the case, doctors may test for HER2, mismatch repair or microsatellite instability, PD-L1 expression, and sometimes other molecular markers. These results can affect whether targeted therapy or immunotherapy is an option.

Evidence for screening the general population is not uniform worldwide. Countries with high incidence such as Japan and Korea have organised screening strategies, but many countries, including India, do not have population-wide gastric cancer screening programmes. In practice, Indian patients are more often diagnosed after symptoms prompt endoscopy.

Diagnosis / how it's measured

Stomach cancer cannot be diagnosed reliably from symptoms alone. The standard first test when cancer is suspected is upper gastrointestinal endoscopy with biopsy. During endoscopy, a doctor passes a flexible camera through the mouth into the stomach and takes tissue samples from suspicious areas.

After biopsy confirms cancer, staging usually involves a combination of tests:

1. CT scan of the chest, abdomen, and pelvis to look for spread.
2. Endoscopic ultrasound in selected cases to assess depth of invasion and nearby lymph nodes.
3. PET scan in some patients, especially when it may change management.
4. Diagnostic laparoscopy for potentially operable cancers, because small peritoneal deposits may not show on scans.
5. Blood tests to assess anaemia, liver function, nutrition, and fitness for treatment.

Doctors stage stomach cancer using the TNM system:

• T: how deeply the tumour has grown into the stomach wall
• N: whether nearby lymph nodes contain cancer
• M: whether the cancer has spread to distant sites

Pathology reports may also describe grade, Lauren type, margin status after surgery, lymphovascular invasion, and biomarker results.

When to see a clinician

See a clinician promptly if you have persistent indigestion, early fullness, unexplained vomiting, black stools, trouble swallowing, anaemia, or unintentional weight loss, especially if symptoms last more than a few weeks. Urgent assessment is important if there is vomiting blood, severe weakness, dehydration, or signs of bowel obstruction.

People with a strong family history of gastric cancer, known hereditary cancer syndromes, prior gastric dysplasia, or documented intestinal metaplasia may need specialist follow-up even if they feel well. If H. pylori infection is found, treatment and confirmation of eradication are important parts of risk reduction.

Limitations and open questions

Not all stomach cancers follow the same pathway, and symptoms in early disease are often vague. That makes early detection difficult outside formal screening programmes. Even with modern imaging, small peritoneal metastases can be missed until laparoscopy or surgery.

Research is ongoing on who benefits most from surveillance for precancerous stomach lesions, how best to use molecular classification in routine care, and which biomarkers most accurately predict benefit from immunotherapy or targeted drugs. Evidence is stronger for some subgroups than others. Survival and treatment response vary widely by stage at diagnosis, tumour biology, access to specialist care, and nutritional status.

Because treatment decisions can involve surgery, chemotherapy, radiation, targeted therapy, and supportive care, stomach cancer is best managed by a multidisciplinary team that includes gastroenterology, surgical oncology, medical oncology, pathology, radiology, and nutrition support.