Different Types of Stomach Cancer

Stomach (gastric) cancer is not a single disease.

Different types of tumors can develop in the stomach, and even cancers that look similar under the microscope may behave differently. The type of tumor, its location and stage, histological features, and molecular characteristics can all influence treatment and prognosis.

When people refer to stomach cancer, they are usually referring to gastric adenocarcinoma, which accounts for the great majority of cancers that begin in the stomach.

Other tumors can also arise in the stomach, including:

• Gastrointestinal stromal tumors (GISTs)
• Neuroendocrine tumors (NETs)
• Primary gastric lymphomas
• Rare tumors such as squamous cell carcinoma and other unusual malignancies

These tumors are biologically different from gastric adenocarcinoma and may require very different treatments. Establishing the exact pathological diagnosis is therefore an essential first step in treatment planning.

 

Gastric Adenocarcinoma Is Also Not a Single Disease

Even within gastric adenocarcinoma, there is considerable variation.

Pathologists evaluate how the cancer cells grow, how closely they resemble normal stomach tissue, and whether particular microscopic features are present.

Common histological patterns include:

• Tubular adenocarcinoma
• Papillary adenocarcinoma
• Mucinous adenocarcinoma
• Poorly cohesive carcinoma, including tumors with signet-ring cells

Another widely used system, the Lauren classification, divides gastric adenocarcinomas mainly into intestinal and diffuse types, with some tumors showing mixed or indeterminate features.

These classifications provide useful information about tumor biology and patterns of spread, but they are only one part of the overall assessment.

 

Tumor Location Matters

Stomach cancer can arise in different parts of the stomach, from the cardia, where the stomach meets the esophagus, to the body and distal stomach or antrum.

Tumor location can influence:

• The type and extent of surgery
• Which lymph nodes need to be removed
• How tumors near the gastroesophageal junction are classified and treated
• How the digestive tract is reconstructed after surgery
• The overall treatment strategy

For example, a cancer in the distal stomach may require a very different operation from one involving the upper stomach or gastroesophageal junction.

Location alone, however, does not determine how a cancer will behave. Stage, histology, molecular characteristics, and response to treatment are also important.

 

Some Gastric Cancers Grow in Different Ways

Gastric cancers can differ in how they grow within the stomach.

Some form a localized mass or ulcer, while others spread more diffusely through the stomach wall.

One important example is linitis plastica, in which diffuse tumor infiltration causes the stomach wall to become thickened and rigid. This pattern is often associated with diffuse or poorly cohesive gastric cancer and can be more difficult to assess because tumor cells may extend beyond what is immediately visible during endoscopy.

The growth pattern can therefore influence staging, surgical planning, and the ability to achieve complete tumor removal.

 

Tumor Grade Provides Additional Information

Pathologists also assess how differentiated the cancer cells appear compared with normal stomach tissue.

Tumors may be described as well differentiated, moderately differentiated, or poorly differentiated. Poorly differentiated tumors look less like normal stomach tissue and may be associated with more aggressive biological behavior.

However, grade should not be interpreted in isolation. Stage and other pathological and molecular characteristics are also important in determining prognosis and treatment.

 

Stage Is One of the Most Important Differences

The stage describes how far the cancer has spread and is one of the most important factors in determining treatment and prognosis.

The internationally used TNM system considers:

• T (Tumor): How deeply the cancer has grown into or through the stomach wall
• N (Nodes): Whether regional lymph nodes contain cancer
• M (Metastasis): Whether the cancer has spread to distant sites

Very early cancers may sometimes be treated with endoscopic resection alone.

Localized cancers that extend more deeply into the stomach usually require surgery and, depending on the stage and individual circumstances, systemic treatment before and/or after surgery.

When cancer has spread to distant organs or the peritoneum, systemic therapy generally becomes the main treatment. Selected patients may also benefit from carefully chosen surgical or other local treatments as part of an individualized multidisciplinary strategy.

 

Molecular Characteristics Can Change Treatment

Modern gastric cancer treatment considers not only what the tumor looks like under the microscope, but also its molecular and immune characteristics.

Depending on the stage and clinical situation, testing may include:

• HER2
• Mismatch repair (MMR) or microsatellite instability (MSI)
• PD-L1
• Claudin 18.2 (CLDN18.2)

These biomarkers can influence the use of targeted therapy and immunotherapy, particularly in advanced disease.

For example, HER2-positive cancers may benefit from HER2-directed therapy, while MSI-high (MSI-H) or mismatch repair-deficient (dMMR) cancers may be particularly sensitive to immune checkpoint inhibitors. CLDN18.2 can also identify selected patients with advanced gastric cancer who may benefit from CLDN18.2-directed treatment.

As a result, two patients with gastric adenocarcinoma at a similar stage may receive different treatments because the biological characteristics of their tumors are different.

 

Why These Differences Matter

The term “stomach cancer” therefore describes a group of biologically different cancers rather than one uniform disease.

For an individual patient, treatment planning may depend on:

• The exact tumor type
• Histological subtype
• Tumor location
• Stage and lymph-node involvement
• Pattern of spread
• Molecular and immune biomarkers
• Whether complete surgical removal is possible
• Overall health and nutritional condition

This is why treatment should not be based simply on the diagnosis of “gastric cancer.”

The right treatment depends on understanding what type of stomach cancer is present, how far it has spread, how it is likely to behave, and which treatments are most likely to benefit the individual patient.