Stomach Cancer Diagnosis and Staging

April 28, 2025

This page was reviewed under our medical and editorial policy by Yanghee Woo, M.D., associate professor, Division of Surgical Oncology, Department of Surgery, City of Hope^® Orange County Lennar Foundation Cancer Center.

In the United States, where there are no national screening guidelines, stomach cancer is typically found after a person has symptoms that spur a visit to the doctor. In general, the evaluation begins with a medical history (where the doctor asks about symptoms and potential risk factors for stomach cancer), as well as a physical exam (where the doctor will, for example, feel the abdomen for any signs of abnormalities). Patients typically see a gastroenterologist, an expert in assessing and treating digestive system problems, to guide this process.

If stomach cancer is suspected, a series of tests are needed to make an accurate diagnosis.

If cancer is found, the health care team may order additional testing to understand the extent of the disease.

Stomach Cancer Tests

A variety of tests may be used to make a diagnosis and determine the extent of the cancer (staging). These tests include the following.

Upper Endoscopy

This procedure is the primary test and considered the gold standard for diagnosing stomach cancer. After the patient is sedated, the doctor threads an endoscope — a thin, flexible tube outfitted with a tiny video camera — down the patient’s throat and into the stomach. If the doctor sees any abnormalities in the stomach lining, small pieces of tissue may be removed (biopsied) at that time for examination under a microscope.

Testing Biopsy Samples

Upper endoscopy is able to spot suspicious-looking tissue, but the only way to determine whether it's cancer is by examining biopsy samples. If it is stomach cancer, the tissue may also be evaluated using the following tests to glean other important information, including whether it carries gene mutations that may affect a patient’s stomach cancer treatment options.

HER2 testing: This shows whether the cancer cells have high amounts of a protein called HER2, which promotes cell growth. Cancers that are deemed HER2-positive may be treated with drugs that target this protein.

PD-L1 testing: Some cancer cells have large amounts of a protein called PD-L1, which impedes the immune system’s ability to destroy them. If a stomach cancer has high PD-L1 levels, treatment with drugs called immune checkpoint inhibitors may be an option.

Tests for microsatellite instability and mismatch repair deficiency: These are genetic defects found in certain cancers, including some cases of stomach cancer. If they are present, an immune checkpoint inhibitor may be an option.

Tumor mutational burden: This testing shows whether stomach cancer cells have a large number of genetic mutations. If so, an immune checkpoint inhibitor may be an option.

NTRK testing: Some cancers have particular changes in genes known as NTRK. If they are found, certain targeted drugs may be a treatment option.

Imaging Tests

Various types of imaging may also be used to help diagnose stomach cancer or to give additional information about it, such as the extent to which it might have spread. Sometimes, imaging studies obtained for other reasons may detect a tumor or mass in the stomach and associated enlarged lymph nodes.

Imaging tests may also be used to determine the stage of stomach cancer after the disease has been diagnosed. Accurate staging provides essential information for optimizing stomach cancer treatment.

Endoscopic ultrasound: This imaging test is often used to gauge the extent to which a tumor has burrowed into the stomach wall, or spread beyond the stomach. The procedure is similar to an upper endoscopy, but uses a scope with a small ultrasound probe at its tip. The probe is placed against the stomach wall, in the area of the cancer, where it gives off sound waves and detects echoes as they bounce back. The echoes are converted into images of the stomach wall layers, as well as the structures just outside the stomach.

Computed tomography (CT) scan: This type of imaging takes detailed pictures of the body’s tissues from various angles. It may help confirm the location of a stomach tumor and whether it has spread to nearby lymph nodes or other organs. CT scans of the chest, abdomen and pelvis are very important during stomach cancer staging.

Positron emission tomography (PET) scan: For this type of imaging, the patient receives an injection of a special sugar that is slightly radioactive. It collects within cancer cells, causing them to “light up” on imaging. A PET scan may help determine the extent of a stomach cancer. Alternatively, doctors may use a combined PET/CT scan (done at the same time, in the same scanner) for this purpose. While PET scans may be useful for most stomach cancers, a small percentage of stomach cancers don’t light up on PET scans.

Magnetic resonance imaging (MRI): Like CT, this type of imaging provides detailed pictures of body tissue, but it uses a magnet and radio waves instead of X-rays. It's used less often than CT in evaluating stomach cancer, but it may be helpful at certain times if the doctor wants to assess whether the cancer has spread to the liver, for example.

Upper gastrointestinal (GI) series: This is an X-ray test in which the patient first drinks a liquid containing barium, a silver-white metallic compound that coats the lining of the throat, stomach and small intestine. This helps to highlight any areas of abnormal tissue. This test is not often performed, as upper endoscopy is generally a preferred approach. However, it's less invasive and may be useful in some cases.

Diagnostic or Staging Laparoscopy

This is a minimally invasive surgery in which a doctor inserts a scope through small incisions in the abdomen. Peritoneal washings to detect cancer cells and biopsies of peritoneal lesions may be taken during the staging laparoscopy. It is recommended that all patients with more than an early stage stomach cancer receive a laparoscopy after a stomach cancer diagnosis to confirm that the disease hasn’t spread outside of the stomach. It may allow doctors to detect occult cancer in the lining of the abdominal cavity and internal organs by direct visualization, and microscopic cancer cells by using biopsies and washings. CT scans and PET/CT scans may not visualize smaller lesions and cells.

Stomach Cancer Stages

Stomach cancer diagnosis also involves staging, which describes the extent of the cancer, including the tumor size, whether it has spread to the draining lymph nodes and other organs beyond its original site and, if so, how far it has spread. Staging is key to devising a correct treatment plan, and it also gives a general idea of a patient’s prognosis.

Stomach cancer is usually staged according to the TNM system:

• T refers to characteristics of the main tumor
• N describes whether it has spread to lymph nodes near the stomach
• M describes whether it has spread to distant sites in the body, or metastasized

Stage 0 Stomach Cancer

This earliest stage is a precancerous condition also known as carcinoma in situ. Abnormal cells are present only in the innermost layer of the stomach lining (the mucosa) and have not turned into invasive tumors.

Stage 1 Stomach Cancer

Stage 1 stomach cancer is broken down into Stage 1a and Stage 1b.

Stage 1a: Cancer is present in the mucosa and may have spread to the submucosa (the second layer of connective tissue between the mucosa and muscle).

Stage 1b: The cancer may have reached the submucosa and spread to one or two nearby lymph nodes, or it has grown deeper into the stomach wall, reaching the thick muscular layer, but it has not spread to any lymph nodes.

Stage 2 Stomach Cancer

Stage 2 stomach cancer is broken down into Stage 2a and Stage 2b.

Stage 2a: The cancer may have reached the submucosa and spread to three to six nearby lymph nodes, or it is growing into the muscle and has spread to one or two lymph nodes. This stage also includes cancer that has grown past the muscle layer into the subserosa (a layer of connective tissue just under the outer layer of the stomach).

Stage 2b: The cancer has grown no farther into the stomach wall than the submucosa and has spread to seven to 15 nearby lymph nodes, or it has grown into the muscle layer and has spread to three to six nearby lymph nodes. Cancer is also Stage 2b if it has grown into the subserosa and has spread to one or two nearby lymph nodes or if it has reached the stomach’s outer covering (called the serosa), but it has not spread beyond the stomach.

Stage 3 Stomach Cancer

Stage 3 stomach cancer is broken down into Stage 3a, Stage 3b and Stage 3c.

Stage 3a: Cancer has reached the muscle layer and spread to seven to 15 nearby lymph nodes; or it has spread to the subserosa and three to six lymph nodes; or it has reached the serosa and one to six lymph nodes. Cancer that has spread to nearby organs or tissues, such as the spleen, colon, liver or diaphragm, but not to any lymph nodes or distant sites in the body, is also stage 3a.

Stage 3b: The cancer has grown into the submucosa or muscle layer, and spread to 16 or more nearby lymph nodes; or it has grown into the subserosa layer or the serosa, and has spread to seven to 15 lymph nodes. Cancer that has spread to nearby organs or tissues, as well as up to six nearby lymph nodes, is also Stage 3b.

Stage 3c: The cancer has grown into the subserosa or serosa, and has spread to 16 or more nearby lymph nodes; or it has moved into nearby organs or tissues, as well as seven or more nearby lymph nodes.

Stage 4 Stomach Cancer

Stage 4 stomach cancer has spread to more distant parts of the body, such as the lungs, brain or the membrane that lines the abdomen and pelvis.