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Tests for Stomach Cancer

Stomach cancer (also known as gastric cancer) is usually found when a person goes to the doctor because of signs or symptoms they are having. If stomach cancer is suspected, exams and tests will be needed to find out for sure.

If cancer is found, other tests will be done to learn more about it.

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Medical history, physical exam, and tests to look for bleeding
Upper endoscopy
Biopsy
Imaging tests
Other tests
Questions to ask if you’re told you have stomach cancer

Medical history, physical exam, and tests to look for bleeding

When taking your medical history, the doctor will ask about your symptoms (such as eating problems, pain, bloating, etc.) and possible risk factors to see if they might suggest stomach cancer or another cause.

The physical exam can give your doctor information about possible signs of stomach cancer or other health problems. In particular, the doctor will feel your belly for anything abnormal.

The doctor might order a blood test to look for anemia (a low red blood cell count), which could be caused by the cancer bleeding into the stomach. A test might also be done to look for blood in your stool (feces), which could also be a sign of bleeding in the stomach.

If your doctor thinks you might have stomach cancer or another type of stomach problem, they will likely refer you to a gastroenterologist (a doctor who treats diseases of the digestive tract), who will examine you and might do further testing.

Upper endoscopy

Upper endoscopy (also called esophagogastroduodenoscopy or EGD) is the test most often done if the doctor thinks you might have stomach cancer.

During this test, the doctor passes an endoscope, which is a thin, flexible, lighted tube with a small video camera on the end, down your throat. This lets the doctor see the inner lining of your esophagus, stomach, and first part of the small intestine. If abnormal areas are seen, biopsy samples can be removed using instruments passed through the endoscope. The tissue samples are sent to a lab, where they are looked at with a microscope to see if they contain cancer.

Unfortunately, some types of stomach cancers can be hard to see during an endoscopy.

Endoscopy can also be used as part of a special imaging test known as endoscopic ultrasound, which is described below.

In some situations, endoscopy can be used to remove very early-stage cancers. Sometimes it might also be used to help prevent or relieve symptoms or other complications from stomach cancer, instead of more extensive surgery. (See Surgery for Stomach Cancer.)

You will most likely be given medicine to make you sleepy (sedation) before the endoscopy.

Biopsy

Your doctor may suspect cancer if an abnormal-looking area is seen on endoscopy or an imaging test, but the only way to be sure is by doing a biopsy. During a biopsy, the doctor removes small pieces (samples) of the abnormal area.

Biopsies to check for stomach cancer are most often done during an upper endoscopy. If the doctor sees any abnormal areas in the stomach lining during the endoscopy, instruments can be passed through the endoscope to biopsy them.

Some stomach cancers start deep within the stomach wall, which can make them hard to biopsy with standard endoscopy. If the doctor suspects cancer might be deeper in the stomach wall, endoscopic ultrasound (described below) can be used to guide a thin, hollow needle into the wall of the stomach to get a biopsy sample.

Samples may also be taken from areas of possible cancer spread, such as nearby lymph nodes or suspicious areas in other parts of the body.

Testing biopsy samples

The biopsy samples are sent to a lab to be looked at with a microscope. The samples are checked to see if they contain cancer, and if they do, what kind it is.

If cancer cells are found, more lab tests will likely be done on the biopsy samples to learn more about them. This might affect how the cancer is treated.

The cancer cells will likely be tested to see if they have too much of a protein called HER2 that helps the cells grow. Cancers with increased levels of HER2 are called HER2-positive. These cancers can be treated with drugs that target the HER2 protein.

The biopsy sample is usually tested for HER2 using either immunohistochemistry (IHC) or fluorescent in situ hybridization (FISH). Often the IHC test is used first, which gives results on a scale from 0 to 3+.

If the results are 0 or 1+, the cancer is HER2-negative, so drugs targeting HER2 aren’t likely to be helpful.
If the result comes back 3+, the cancer is HER2-positive, so treatment with drugs targeting HER2 could be an option.
When the result is 2+, the HER2 status of the cancer is not clear, so it needs to be tested with FISH to clarify the result.

The cancer cells will most likely be tested for other gene or protein changes that might affect treatment. For example:

If the cells have a certain amount of an immune checkpoint protein called PD-L1, treatment with an immune checkpoint inhibitor might be an option.
If the cells have high levels of microsatellite instability (MSI-H), a defect in a mismatch repair gene (dMMR), or a high tumor mutational burden (TMB-H), treatment with an immune checkpoint inhibitor might be an option, even before surgery.
If the cells have high levels of the CLDN18.2 protein, treatment with a drug that targets this protein might be helpful.
If the cells have changes in one of the NTRK genes, the BRAF gene, or the RET gene, certain targeted therapy drugs might be an option for treatment.

See How Biopsy and Cytology Samples Are Tested for Cancer to learn more about different types of biopsies and tests, how they are used to diagnose cancer, and what the results can tell you.

Imaging tests

Imaging tests use x-rays, magnetic fields, sound waves, or radioactive substances to create pictures of the inside of your body. They may be done for a number of reasons, including:

To help find out if a suspicious area might be cancer
To learn how far cancer may have spread
To help determine if treatment is working
To look for possible signs of cancer coming back

This test, also called a barium swallow, is an x-ray test to look at the inner lining of the esophagus, stomach, and first part of the small intestine. This test is used much less often than it was in the past, as it can miss some abnormal areas, and unlike upper endoscopy it doesn't allow the doctor to take biopsy samples. But it is less invasive than endoscopy, and it might be useful in some situations.

For this test, you drink a chalky solution containing a substance called barium. The barium coats the inner lining of the esophagus, stomach, and small intestine. (Air might be pumped into your stomach through a thin tube at this time as well.) Several x-rays are then taken. Because x-rays can’t pass through the coating of barium, they outline any abnormal areas in the lining of these organs.

A CT scan uses x-rays to make detailed, cross-sectional images of the soft tissues in the body.

CT scans can show the stomach fairly clearly and often can confirm the location of a cancer. CT scans can also show other parts of the body that stomach cancer might have spread to, such as the liver and nearby lymph nodes. This can help determine the extent (stage) of the cancer and if surgery may be a good treatment option.

CT-guided needle biopsy: CT scans can also be used to guide a biopsy needle into a suspected area of cancer spread. For this test, you lie on the CT scanning table while the doctor moves a biopsy needle through the skin toward the mass. CT scans are repeated until the needle is within the mass. A biopsy sample is then removed and sent to a lab for testing.

Endoscopic ultrasound (EUS) is often used to see how far cancer might have spread into the wall of the stomach, or into nearby areas or nearby lymph nodes.

This test is typically done as part of an upper endoscopy (see above). A small ultrasound probe is placed on the tip of the endoscope. While you are sedated, the endoscope is passed down your throat and into the stomach. The probe is put up against the wall of the stomach where the cancer is. It gives off sound waves and detects the echoes as they bounce back, which are then converted into images. Doctors can use these images to look at the layers of the stomach wall, as well as the nearby lymph nodes and other structures just outside the stomach.

EUS can also be used to help guide a needle into a suspicious area to get a biopsy sample (known as an EUS-guided needle biopsy).

A PET scan can help determine the extent of the cancer in the body. For this test, you are injected with a slightly radioactive form of sugar, which will collect mainly in cancer cells. A special camera is then used to create a picture of areas of radioactivity in the body. The picture is not as detailed as a CT scan, but a PET scan can look for possible areas of cancer spread all over the body at once.

Many newer machines can do both a PET and CT scan at the same time (PET/CT scan). This lets the doctor see areas that “light up” on the PET scan in more detail.

Although PET scans can be useful for finding areas of cancer spread, they aren’t always helpful in certain kinds of stomach cancer because some types don’t take up much of the radioactive sugar.

Like a CT scan, an MRI can show detailed images of soft tissues in the body. But MRIs use radio waves and strong magnets instead of x-rays.

This test is not used as often as CT scans to look for stomach cancer, but it may be helpful in certain situations, such as when looking for tumors in the liver.

Other tests

Laparoscopy

If stomach cancer has already been found, and imaging tests such as CT or PET scans have not shown it has spread to other parts of the body, doctors might do a staging laparoscopy before any other surgery. This can help confirm the cancer is still only in the stomach, which means surgery to remove it might still be an option.

This procedure is done in an operating room while you are under general anesthesia (in a deep sleep). A laparoscope (a thin, flexible tube with a small video camera on the end) is inserted through a small cut in the skin over the belly. This lets the doctor look closely at the surfaces of the organs and nearby lymph nodes inside the abdomen, or even biopsy (remove) small samples of tissue, which can then be tested for cancer.

If it doesn’t look like the cancer has spread, sometimes the doctor will “wash” the abdomen with saline (saltwater) and then collect it to check for cancer cells. This is called peritoneal washing.

Sometimes laparoscopy is combined with ultrasound to give a better picture.

Tests of organ function

If cancer is found, the doctor might recommend certain lab tests, especially if surgery might be an option. For instance, blood tests will be done to make sure your liver and kidneys are working normally, that your blood counts are normal, and that your blood clots like it should.

If surgery is planned or you are going to get medicines that can affect your heart, you may also get an electrocardiogram (EKG) and/or an echocardiogram (an ultrasound of the heart) to make sure your heart is functioning well.

Questions to ask if you’re told you have stomach cancer

What type of stomach cancer do I have?
Where in my stomach is the cancer?
What is the stage of my cancer, and what does that mean in my case?
Will I need any other tests before we can decide on treatment?
Will I need to see any other types of doctors or health professionals?
How much experience do you have treating this type of cancer?
Based on what you’ve learned about my cancer, what is my prognosis (outlook)?
If I’m concerned about the costs and insurance coverage for my diagnosis and treatment, who can help me?

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References

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Developed by the American Cancer Society medical and editorial content team with medical review and contribution by the American Society of Clinical Oncology (ASCO).

Ku GY, Ilson DH. Chapter 72: Cancer of the Stomach. In: Niederhuber JE, Armitage JO, Doroshow JH, Kastan MB, Tepper JE, eds. Abeloff’s Clinical Oncology. 6th ed. Philadelphia, Pa: Elsevier; 2020.

Mansfield PF. Clinical presentation, diagnosis, and staging of gastric cancer. UpToDate. 2020. Accessed at https://www.uptodate.com/contents/clinical-presentation-diagnosis-and-staging-of-gastric-cancer on December 8, 2025.

National Cancer Institute. Stomach Cancer Diagnosis. 2023. Accessed at https://www.cancer.gov/types/stomach/diagnosis on December 8, 2025.

National Comprehensive Cancer Network. NCCN Clinical Practice Guidelines in Oncology: Gastric Cancer. v.3.2025. Accessed at www.nccn.org on December 8, 2025.

Last Revised: February 27, 2026

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