Stomach cancer, also known as gastric cancer, is a type of gastrointestinal cancer that, like many other cancers, is the most treatable when it is caught in its earliest stages. 

Since routine screening is not available for stomach cancer, it is typically detected after a person visits their doctor for symptoms associated with the disease. For people with conditions that increase their risk of developing stomach cancer, the same tests used to detect stomach cancer are also used to evaluate high-risk individuals.

Tests Used for Diagnosing Stomach Cancer

If stomach cancer is suspected, you may be referred to a gastroenterologist — a doctor who specializes in digestive diseases — for further testing to confirm a diagnosis. These diagnostic tests help the doctor recommend the most effective treatment for you. 

Often, the first exam a GI doctor will perform is a physical one to check your abdomen for any abnormalities while further discussing your symptoms and medical history. To determine the presence of stomach cancer, they will recommend one or more of the following tests:

Upper Endoscopy

This procedure involves the use of an endoscope, a thin, lighted tube, to examine the esophagus, stomach, and duodenum (the first part of the small intestine). They will be looking specifically for precancerous cells and tumors.

Biopsy

If something is spotted in the endoscopy they can usually take a small tissue sample during that procedure. Some patients have a separate biopsy, especially if cancer is suspected in the lower stomach. This can be harder to see during an endoscopy so a different technique is used. An endoscopic ultrasound allows the doctor to guide the needle to the area of concern so that a tissue sample can be removed. A biopsy is the only way to confirm if cancer is present. A pathologist will review the samples under a microscope to provide more detailed information about the type of cells found. 

Imaging Tests

Imaging tests use X-rays, magnetic fields, sound waves, or radioactive substances to create images of the inside of your body. Some imaging may be done before cancer is diagnosed to get a better look at areas of concern. Other imaging tests are done once a tumor is found to be cancerous to determine whether surgery is possible and if the cancer has spread.  

Several types of imaging tests may be used to identify the location of tumors and any cancer spread outside of the stomach.

  • Barium Swallow (Upper GI Series): This test involves a series of X-rays of the esophagus, stomach and part of the small intestine. The patient drinks a liquid containing barium (a silver-white metallic compound), which coats the esophagus and stomach before the X-rays are taken.
  • CT (CAT) Scan: A CT scan uses a computer connected to an X-ray machine to produce detailed images of areas inside the body from various angles. A dye may be injected into a vein or given orally to enhance the visibility of the organs or tissues. 
  • Positron Emission Tomography (PET) Scan: During a PET scan, a slightly radioactive form of sugar is injected into the body. This sugar is primarily absorbed by cancer cells, which are attracted to sugar more quickly than healthy cells. The PET scanner then captures images of the areas that show radioactivity. When a CT scan is performed at the same time, it is referred to as a PET/CT scan.
  • Magnetic resonance imaging (MRI): An MRI uses a magnet, radio waves, and a computer to create a series of detailed images of areas inside the body. This is used less often than a CT scan for stomach cancer.

Biomarker Testing Stomach Cancer Cells

When gastric cancer is found, additional testing of the biopsy sample is done to determine if the cells have specific gene or protein changes that could influence treatment. This is called biomarker testing.

For stomach cancer, biomarker testing looks for these types of gene or protein changes:

  • HER2: The cancer cells may have higher than normal amounts of a protein called HER2.
  • PD-L1: The cells may have elevated levels of an immune checkpoint protein known as PD-L1.
  • NTRK: The cells may have changes in one of the NTRK genes. 
  • Mismatch repair deficiency: The cells may have a defect in a mismatch repair gene. 
  • Tumor mutational burden: A high tumor mutational burden indicates that the cells have numerous gene mutations.  
  • Microsatellite instability: The cells may show microsatellite instability, which can result from mistakes that aren't corrected during DNA replication. 

What’s Next After a Gastric Cancer Diagnosis?

If any of these tests confirm the presence of stomach cancer, the next step will be to determine the extent of the cancer through a process called staging. Blood tests and heart scans may also be conducted to ensure proper organ function before surgery to remove the cancer is planned. 

Learn more about the stages of stomach (gastric) cancer. 

Once stomach cancer staging is complete, your oncologist considers factors such as your type of stomach cancer, its extent and the genetic profile of the tumor as a guide for creating a personalized stomach cancer treatment plan.