How is Stomach Cancer Diagnosed?

If your doctor suspects you may have stomach cancer based on your symptoms or test results, there are several procedures and tests that can confirm the diagnosis. Some tests are used to determine whether cancer is present. Others are used to learn more about the cancer, including how far it has spread, which is important for planning treatment. You may not need all of the tests listed here.

Medical history and physical examination

Your doctor will begin with a thorough medical history and physical examination. They will ask about your symptoms, how long you have had them, your diet, your history of stomach problems such as ulcers or H. pylori infection, any family history of stomach cancer, and other risk factors including smoking and alcohol use. During the physical exam, your doctor will feel your abdomen for any masses or tenderness, check for swollen lymph nodes, and look for signs such as jaundice or abdominal fluid that might suggest the cancer has spread.

Upper endoscopy

Upper endoscopy, also called esophagogastroduodenoscopy or EGD, is the most important test for diagnosing stomach cancer. A thin, flexible tube with a light and camera on the end is passed through the mouth, down the esophagus, and into the stomach and first part of the small intestine. The doctor can see the inside of the stomach directly and look for abnormal areas such as ulcers, masses, or areas of unusual color or texture. During endoscopy, biopsies can be taken from any suspicious area. Endoscopy is the only way to reliably detect early stomach cancer.

Biopsy

A biopsy is the only way to confirm a diagnosis of stomach cancer. During endoscopy, one or more small tissue samples are taken from the suspicious area using instruments passed through the endoscope. The tissue samples are sent to a pathology laboratory, where a pathologist examines them under a microscope to determine whether cancer cells are present and, if so, what type of cancer it is.

Blood tests

Blood tests do not diagnose stomach cancer directly, but they provide important information about your overall health and help plan treatment:

• Complete blood count. Checks for anemia, which is common in people with stomach cancer due to blood loss from the tumor.

• Metabolic panel. Evaluates liver and kidney function, which is important for treatment planning.

• Tumor markers. Blood tests for carcinoembryonic antigen and CA 19-9 are sometimes done. These markers can be elevated in some stomach cancers. They are more useful for monitoring response to treatment and detecting recurrence than for initial diagnosis.

• H. pylori testing. Your doctor will check whether you have H. pylori infection, as this information is relevant to your overall stomach health and risk.

Imaging tests

Once stomach cancer has been confirmed, imaging tests help determine whether and how far the cancer has spread. Your doctor will recommend specific tests based on your situation.

• CT scan. A computed tomography scan creates detailed cross-sectional images of the chest, abdomen, and pelvis. CT is the most commonly used imaging test for staging stomach cancer. It can show the size and location of the primary tumor, involvement of nearby organs, enlarged lymph nodes, and distant spread to organs such as the liver and lungs.

• PET-CT scan. A positron emission tomography scan combined with a CT scan shows areas where cells are using large amounts of energy, which can indicate cancer. PET-CT is used in some patients to look for spread to lymph nodes and distant sites that may not be seen on CT alone. It is less reliable for diffuse-type stomach cancer than for intestinal-type.

• Endoscopic ultrasound. An ultrasound probe attached to an endoscope allows your doctor to look at the layers of the stomach wall from inside the stomach and assess nearby lymph nodes. Endoscopic ultrasound is particularly useful for determining how deeply the cancer has grown into the stomach wall, which is important for staging and for deciding whether minimally invasive endoscopic treatment is possible.

• MRI scan. Magnetic resonance imaging is sometimes used to evaluate the liver or other organs for possible spread, particularly when CT results are unclear.

• Diagnostic laparoscopy. A surgical procedure in which a camera is inserted through a small incision in the abdomen to directly view the stomach and surrounding structures. It is often done before major surgery to check for spread to the lining of the abdominal cavity that might not be visible on CT.

Biomarker and molecular testing

Testing the tumor for specific molecular features is now a standard and essential part of stomach cancer diagnosis. The results guide treatment decisions, particularly for advanced disease:

• HER2 testing. HER2 is a protein that promotes cancer cell growth. About 15 to 20 percent of stomach adenocarcinomas have too many copies of the HER2 gene or too much HER2 protein. Stomach cancers that are HER2-positive can be treated with trastuzumab, a targeted therapy that blocks HER2. All advanced stomach adenocarcinomas should be tested for HER2.

• PD-L1 testing. Measures a protein on tumor cells that can indicate whether the cancer is likely to respond to checkpoint inhibitor immunotherapy. The combined positive score is the measure most often used for stomach cancer.

• Mismatch repair and microsatellite instability testing. Checks for defects in a DNA repair system. Stomach cancers that are mismatch repair deficient or microsatellite instability-high respond well to pembrolizumab and other checkpoint inhibitors. About 10 to 15 percent of stomach cancers have this feature.

• FGFR2b testing. A newer biomarker relevant to selected stomach cancers. Drugs targeting FGFR2b are being evaluated in clinical trials and have received regulatory approval in some settings.

• Next-generation sequencing. A broad test that looks for mutations in many cancer-related genes at once and can identify additional targets for treatment.