Diagnosing gastric adenocarcinoma involves multiple steps that help doctors understand exactly what is happening inside your stomach and how far the disease may have spread. From initial symptoms that prompt investigation to detailed imaging and tissue analysis, each diagnostic test plays an important role in creating a complete picture of the cancer and guiding treatment decisions.

Introduction: Who Should Undergo Diagnostics

If you experience persistent symptoms related to your digestive system, it may be time to seek medical attention. Gastric adenocarcinoma, which is the most common form of stomach cancer accounting for 90% to 95% of all stomach cancers, often does not cause symptoms in its early stages. This makes it particularly challenging to detect when treatment would be most effective.^[1][2]

You should consider seeking diagnostic testing if you experience symptoms such as low appetite, unintentional weight loss, abdominal pain or discomfort, feeling full after eating only small amounts of food, heartburn that doesn’t go away, indigestion, nausea, vomiting, or abdominal swelling. More concerning signs include bloody vomit or stool, persistent tiredness or weakness, or jaundice (yellowing of the skin), which may indicate the cancer has spread to the liver.^[3][17]

Certain individuals may benefit from earlier or more frequent screening even without symptoms. This includes people with a family history of stomach cancer, those with chronic stomach conditions like gastroesophageal reflux disease or gastritis, individuals with a history of stomach ulcers or polyps, and people with infection by bacteria called Helicobacter pylori (H. pylori). The average age of people diagnosed with stomach cancer is 68, and around 60% of cases occur in patients older than 65, though anyone can develop this disease.^[1][17]

Diagnostic Methods

When a healthcare provider suspects gastric adenocarcinoma, they will use several diagnostic methods to confirm the presence of cancer, determine what type it is, and understand how far it may have spread. The diagnostic process typically begins with a review of your medical history and a physical examination focusing on your abdomen. Your doctor will ask about your symptoms, when they started, and whether you have any risk factors for stomach cancer.^[3]

Upper Endoscopy

The most important test for diagnosing stomach cancer is called an upper endoscopy, also known as an esophagogastroduodenoscopy or EGD. During this procedure, your doctor inserts a thin, flexible tube with a tiny camera and light attached (called an endoscope) through your mouth, down your esophagus, and into your stomach. This allows the doctor to see the inside lining of your stomach directly and look for any unusual areas, tumors, or other abnormalities.^[3][10]

While performing the endoscopy, if the doctor sees anything suspicious, they can take small tissue samples through the endoscope. This procedure is called a biopsy. The tissue samples are then sent to a laboratory where a specialist called a pathologist examines them under a microscope. The pathologist looks for cancer cells and determines what type of cells they are. This information is crucial because it confirms whether cancer is present and helps guide treatment decisions.^[3]

Imaging Tests

Once cancer is confirmed through biopsy, doctors use various imaging tests to see how large the tumor is and whether it has spread beyond the stomach to nearby organs or distant parts of the body. These tests create detailed pictures of the inside of your body without requiring surgery.^[3]

Computed tomography scans, commonly called CT scans, use X-rays taken from different angles to create cross-sectional images of your body. For stomach cancer, CT scans of your chest, abdomen, and pelvis help doctors see if the cancer has spread to nearby lymph nodes or other organs like the liver or lungs. You may need to drink a contrast solution before the scan to make your stomach and intestines show up more clearly on the images.^[3]

Positron emission tomography scans, or PET scans, involve injecting a small amount of radioactive sugar into your vein. Cancer cells tend to absorb more of this sugar than normal cells, so they appear brighter on the scan images. PET scans are particularly useful for detecting cancer that has spread to distant parts of the body. Sometimes, a PET scan is combined with a CT scan in a single procedure called a PET-CT scan, which provides both anatomical and functional information about the tumor.^[3]

Magnetic resonance imaging, or MRI, uses powerful magnets and radio waves instead of X-rays to create detailed images of soft tissues in your body. MRI scans may be used in certain situations to get a better look at the stomach or to check if cancer has spread to the liver or brain.^[3]

Blood Tests

Doctors may order various blood tests as part of the diagnostic process. These tests don’t detect stomach cancer directly, but they provide important information about your overall health and how well your organs are functioning. Blood tests can show if you have anemia (low red blood cell count), which commonly occurs with stomach cancer due to bleeding from the tumor. They can also check your liver and kidney function, which is important information when planning treatment.^[3][10]

Some blood tests look for specific markers that may be elevated in people with stomach cancer. However, these markers are not used alone to diagnose cancer because they can be elevated for many other reasons as well.

Staging and Grading

After the initial diagnostic tests, doctors determine the stage of the cancer, which describes how large the tumor is and how far it has spread. The stage ranges from 0 (very early cancer confined to the stomach lining) to 4 (cancer that has spread to distant organs). Staging helps doctors predict how the cancer might behave and determine which treatments are most appropriate.^[3]

Doctors also assess the grade of the cancer by examining how abnormal the cancer cells look under a microscope. Cells are graded from 1 to 3, with grade 1 cells looking most like normal stomach cells and grade 3 cells looking very abnormal. Higher-grade cancers tend to grow and spread more quickly than lower-grade ones.^[7]

The cancer cells may also be described by their level of differentiation. Well-differentiated cells look and behave more like normal cells and tend to grow slowly. Poorly differentiated or undifferentiated cells look very different from normal cells and typically grow and spread more aggressively.^[7]

Diagnostics for Clinical Trial Qualification

If you’re considering participating in a clinical trial for gastric adenocarcinoma, you will need to undergo additional or more specific diagnostic tests. Clinical trials have strict criteria about who can participate, and these criteria often depend on very specific characteristics of your cancer that must be confirmed through testing.^[9][13]

Molecular and Biomarker Testing

Modern clinical trials increasingly focus on treating cancer based on its molecular characteristics rather than just where it’s located in the body. For gastric adenocarcinoma, several important biomarkers are tested to determine eligibility for specific trials or targeted therapies.^[13]

HER2 testing looks for a protein called human epidermal growth factor receptor 2 on the surface of cancer cells. About 15% to 20% of gastric adenocarcinomas are HER2-positive, meaning they have high levels of this protein. HER2-positive cancers may qualify for clinical trials testing targeted therapies that specifically attack cells with this protein. The test is performed on biopsy tissue using special laboratory techniques.^[9][13]

PD-L1 testing measures the level of a protein called programmed death-ligand 1 on cancer cells and immune cells within the tumor. This protein helps cancer cells hide from the immune system. Tumors with high PD-L1 expression may respond better to immunotherapy drugs, which help the immune system recognize and attack cancer cells. Many clinical trials testing immunotherapy require PD-L1 testing for enrollment.^[9][13]

Microsatellite instability (MSI) testing examines whether the cancer cells have problems with their DNA repair systems. Cancers with high microsatellite instability (MSI-high) or deficient mismatch repair (dMMR) have accumulated many DNA errors. These cancers often respond particularly well to immunotherapy. Between 5% and 20% of gastric adenocarcinomas show MSI-high status, with variation based on ethnic background and tumor location. This test is performed on tumor tissue obtained during biopsy.^[9][13][15]

Epstein-Barr virus (EBV) testing determines if the cancer is associated with this common virus. Between 5% and 10% of gastric adenocarcinomas are EBV-positive. These cancers have distinct characteristics and may respond differently to certain treatments, making EBV status an important factor in some clinical trial eligibility criteria.^[3][15]

Performance Status Assessment

Clinical trials typically require that participants have a certain level of physical function and overall health. Your doctor will assess your performance status using standardized scales that measure your ability to perform daily activities, work, and care for yourself. This assessment helps determine if you’re healthy enough to tolerate the experimental treatment being studied.

Additional Testing Requirements

Depending on the specific clinical trial, you may need additional blood tests to check your blood cell counts, liver function, kidney function, and other organ systems. Some trials require specific imaging tests performed in a particular way or within a certain timeframe before enrollment. You may also need to have adequate tissue samples from your tumor available for research purposes, which might require additional biopsies if the original sample was too small or was fully used for diagnostic testing.^[9]

Clinical trials may exclude people who have received certain prior treatments or who have specific medical conditions in addition to their cancer. Your medical team will review all eligibility criteria with you to determine which trials might be appropriate for your situation. The testing required for clinical trial screening is designed to ensure that the trial results are reliable and that participants are likely to benefit from or safely tolerate the experimental treatment.