Tests will be performed to investigate symptoms of stomach cancer and confirm a diagnosis. Some of the more common tests include: 

• a physical examination 
• blood test to look for anaemia and to check for organ function such as liver function tests 
• examination of a stool sample, to check for blood 
• examination of the inside of the stomach and other parts of the upper digestive system using an endoscope (a thin tube with a light on the end of it) – this may also be called a gastroscopy 
• taking a sample of tissue (biopsy) from the stomach wall for examination under a microscope. A biopsy is usually taken during an endoscopy and can be guided by endoscopic ultrasound or computerised tomography (CT). The tissue sample may be checked to see if there are changes to the HER2 protein, the PD-L1 protein, or a marker called microsatellite instability (MSI) – this process is called molecular testing, and can let your doctor know if targeted therapy or immunotherapy drugs would be suitable for you. 

Staging^[2]

If you are diagnosed with stomach cancer, you might have more tests to determine the stage of the disease and whether the cancer has spread to other parts of the body. These can include: 

• imaging tests, such as an endoscopic ultrasound, CT scans, positron emission tomography (PET-) CT scans or magnetic resonance imaging (MRI) 
• a type of surgery called a laparoscopy (also known as ‘keyhole’ surgery). 

Knowing the stage of the disease helps your medical team plan the best treatment for you. 

Stomach cancer is often staged using the TNM (tumour, node, metastasis) system. Numbers (or scores) are given to the size of the tumour, whether or not lymph nodes are affected, and whether the cancer has spread. Higher scores mean that the cancer is more advanced. These scores are combined to work out the overall stage of the cancer. 

Stomach cancer is divided into 4 stages, depending on its thickness in the stomach wall and whether it has spread to nearby lymph nodes or other organs: 

• Stage 1, or early stomach cancer, is where tumours are found only in the stomach lining 
• Stage 2–3, or locally advanced stomach cancer, is where tumours have spread deeper into the layers of the stomach wall and to nearby lymph nodes 
• Stage 4, or advanced or metastatic stomach cancer, is where tumours have spread beyond the stomach wall to nearby lymph nodes or parts of the body, or to distant lymph nodes and parts of the body.