Diagnostic Testing

There are different imaging methods available for doctors to learn about a tumor’s size and location before performing surgery. This is a key step in diagnosing cancer. Accurate staging of gastric cancer using the TNM system before surgery is very important. It helps the surgeon know what treatment is best for the patient.

What is the TNM System? Why is it important?

• Tumor (T), Node (N), Metastasis (M). This is a standardized “code” that is used by to describe how severe a tumor is based on some of its features. Describing a tumor in this way is called “staging”.
• T Stage: there are 4 layers of tissue that make up the stomach. They are the:
  • mucosa (T1)
  • submucosa (T2)
  • muscularis (T3)
  • adventitia (T4).
  • The mucosa is the innermost layer, so a tumor that started inside the stomach and has only spread to this shallow layer is the least severe – this is a T1 tumor. The “T” number tells us how deep into the stomach the tumor has grown.
• N Stage: This number describes the number of lymph nodes (LN) that have cancer cells growing in them.
  • N0 – None
  • N1 – 1-2
  • N2 – 3-6
  • N3 – 7 or more
• M Stage: metastasis means the cancer cells have spread from the stomach (the original site) to a distant secondary site, such as another organ.
  • M0 – no metastasis to a distant site
  • M1 – metastasis to a distant site has happened
• Not all tumors can be treated the same way! By understanding the TNM classification of a disease, your doctor can decide the best way to treat it. For example, many cancers that have metastasized (M1) cannot be cured with a gastrectomy.

What is Diagnostic Imaging?

• Diagnostic (or Medical) Imaging refers to the methods and machines that use pictures to get a better look at (diagnose) a patient’s disease. Diagnostic Imaging is used before a patient gets treatment so the doctors can understand the extent of the cancer.  
• Some common diagnostic imaging  modalities that might be used to stage gastric cancer include:
  • Endoscopic Ultrasound (EUS): a thin tube is inserted into the mouth down to the stomach. The tip of the tube has a small probe that releases energy waves (ultrasound). This produces a detailed image of the surrounding area. This is a short, minimally-invasive procedure. Usually the patient is given medicine to help them relax.
  • Abdominal Ultrasound (AU): a handheld probe releasing high energy soundwaves (ultrasound) can create a picture of the internal organs by rubbing it gently over gel applied to the skin. This is different from EUS because it is done outside the body.
  • Magnetic Resonance Imaging (MRI): a full-body scan which uses a strong magnetic field to align the particles inside your body. The energy released by these particles is detected using radio waves. This creates a picture which can show structures inside the body.
  • Computed Tomography (CT): a full-body scan which uses X-ray pictures taken from all angles to create a cross-sectional picture of the inside of the body.
  • Positron Emission Tomography (PET): this allows your doctor to look for something wrong happening in your body. A radioactive tracer is swallowed or injected. Your doctor can see the path of the material through your body, and see if any cells are behaving abnormally.
  • Diagnostic Laparoscopy (DL): a tube with a tiny camera is passed into the belly through a small slit. The camera has a live video feed that shows the doctor what the inside of the body looks like.

Research

These three papers authored by Dr. Coburn and her colleagues all address the subject of diagnostic testing in gastric cancer. They are trying to understand the best way to accurately diagnose a tumor, and what this can mean for how it is treated.