Diagnostics tests explained
Diagnostic testing will help your doctor understand the specifics of your tumor type, classify your tumor grade and cancer stage, develop the best possible treatment plan for you, and monitor your health and the effects of your treatment. In this section, you will find information about the most common tests that may be performed for diagnosing and monitoring NET.
Biopsy
A biopsy is a procedure where a small piece of tissue from the suspected tumor is removed (either through endoscopy or surgery) and analyzed in a pathology laboratory. Using immunohistochemistry, a pathologist usually tests the tumor tissue for specific biomarkers, such as chromogranin A. This type of test uses antibodies linked to a dye, which helps the pathologist view the tissue under a microscope and obtain specific information about the tumor cells.
The pathology report is critical for oncologists to decide on the most suitable management strategy for your type of cancer. There are different types of biopsies, and you and your doctor may discuss which type is right for you.
Blood tests
Doctors look for signs of increased levels of NET biomarkers, including specific proteins and hormones that may help determine what type of NET is present. Blood tests may look at kidney function (urea and electrolytes), liver function, thyroid function, pituitary hormones (e.g., prolactin, growth hormones), serum calcium, chromogranin A or plasma metanephrines among others.
Urine tests
Functional NET tumors generally produce high levels of serotonin, a chemical that breaks down and generates 5-HIAA. 5-HIAA is excreted into the urine. To test for 5-HIAA, you may be asked to provide urine samples collected over 24 hours because serotonin levels go up and down throughout the day. You may be asked to avoid certain medications, including over-the-counter medicines, 3 to 7 days before the test and some foods rich in serotonin (e.g., chocolate, olives and bananas).
Endoscopy
Endoscopy is a medical procedure usually done under sedation. Small pieces of suspicious tissue can be removed and analyzed during the endoscopy at the pathology lab. Depending on the location and type of tumor, the doctor may use one of the following procedures:
Gastroscopy or colonoscopy: Using a thin, flexible fiber-optic tube called an endoscope, which is inserted down the esophagus and into the stomach (gastroscopy) or into the colon via the rectum (colonoscopy), the doctor can examine different parts of your digestive tract.
Bronchoscopy: A narrow, flexible fiber-optic tube called a bronchoscope is inserted down the throat and into the airway to see the trachea and lungs.
Endoscopic ultrasound: This test allows one to look at the digestive tract and surrounding organs (e.g., the pancreas) with a flexible camera with ultrasound capabilities, which can help pick up small tumors that might not be visible on other scans.
Radiological imaging
Computed tomography (CT) scans provide a 3D picture of the inside of the body through a series of many cross-section images taken with a highly specialized X-ray machine. The scan usually takes about 5 minutes. Depending on the scan, you may be asked to drink a contrast solution or receive a contrast dye injection, which helps make specific tissues more visible and produces better images of the tumors or other abnormalities.
Magnetic resonance imaging (MRI) scans use magnetic fields to create a signal that a computer processes into a 2D or 3D image. They help detect small tumors and metastases. MRI scans typically take longer than CT scans and are noisier (you may be given earplugs). MRI scans take place in a special machine that can cause some people to feel claustrophobic. If you suffer from claustrophobia or have other concerns, talk to your doctor about receiving additional sedation to help you feel more comfortable. You should not have an MRI if you have any metal parts in your body (such as a pacemaker, bone or tooth implant).
Ultrasound scans use high-frequency sound waves to produce pictures of the inside of the body. They are non-invasive, meaning the test is done entirely outside the body without anything entering it, and the images are captured in ‘real-time’. Ultrasound scans can show the structure and movement of your body’s internal organs and blood flowing through blood vessels.
Nuclear imaging
Nuclear imaging techniques, also known as functional scans, use a small amount of radiodiagnostic agents injected into the bloodstream. These compounds bind to receptors found on the tumor's surface and release a radioactive signal, which can be detected using a scanning device. Nuclear imaging techniques are sensitive and specific in detecting NETs and their metastases.
Positron emission tomography (PET) is increasingly combined with CT scans, known as PET/CT scans, to provide more detailed images.
Gallium-68 or Copper-64 PET scans may be used in patients with NETs expressing somatostatin receptors, a type of cellular receptor that is present in some NETs, and may detect tumors located anywhere in the body that are difficult to detect using MRI or CT scans alone.
18F-FDG PET scans detect cells that rapidly deplete the glucose in your body, which occurs in many types of cancer. Some NETs, particularly aggressive and faster-growing ones, may be detected in this scan.