Diagnosis of Neuroendocrine cancer

Summary

The diagnosis of neuroendocrine tumors (NETs) involves the combined diagnostic result of pathology test, biochemistry test, hormonal tests, diagnostic imaging and endoscopic imaging in order to get a comprehensive clinical picture.

Introduction

The neuroendocrine tumors (NETs) diagnosis requires coordinated, multidisciplinary action involving oncologists, interventional radiologists, surgeons, and also pathologists. However, the results of pathology tests, diagnostics, hormonal tests, and functional imaging come together to form a comprehensive clinical picture.

Pathology

Tissue collection is indeed essential for NET diagnostics, pathological examination. In fact, if surgical resection is not possible, a doctor should prefer core needle biopsy over fine-needle aspiration to assess tumor structure fully^​1,2​.

Syndrome-specific biochemical testing

In patients with presenting NET symptoms, biochemical tests indeed target a specific syndrome. Significantly, a 24-hour urinary 5-hydroxyindole acetic acid (5-HIAA) test should be recorded in patients with small bowel masses or symptoms suggestive of carcinoid syndrome. However, the sensitivity of this test is around 35-73%^​3,4​. Patients should avoid eating foods rich in serotonin (such as pineapples, bananas, kiwis, avocados, or nuts) before three days of testing.

Nonsyndrome-specific biochemical testing

While Chromogranin A is the NET diagnostic marker of choice;^​5​ it has high sensitivity (53%–91%) but low specificity (<50%). For example, the reasons for false elevations include obstructive, renal failure, adenocarcinoma, proton-pump inhibitors and severe arterial hypertension^​6​.

Diagnostic imaging

Altogether, there are two general types of diagnostic imaging modalities used in conjunction with NET diagnostics.

The first method is standard cross-sectional imaging which the doctors do particularly by using magnetic resonance imaging (MRI) or computed tomography (CT). In fact, the Canadian consensus guidelines suggest that all patients with suspected NETs should have chest, abdominal, and pelvic CT scans to determine the stage and consider an MRI of the liver or pancreas if a more detailed definition is needed^​1,2​.

However, the second method is functional imaging using overexpression of normal somatostatin receptors in NETs. While the radiolabeled somatostatin analog is administered intravenously and is focused on the NET, the radiation emitted is detected to localize the tumor. 111Indium (In)-labelled pentetreotide- is a commonly used radioactive tracer in Canada. in fact, a recent meta-analysis of NET molecular imaging methods showed that scintigraphic imaging of 111 In-label pentetreotide somatostatin receptors with 46–100% sensitivity for abdominal NET, 46–83% for pancreatic NET and 71% for bronchial NET^​7​.

The new radioactive isotope 68Ga (gallium) is a positron emitter that not only can be attached to somatostatin analogs, but also localized by positron emission tomography (PET)/CT imaging. Therefore, NETs were imaged using 111In-label pentoxide scanning and 68Ga-DOTATATE PET/CT^​8​. The sensitivity of 68Ga-DOTATATE PET/CT compared to 111In-labeled pentoxide was 96% (95%CI= 86%-100%) versus 72% (95% CI= 58%-84%). Access to 68Ga-based imaging is currently limited in specialized centres in Canada but is expected to become widespread soon.

It is important to note that imaging methods based on somatostatin analogs have low sensitivity in poorly differentiated cancers, as cells often lack somatostatin receptors. Thus, poorly differentiated tumors can be better characterized by fluorodeoxyglucose (18FDG) PET/CT scanning, which localizes the tumor by uptake of radiolabeled glucose molecules^​8​.

Endoscopic imaging

Indeed, Endoscopic ultrasound is a very sensitive test for diagnosing pancreatic NETs (sensitivity 82%–93%)^​9​. It is beneficial for identifying tumors smaller than 2 cm and localizing insulinomas.

References