Application of Octreotide PET/CT in Neuroendocrine Tumors

Author: Shi Xue

Reviewer: Zhao Yinlong

Case 1

The patient was a 60-year-old male who had undergone surgery for gastrointestinal perforation 5 and 4 years ago. He reported that he had undergone multiple gastrointestinal endoscopic examinations and found gastrointestinal ulcers, intermittent mucus and black stools. The clinician suspected the presence of gastrinoma based on the patient's history of repeated ulcer perforation. The patient went to many hospitals and underwent various examinations, but the "culprit" was not found.

PET/CT examination revealed nodules beside the gallbladder, octreotide imaging was positive, and no increased 18F-FDG metabolism was found. Neuroendocrine tumors were considered, and gastrinoma was not excluded.

If the tumor is not removed, gastrointestinal ulcer perforation will inevitably plague the patient again and again. Finding the source can solve the problem once and for all.

Case 2

The patient was a 58-year-old female. Abdominal CT scan revealed multiple lesions in the liver. Metastasis was suspected, so a PET/CT scan was performed to search for the primary lesion.

PET/CT examination revealed presacral soft tissue shadows, multiple liver lesions, and multiple bone destruction. The above lesions were positive for octreotide imaging, and no increased 18F-FDG metabolism was found. Neuroendocrine tumors were considered to be the source. The patient's medical history was traced back to surgery for grade 1 rectal neuroendocrine tumors in 2019. Liver puncture, pathological results indicated grade 2 neuroendocrine tumors.

Neuroendocrine neoplasms (NENs) are a group of heterogeneous tumors that originate from neuroendocrine cells. Neuroendocrine cells are widely distributed in the human body, including the pituitary gland, thyroid gland, parathyroid gland, pancreas, thymus gland, adrenal gland, gastrointestinal tract, etc. NENs can occur in many organs and tissues in the body, with the most common sites being the pancreas and gastrointestinal tract. The clinical manifestations of patients are diverse and complex, and hormone-related clinical symptoms may or may not occur.

Somatostatin receptor is a glycoprotein mainly distributed on the cell membrane of neuroendocrine origin. The biological activity of somatostatin can only be exerted by binding to somatostatin receptor. Under pathological conditions, somatostatin receptors are overexpressed on the surface of 80% of neuroendocrine cells such as gastrointestinal pancreatic neuroendocrine tumors, pituitary adenomas, pheochromocytomas, carcinoids, and medullary thyroid carcinomas. Therefore, somatostatin receptors have become a commonly used imaging target. Somatostatin receptor imaging is the use of radionuclides (99mTc, 68Ga, 18F, 111In, etc.) to label somatostatin analogs. After injection into the body, somatostatin analogs bind to somatostatin receptors on the surface of lesions in the body, and the gamma rays emitted by the radionuclides are received by imaging equipment (SPECT/CT, PET/CT, PET/MR), thereby making the tumor visible. Octreotide is the most widely used somatostatin analog, and octreotide imaging is the most commonly used method for evaluating neuroendocrine tumors. The imaging results can provide prognostic information for neuroendocrine tumors, evaluate the thoroughness of surgery, observe the presence of residual lesions, follow up for recurrence, and help clinicians make treatment decisions.

Octreotide PET/CT imaging is a routine project in the nuclear medicine department. In addition, there are many new imaging agents used for PET/CT imaging, which complement FDG and solve major clinical problems together.