The Value of Somatostatin Receptor Scintigraphy (SRS) in Patients with NETG1/G2 Pancreatic Neuroendocrine Neoplasms (p-NENs).

BACKGROUND: Neuroendocrine neoplasms of the pancreas (p-NEN) are common gastro-entero-pancreatic neuroendocrine neoplasms (GEP-NENs). The aim of this retrospective study was to review the of value of Somatostatin Receptor Scintigraphy (SRS) in initial detection of p-NEN, evaluation of tumour extent and as imaging follow-up after radical surgery in patients with confirmed well (NETG1) or moderate (NETG2) differentiated p-NEN based on pathological WHO 2017 classification. MATERIAL AND METHODS: Overall 281 patients with confirmed p-NEN were enrolled. The SRS was performed to evaluation of primary p-NEN, also to assess clinical stage of disease, based on current World Health Organization (WHO) classification and during clinical follow-up. A total of 829 examinations were performed over time in these 281 patients using 99mTc HYNICTOC. Images were acquired between 1 - 3 h after i.v. injection of radiotracer. Initially whole body WB-SPECT and then WB-SPECT/CT, with standard iterative reconstruction were used. RESULTS: There were 159 patients with NETG1 (57%) and 122 subjects with NETG2 (43%). The female to male ratio was 1.1:1. In 68 patients (22%) with NETG1/G2 eight-seven SRS (10%) were performed to confirm initial diagnosis. SRS results were as follow: true positive (TP) = 84 (97%), false negative (FN) = 3 (3%), no true negative (TN) or false positive (FP) results of SRS examination (sensitivity of SRS per patient was 96%). In 198 subjects (66%) SRS was used in evaluation and re-evaluation of the clinical stage, A total of 661 (80%) examinations were carried out in these patients. There were TP=514 (77%), TN=136 (21%), FN=7 (1%) and FP=4 (1%) results. The sensitivity and specificity per patient were: 96% and 95%. The sensitivity and specificity per study: 98% and 97%. In 35 patients (12%) SRS was used as imaging follow-up after radical surgery, there were overall 81 examination (10%) which were performed. There were 76 (91%) TN results of examinations of SRS and in 4 patients we identified recurrence (TP). In total, which consists of initial diagnosis/staging and follow-up patients, the sensitivity of SRS was 96% and specificity 97% per patient and per study sensitivity and specificity was 98%. CONCLUSIONS: SRS using 99mTc HYNICTOC acquired in WB-SPECT or WB-SPECT/CT techniques is an excellent imaging modality in detection of primary NETG1/G2 p-NEN. Our study confirms that SRS has high sensitivity and specificity, as a result has tremendous value as an examination method to assess clinical stage of disease and as an imaging follow-up after radical treatment.

Peptide Receptor Radionuclide Therapy for Advanced Gastroenteropancreatic Neuroendocrine Tumors - from oncology perspective.

Peptide Receptor Radionuclide Therapy (PRRT) is a form of molecular targeted therapy which is performed by using a small peptide (somatostatin analogue - SSA) that is coupled with a radionuclide beta emitting radiation. PRRT is a nuclear medicine for the systemic treatment of non-resectable, metastasized well/moderately differentiated, neuroendocrine tumours (NET) with overexpression of somatostatin receptor. These types of tumours include gastroenteropancreatic neoplasm (GEP-NENs), e.g. arising from the small bowel (often called carcinoid tumours), the pancreas, duodenum or stomach, but also from the large bowel or the lung and many other tissues (so called diffuse neuroendocrine system). The goal of PRRT is irradiation of tumour cells, via direct binding into specific receptor, somatostatin receptors (SSTR) family, overexpressed on the cell membrane of the primary tumours as well as on the metastasis. Over many years of clinical use of PRRT with 9°Y and current with ¹77Lu DOTA conjugated somatostatin analogues proved to be efficient therapy option for NETs, with tumour responses, base on radiological evaluation. Also, a clinical response with symptoms relief and improvement in quality of life based on standard EORTC questioners is seen. Additional, common NET biomarker reduction and, ultimately, an impact on overall survival (OS) of patients with advanced non-resectable often progressive NEN can be expected. PRRT with 9°Y or ¹77Lu-labelled peptides is generally well tolerated by most of the patients. The acute side effects (Adverse Events - AEs) are usually mild; most of them are related to the co-administration of amino acids (AA), such as nausea and vomiting. Others are related to the radioisotopes, such as fatigue or the exacerbation of endocrine syndromes, which are very rarely and they occurs, only in patients with functional tumours and large tumours burden. Chronic and permanent damage has an effect on target organs, particularly the kidneys and the bone marrow, which are generally mild. Currently, when ¹77Lu DOTATATE is used, the potential risk to kidney damage is significantly reduced, compared to the previous usage of 9°Y labelled analogues. Up to now, kidney and bone marrow toxicity limits the dose of radioactivity of PRRT.