Quantitative digital image analysis of somatostatin receptor 2 immunohistochemistry in pancreatic neuroendocrine tumors

Somatostatin Receptor 2 in 10 Different Types of Human Non-Neoplastic Gastrointestinal Neuroendocrine Cells

Somatostatin is known to inhibit the secretion of various hormones by acting on endocrine cells through the somatostatin receptor 2 (SSTR2). Immunohistochemical evaluation of SSTR2 has become increasingly important in clinical practice to determine treatment strategies for patients with a neuroendocrine tumor (NET). Gastrointestinal (GI) tracts contain various neuroendocrine cells that constitute a diffuse endocrine system and some NETs are derived from those cells. In addition, NETs have been well known to express a variable spectrum of proteins shared by their normal cell counterparts of the specific anatomical sites. Thus, we may derive the kinetics of SSTR2 expression of NETs, including de novo expression, from the SSTR2 expression of the corresponding normal neuroendocrine cells. Therefore, a detailed study on the distribution of SSTR2 in normal human neuroendocrine cells may contribute to understanding the expression of SSTR2 in GI-NETs. However, the detailed cellular localization of SSTR2 in non-neoplastic neuroendocrine cells remains unknown. Therefore, we immunolocalized SSTR2 in neuroendocrine cells of normal human GI tracts, including the stomach, duodenum, ileum, and rectum, obtained from 41 surgically resected tissue specimens. Double immunohistochemistry of SSTR2 and hormones or hormone-associated proteins was performed. In all GI neuroendocrine cells, cell types other than D- and EC-cells demonstrated a high percentage of SSTR2-positive cases or a high double-positive ratio. In particular, EC-cells showed lower SSTR2-positive ratios in all sites. Midgut NETs, which often produce serotonin, are excellent targets for somatostatin analogs and are positive for SSTR2. Thus, we speculated that EC-cell NETs might lead to the de novo expression of SSTR2. In addition, a previous report showed high SSTR2 expression in ECL-cell NETs and gastrinomas, which could be because they are derived from neuroendocrine cells with high SSTR2 expression. This study may contribute to understanding the expression of SSTR2 in GI-NETs.

Digital quantification of somatostatin receptor subtype 2a immunostaining: a validation study

OBJECTIVE

The aim of this study was to develop an open-source and reproducible digital quantitative analysis (DIA) of somatostatin receptor subtype 2a (SST2) staining in formalin-fixed paraffin-embedded tissues of pancreatic neuroendocrine tumors (panNETs) and growth hormone (GH)-secreting pituitary adenomas (GHomas).

DESIGN

SST2 immunostaining of 18 panNETs and 39 GHomas was assessed using a novel DIA protocol and compared with a widely used semi-quantitative immunoreactivity score (IRS).

METHODS

The DIA software calculates the staining intensity/area and the percentage of positive cells (%PC). Four representative images were selected for each sample by two independent selectors (S1 and S2), with the analysis performed by two independent analyzers (A1 and A2). Agreement between observers was calculated using the concordance correlation coefficient (CCC).

RESULTS

In panNETs, the CCC ranged 0.935-0.977 for intensity/area and 0.942-0.983 for %PC. In GHomas, the CCC ranged 0.963-0.997 for intensity/area and 0.979-0.990 for %PC. In both panNETs and GHomas, the DIA staining intensity was strongly correlated with the IRS (Spearman rho: 0.916-0.969, P < 0.001), as well as the DIA %PC with the IRS %PC (Spearman rh: 0.826-0.881, P < 0.001). In GHomas, the biochemical response to somatostatin receptor ligands correlated with SST2 expression, evaluated both as DIA intensity/area (Spearman rho: -0.448 to -0.527, P = 0.007-0.004) and DIA %PC (Spearman rho: -0.558 to -0.644, P ≤ 0.001).

CONCLUSIONS

The DIA has an excellent inter-observer agreement and showed a strong correlation with the widely used semi-quantitative IRS. The DIA protocol is an open-source, highly reproducible tool and provides a reliable quantitative evaluation of SST2 immunohistochemistry.

Mixed neuroendocrine–nonneuroendocrine neoplasms of the gastrointestinal system: An update

Mixed neuroendocrine-nonneuroendocrine neoplasms (MiNENs) of the digestive tract are a rare heterogeneous group of tumors that present many challenges in terms of diagnosis and treatment. Over the years, the diagnostic criteria, classification, and clinical behavior of these tumors have been the subjects of ongoing debate, and the various changes in their nomenclature have strengthened the challenges associated with MiNENs. This review is performed to provide an understanding of the key factors involved in the evolution of the designation of these tumors as MiNEN, highlight the current diagnostic criteria, summarize the latest data on pathogenesis and provide information on available treatments. Moreover, this work seeks to increase the awareness about these rare neoplasms by presenting the clinicopathological features and prognostic factors that play important roles in their behavior and discussing their different regions of origin in the gastrointestinal system (GIS). Currently, the MiNEN category also includes tumors in the GIS with a nonneuroendocrine component and epithelial tumors other than adenocarcinoma, depending on the organ of origin. Diagnosis is based on the presence of both morphological components in more than 30% of the tumor. However, this value needs to be reconfirmed with further studies and may be a limiting factor in the diagnosis of MiNEN by biopsy. Furthermore, available clinicopathological data suggest that the inclusion of amphicrine tumors in the definition of MiNEN is not supportive and warrants further investigation. The diagnosis of these tumors is not solely based on immunohistochemical findings. They are not hybrid tumors and both components can act independently; thus, careful grading of each component separately is required. In addition to parameters such as the metastatic state of the tumor at the time of diagnosis and the feasibility of surgical resection, the aggressive potential of both components has paramount importance in the choice of treatment. Regardless of the organ of origin within the GIS, almost MiNENs are tumors with poor prognosis and are frequently encountered in the elderly and men. They are most frequently reported in the colorectum, where data from molecular studies indicate a monoclonal origin; however, further studies are required to provide additional support for this origin.

Somatostatin Receptor 2 Expression Profiles and Their Correlation with the Efficacy of Somatostatin Analogues in Gastrointestinal Neuroendocrine Tumors

Simple Summary

Immunolocalization of somatostatin receptor 2 (SSTR2) could predict the therapeutic efficacy of somatostatin analogues (SSAs) in neuroendocrine tumors (NETs). Therefore, in this study, we evaluated SSTR2 immunoreactivity and elucidated its correlation with clinicopathological variables, including the therapeutic response to SSAs in gastrointestinal neuroendocrine tumors (GI-NETs) using digital image analysis (DIA) and other established methods of evaluation. SSTR2 immunoreactivity in foregut NETs was significantly higher than that in hindgut NETs. SSTR2 immunoreactivity was significantly negatively correlated with the Ki-67 labeling index in foregut NETs but positively correlated in hindgut NETs. Therefore, the significance of SSTR2 immunoreactivity in GI-NETs is considered to be different according to the primary sites. We also first demonstrated that DIA could provide a good alternative for predicting response to SSAs in evaluating SSTR2 immunoreactivity of GI-NETs.

Abstract

Somatostatin analogues (SSAs) are widely used to treat gastroenteropancreatic neuroendocrine tumors (GEP-NETs). Somatostatin receptor 2 (SSTR2) immunoreactivity serves as a predictive marker of the therapeutic efficacy of SSAs in pancreatic NETs. However, SSTR2 expression profiles in tumor cells and their association with the therapeutic efficacy of SSAs remains virtually unknown in gastrointestinal NETs (GI-NETs). Therefore, we evaluated the association between SSTR2 immunoreactivity and embryological origin and proliferative activity in 132 resected surgical tissues of GI-NETs. The correlation between SSAs’ therapeutic efficacy and SSTR2 immunoreactivity was evaluated in 14 GI-NETs treated with SSAs. SSTR2 immunoreactivity was evaluated using Volante scores, immunoreactive scores, and digital image analysis (DIA). SSTR2 immunoreactivity was significantly negatively and positively correlated with the Ki-67 labeling index in foregut and hindgut NETs, respectively. In the normal mucosa, neuroendocrine cells in the rectum had significantly lower positive rates of SSTR2 than those in the stomach and duodenum. SSTR2 expression profiles in GI-NETs could differ by primary sites, while the difference of those between foregut and hindgut NETs might be derived from the SSTR2 status of normal neuroendocrine cell counterparts. In addition, DIA could provide a good alternative for predicting response to SSAs in evaluating SSTR2 immunoreactivity of GI-NETs.