Expression of PD-1 and PD-L1 in poorly differentiated neuroendocrine carcinomas of the digestive system: a potential target for anti-PD-1/PD-L1 therapy

Epidemiology, prognostic factors, and survival analysis in small cell esophageal carcinoma: A population-based study with external validation

Small cell esophageal carcinoma (SCEC) is a poorly differentiated esophageal neuroendocrine neoplasm with a poor prognosis. This study aimed to explore the factors and treatment approaches influencing the prognosis of SCEC. In this retrospective study, we collected data from the 18 Surveillance, Epidemiology, and End Results (SEER) registries cohort between 2004 and 2019, as well as from a Chinese institutional registry covering the period from 2012 to 2022. We assessed the annual percentage change (APC) in incidence of SCEC. Kaplan-Meier and Cox regression analyses were conducted to evaluate survival outcomes. Additionally, nomograms were developed for overall survival (OS) and cancer-specific survival (CSS) in the SEER cohort for SCEC and validated in an independent Chinese cohort. This analysis included 299 SCEC patients from the SEER cohort and 66 cases from the Chinese cohort. During the period of 2004-2019, the incidence of SCEC reached a plateau, with an APC of -1.40 (95% confidence interval [CI]: -4.3 to 1.40, P > 0.05). Multivariable Cox regression analysis revealed that age, distant metastasis, and chemotherapy were independent factors for OS, while distant metastasis and chemotherapy were independent factors for CSS. The nomograms developed for OS and CSS in SCEC exhibited remarkable accuracy and reliable predictive capacity in estimating 1-year, 3-year, and 5-year OS and CSS. SCEC is a rare malignancy with aggressive behavior. Distant metastasis is significantly associated with worse OS and CSS in patients with SCEC. Currently, chemotherapy remains the primary treatment approach for SCEC.

Regorafenib plus avelumab in advanced gastroenteropancreatic neuroendocrine neoplasms: a phase 2 trial and correlative analysis

Gastroenteropancreatic neuroendocrine neoplasms (GEP-NENs) are heterogeneous tumors with limited treatment options. This phase 2 Bayesian study evaluated the combination of regorafenib, a multikinase inhibitor, and avelumab, a programmed death 1 (PD1) ligand 1 inhibitor, in advanced grade 2-grade 3 well-differentiated GEP neuroendocrine tumors or grade 3 GEP neuroendocrine carcinomas after progression on prior therapies. A total of 47 participants were enrolled and 42 were evaluable for efficacy. Participants received regorafenib (160 mg per day) and avelumab (10 mg kg-1 biweekly) in 28-day cycles. The primary endpoint, 6-month objective response rate per the response evaluation criteria in solid tumors version 1.1, was 18% (95% confidence interval (CI): 8-31%), with a median progression-free survival of 5.5 months (95% CI: 3.6-8). Durable responses were noted (16.6 months; 95% CI: 3.7-no response). Treatment-related adverse events were manageable, with fatigue, diarrhea and palmar-plantar erythrodysesthesia being most common. Exploratory biomarker analysis identified PD1 and indoleamine 2,3-dioxygenase 1 expression and activity as potential resistance markers. These findings highlight the clinical potential of regorafenib and avelumab in GEP-NENs, emphasizing the need for predictive biomarkers and validation in future randomized trials. Clinical Trial registration: NCT03475953 .

Basic science and translational implications of current knowledge on neuroendocrine tumors

Neuroendocrine tumors (NETs) are a diverse group of malignancies that can occur in various organs, with a notable prevalence in the lungs and gastrointestinal tract, which are the focus of this Review. Although NETs are rare in individual organs, their incidence has increased over recent decades, highlighting the urgent need for current classification systems to evolve by incorporating recent advances in the understanding of NET biology. Several omics studies have revealed molecular subtypes, which, when integrated into existing classification frameworks, may provide more clinically relevant insights for patients with NETs. This Review examines recent progress in elucidating the biology of NETs, with a particular emphasis on the tumor microenvironment and cells of origin. The existence of different cells of origin, which may contribute to distinct molecular groups, along with profiles of immune infiltration - despite being generally low - could explain the emergence of more aggressive cases and the potential for metastatic progression. Given the molecular heterogeneity of NETs and the diversity of their microenvironments and different cells of origin, there is an urgent need to develop morphomolecular classification systems. Such systems would make it possible to better characterize tumor progression, identify new therapeutic targets, and, ultimately, guide the development of personalized therapies.

PD-L1 expression, tumor-infiltrating lymphocytes, and mismatch repair proteins status in digestive neuroendocrine neoplasms: exploring their potential role as theragnostic and prognostic biomarkers

Theragnostic biomarkers are still needed to select patients with digestive neuroendocrine neoplasms (NENs) for an optimal management. The PD-1/PD-L1 pathway plays a pivotal role in T cells activation and host immune response to cancer and PD-L1 expression in tumor and/or immune cells is used to identify patients who would benefit of treatment with immune checkpoint inhibitors. However, its role as a biomarker is still unclear in digestive NENs. We investigated PD-L1 expression in 68 well-characterized digestive NENs (32 NETs, 32 NECs and 4 MiNENs) and TPS and CPS scores were calculated. In addition, tumor infiltrating T-lymphocytes and mismatch repair protein expression (MMR) were evaluated. All results were correlated with clinicopathological features. PD-L1 expression was higher in NECs than in NETs: TPS > 1% and/or CPS > 1 were observed in 16% of NETs, 68.8% of NECs and 50% of MiNENs (p: 0.05). The mean TPS score in positive cases was 6.3% in NETs, 16.2% in NECs and 5% in MiNENs. The CPS score was 4.8 in NETs, 8.1 in NECs and 6 in MiNENs. MMR-deficient neoplasms were more frequently observed in NECs than in NETs (p: < 0.05) as well as intra-tumor immune infiltration (p: 0.00001). No correlation between PD-L1 expression and survival or other clinicopathological parameters was observed. Our results suggest that treatment with immune checkpoint inhibitors may have a potential role only in selected cases, mainly in NECs and MiNENs.

Gastroenteropancreatic neuroendocrine neoplasms: epidemiology, genetics, and treatment

The incidence of gastroenteropancreatic neuroendocrine neoplasms (GEP NEN) is increasing at a rapid pace and is becoming an increasingly important consideration in clinical care. Epidemiological data from multiple countries indicate that the incidence of gastroenteropancreatic neuroendocrine neoplasms (GEP NEN) exhibits regional, site-specific, and gender-based variations. While the genetics and pathogenesis of some GEP NEN, particularly pancreatic NENs, have been investigated, there are still many mechanisms that require further investigation. The management of GEP NEN is diverse, but surgery remains the primary option for most cases. Peptide receptor radionuclide therapy (PRRT) is an effective treatment, and several clinical trials are exploring the potential of immunotherapy and targeted therapy, as well as combination therapy.

Colorectal neuroendocrine carcinoma and mixed neuroendocrine-non-neuroendocrine neoplasm: Prognostic factors and PD-L1 expression

Colorectal neuroendocrine carcinoma (NEC) and mixed neuroendocrine-non-neuroendocrine neoplasm (MiNEN) are rare malignancies with unclear boundaries and poor prognoses. Our study aimed to conduct a comparative analysis of these diseases, identify prognostic factors, and explore potential therapeutic targets. We collected and analyzed clinicopathological data of NEC and MiNEN in our hospital from 2011 to 2020. Immunohistochemical staining for PD-L1, BRAF V600E, and mismatch repair proteins was performed. We identified 14 NEC and 7 MiNEN cases. Demographic data, including median overall survival (17.1 months for NEC and 18.5 months for MiNEN), did not significantly differ. NEC showed a higher tendency to occur in the rectum and sigmoid colon (p = 0.025) and had fewer cases with metastatic adenocarcinoma components in lymph nodes (p = 0.009) compared to MiNEN. Adverse prognostic factors were age ≥70 years (p = 0.012), N2 nodal status (p = 0.032), and stage IV disease (p = 0.013) based on multivariate Cox regression analysis. We identified five PD-L1 positive cases, two BRAF V600E mutated cases, and one Lynch syndrome case with MSH2 and MSH6 loss. Patients with colorectal NEC or MiNEN exhibited poor survival rates. Adverse prognostic factors included older age, N2 nodal status, and distant metastasis. Potential therapeutic avenues such as immune checkpoint and BRAF inhibitors were suggested for patients with these carcinomas.

Case Report: Gastrointestinal neuroendocrine carcinoma with SMARCA4 deficiency: a clinicopathological report of two rare cases

BACKGROUND

Gastrointestinal neuroendocrine carcinoma (GI NEC) is a rare but highly malignant neoplasm with an aggressive clinical course. SMARCA4 is one of the subunits of the SWI/SNF chromatin remodeling complex. SMARCA4 deficiency can occur rarely in subsets of NECs. Reports of the clinicopathological features of GI NECs with SMARCA4 deficiency are limited.

METHODS

In this study, we retrospectively reported two rare cases of GI NEC with SMARCA4 deficiency and described the clinicopathological, radiographic and histopathological features.

RESULTS

Case 1 was a 43-year-old male with a stage cT3NxM1, IV tumor. Case 2 was a 64-year-old female with a stage cT4aN1M0, IIIA tumor. Both tumors presented as ulcerated masses with infiltration. Pathological examination indicated a solid architecture with poorly differentiated morphology, and complete loss of SMARCA4 (BRG1) was found. Immunohistochemical staining showed positivity for Syn, CgA and CD56. The Ki-67 index was 90% and 70%, respectively. None of the cases had mismatch repair (MMR) deficiency. Case 1 received treatment with chemotherapy and anti-PD-1 immunotherapy. He did not respond to treatment, and died 9 months later. Case 2 received neoadjuvant chemotherapy before surgical treatment, and the tumor showed TRG3 in response to neoadjuvant chemotherapy, chemotherapy and anti-PD-1 immunotherapy were continued after surgical resection. There was no evidence of disease for 10 months.

CONCLUSIONS

GI NEC with SMARCA4 deficiency is a rare entity of gastric NEC. SMARCA4 may be a promising targetable and prognostic biomarker. BRG1 immunohistochemical staining could be performed for GI NECs. Further studies with a larger cohort will be needed.

Defining Tumor Microenvironment as a Possible Target for Effective GEP-NENs Immunotherapy-A Systematic Review

Neuroendocrine neoplasms (NENs) are a heterogenous and recurrent group of malignancies originating from neuroendocrine secretory cells diffused on all parts of the human body. Gastro-entero-pancreatic neuroendocrine tumors (GEP-NETs) account for most NENs. Considering the abundance of possible origins, locations, and tumor specifications, there is still no consensus about optimal treatment options for these neoplasms. In light of the escalating immunotherapeutic approaches, it is crucial to define indications for such therapy in GEP-NETs. Bearing in mind the significance of pathophysiological mechanisms and tumor microenvironment (TME) impact on carcinogenesis, defining TME structure and correlation with the immune system in GEP-NETs appears essential. This paper aimed to assess the characterization of the tumor immune microenvironment for a better understanding of the possible therapeutic options in GEP-NETS. The authors performed a systematic review, extracting papers from the PubMed, Web of Science, and Scopus databases according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Among 3800 articles identified through database searching, 292 were assessed for eligibility. Ultimately, 28 articles were included in the qualitative synthesis. This paper sums up the research on the immune cell infiltrates, immune checkpoint expression, cytokine profile, neoangiogenesis, and microbiome in the TME of GEP-NETs.

Correlation of Neuroendocrine Differentiation with a Distinctively Suppressive Immune Microenvironment in Gastric Cancer

INTRODUCTION

Neuroendocrine neoplasms (NENs) harbored significantly suppressive tumor immune microenvironments (TIMEs). However, the immunological effects of neuroendocrine differentiation (NED) on non-NENs, such as gastric cancer (GC), were unknown.

METHODS

Between pure gastric cancer (PGC) and GC-NED, TIME features were scored based on expression data and validated on serial whole-tissue sections of surgical samples, with tertiary lymphoid structures (TLSs) and the extra-TLS zone evaluated independently using multi-marker immunohistochemical staining. Risk analyses of TIME features on tumor behaviors were performed in GC-NED. The universal immunological effects of NED were explored preliminarily in adenocarcinomas arising in other organs.

RESULTS

Based on over 11,500 annotated TLSs and 2,700 extra-TLS zones, compared with PGC, GC-NED harbored a distinctively more suppressive TIME characterized by increased but immature TLSs, with higher naïve B-cell and follicular regulatory T-cell densities and downregulated TLS maturation-related cell ratios inside TLSs; increased naïve B-cell and regulatory T-cell densities; and a high proportion of exhausted T cells in the extra-TLS zone. The upregulated tumor PD-L1 expression and its close correlations with TLS formation and maturation were remarkable exclusively in GC-NED. TIME features, especially those regarding TLSs, were significantly correlated with tumor growth and invasion. The desynchrony between TLS formation and maturation and increased naïve or regulatory immune cell infiltration was observed in adenocarcinomas of the colorectum, pancreas, lung, and prostate.

CONCLUSION

NED highlighted a distinct GC entity with more suppressive TIME features correlated with tumor behaviors, indicating a cohort that would benefit more from immunotherapies.

Narrative Review of Immunotherapy in Gastroentero-Pancreatic Neuroendocrine Neoplasms

Gastroentero-pancreatic Neuroendocrine Neoplasms (GEP-NENs) are a diverse group of rare tumors that arise from neuroendocrine cells in the gastrointestinal tract and pancreas, and they can vary significantly in terms of clinical behavior and prognosis. Immunotherapy, particularly immune checkpoint inhibitors, has shown remarkable success in various malignancies by harnessing the body's immune system to target and eliminate cancer cells. Immune checkpoint inhibitor clinical studies in GEP-NENs have yielded promising outcomes, particularly in individuals with advanced and refractory disease. Objective responses and disease stabilization have been observed in some cases, even in those previously unresponsive to traditional treatments like chemotherapy or targeted therapies. However, it's important to note that the efficacy of immunotherapy in GEP-NENs can vary widely depending on tumor characteristics, the immune microenvironment, and patient factors. As such, identifying predictive biomarkers to select the most suitable patients for immunotherapy remains an ongoing challenge. Immunotherapy has considerable potential for treating GEP-NENs, but research is still in its early stages. Several combinations are being explored to enhance the effectiveness of immunotherapy and improve the outcomes of treatment, such as combining immunotherapy with other targeted therapies or chemotherapy.

Potent molecular-targeted therapies for gastro-entero-pancreatic neuroendocrine carcinoma

Neuroendocrine neoplasms (NENs), which are characterized by neuroendocrine differentiation, can arise in various organs. NENs have been divided into well-differentiated neuroendocrine tumors (NETs) and poorly differentiated neuroendocrine carcinomas (NECs) based on morphological differentiation, each of which has a distinct etiology, molecular profile, and clinicopathological features. While the majority of NECs originate in the pulmonary organs, extrapulmonary NECs occur most predominantly in the gastro-entero-pancreatic (GEP) system. Although platinum-based chemotherapy is the main therapeutic option for recurrent or metastatic GEP-NEC patients, the clinical benefits are limited and associated with a poor prognosis, indicating the clinically urgent need for effective therapeutic agents. The clinical development of molecular-targeted therapies has been hampered due to the rarity of GEP-NECs and the paucity of knowledge on their biology. In this review, we summarize the biology, current treatments, and molecular profiles of GEP-NECs based on the findings of pivotal comprehensive molecular analyses; we also highlight potent therapeutic targets for future precision medicine based on the most recent results of clinical trials.

Heterogeneous distribution pattern of CD3+ tumor-infiltrated lymphocytes (TILs) and high combined positive score (CPS) favored the prognosis of resected early stage small-cell lung cancer

PURPOSE

This study aimed to illustrate the heterogeneity of immune features in small cell lung cancer (SCLC).

METHODS

Immunohistochemistry (IHC) staining of CD3, CD4, CD8 and PD-L1 were performed with 55 SCLC FFPE samples from radical resections. Quantitative assessment of CD3+ tumor-infiltrated lymphocytes (TILs) to present the heterogeneity in the tumor and the stroma areas. Hotspots of TILs were evaluated to illustrate the potential relationship between TIL-density and its immune competence. Programmed death ligand-1 (PD-L1) expressed on both tumor TILs (t-TILs) and stroma TILs (s-TILs) was evaluated and quantitatively described as values of tumor positive score (TPS) and combined positive score (CPS). The clinical value of TPS and CPS were further identified according to their relationship with disease-free survival (DFS).

RESULTS

More abundant CD3+ TILs were observed in the tumor stroma than that within the parenchyma (15.02±2.25% vs. 1.58±0.35%) . The amount of CD3+ s-TILs were positively correlated with DFS. The CD3+/CD4+ subset of the TILs was found more favorable to DFS compared to the CD3+/CD8+ subset. Hotspots of CD3+ TILs were observed in tumor regions and patients with more Hotspots of CD3+ TILs have better outcomes. CPS were more reliable than TPS to describe PD-L1 expression in SCLC and it was found positively correlated with tumor size and DFS.

CONCLUSIONS

The immune microenvironment of SCLC was heterogeneous. Hotspots, the amount of CD3/CD4+ TILs and the CPS value were found valuable in determine the anti-tumor immunity and predicting the clinical outcome of SCLC patients.

Neuroendocrine neoplasms of the lung and gastrointestinal system: convergent biology and a path to better therapies

Neuroendocrine neoplasms (NENs) can develop in almost any organ and span a spectrum from well-differentiated and indolent neuroendocrine tumours (NETs) to poorly differentiated and highly aggressive neuroendocrine carcinomas (NECs), including small-cell lung cancer (SCLC). These neoplasms are thought to primarily derive from neuroendocrine precursor cells located throughout the body and can also arise through neuroendocrine transdifferentiation of organ-specific epithelial cell types. Hence, NENs constitute a group of tumour types that share key genomic and phenotypic characteristics irrespective of their site of origin, albeit with some organ-specific differences. The establishment of representative preclinical models for several of these disease entities together with analyses of human tumour specimens has provided important insights into crucial aspects of their biology with therapeutic implications. In this Review, we provide a comprehensive overview of the current understanding of NENs of the gastrointestinal system and lung from clinical and biological perspectives. Research on NENs has typically been siloed by the tumour site of origin, and a cross-cutting view might enable advances in one area to accelerate research in others. Therefore, we aim to emphasize that a better understanding of the commonalities and differences of NENs arising in different organs might more effectively inform clinical research to define therapeutic targets and ultimately optimize patient care.

Rectal neuroendocrine neoplasms: what the radiologists should know

Neuroendocrine neoplasms of the rectum (R-NENs) are rare; however, their incidence has increased almost threefold in the last few decades. Imaging of R-NENs includes two primary categories: anatomic/morphologic imaging comprised of endoscopic ultrasound (EUS), computed tomography (CT), magnetic resonance imaging (MRI), and functional/molecular imaging comprising of planar scintigraphy, single-photon emission computed tomography (SPECT), and positron emission tomography (PET). The management depends on stage, dimension, atypical features, histological grade, and lymphovascular invasion (LVI). Low-risk local R-NENs can be resected endoscopically, and high-risk or locally advanced neoplasms can be treated with radical surgery and lymphadenectomy and/or chemoradiation. The review article focuses on imaging illustrations and discusses applications of different imaging modalities in diagnosing and managing R-NENs.

Evaluation of PD-L1 expression in a large set of gastroenteropancreatic neuroendocrine tumours and correlation with clinicopathological data

BACKGROUND

Targeting programmed death protein 1 (PD-1) or its ligand PD-L1 is a promising therapeutic approach for many types of cancer in which PD-L1 is overexpressed. However, data on PD-L1 expression levels in gastroenteropancreatic neuroendocrine neoplasms (GEP-NENs) are limited and contradictory.

METHODS

We evaluated PD-L1 expression in 457 archived, formalin-fixed, paraffin-embedded GEP-NEN samples from 175 patients by immunohistochemistry using the highly sensitive monoclonal anti-PD-L1 antibody 73-10. The immunostaining was semiquantitatively evaluated using a 12-point immunoreactivity score (IRS) taking both PD-L1-positive tumour cells and immune cells into account. Tumour samples with an IRS ≥ 3 were considered PD-L1-positive. Results were correlated with clinicopathological data and with the expression of several typical markers and receptors for neuroendocrine tumours.

RESULTS

Of the GEP-NEN samples, 73% were PD-L1-positive. The median IRS value across all samples was 4.0, corresponding to low expression. PD-L1 immunostaining was predominantly localised at the plasma membrane of the tumour cells. Positive correlations were observed between PD-L1 expression and tumour grading or Ki-67 index, between PD-L1 expression and the expression of chromogranin A, and between PD-L1 expression and the expression of each of the five somatostatin receptors. PD-L1 expression was lower in tumours with lymph node metastases at diagnosis than in those without regional metastasis and lower in high-stage than in earlier-stage tumours. No association was noted between PD-L1 expression and patient survival.

CONCLUSIONS

PD-L1 expression is common in GEP-NENs and increases with malignancy. Therefore, especially in high-grade GEP-NENs, targeting the PD-1/PD-L1 axis could be a promising additional therapeutic strategy.

Clinical implications of immune checkpoint markers and immune infiltrates in patients with thymic neuroendocrine neoplasms

The potential response of immune checkpoint blockade (ICB) in thymic neuroendocrine neoplasms (T-NEN) is largely unknown and full of great expectations. The expression of immune checkpoint molecules and immune infiltrates greatly determine the response to ICB. However, studies regarding the immune landscape in T-NEN are scarce. This work was aimed to characterize the immune landscape and its association with clinical characteristics in T-NEN. The expression of programmed cell death protein 1 (PD-1) and its ligand, programmed death ligand-1 (PD-L1), and the density of tumor-infiltrating lymphocytes (TILs), monocytes, and granulocytes were determined by immunohistochemical (IHC) staining on tumor tissues from T-NEN. Immune landscapes were delineated and correlated with clinicopathological factors. We found that T-NEN with increased immune cell infiltration and enhanced expression of PD-1/PD-L1 tended to have restricted tumor size and less metastases. A higher density of CD8+ TILs was associated with a significantly lower rate of bone metastasis. In addition, we presented three cases of T-NEN who progressed after multiple lines of therapies and received ICB for alternative treatment. ICB elicited durable partial responses with satisfactory safety in two patients with atypical carcinoid, but showed resistance in 1 patient with large cell neuroendocrine carcinoma. This innovative study delineated for the first time the heterogeneous immune landscape in T-NEN and identified CD8+ TILs as a potential marker to predict bone metastasis. An “immune-inflamed” landscape with the presence of TILs predominated in T-NEN, making T-NEN a potentially favorable target for ICB treatment. Further judicious designs of “tailor-made” clinical trials of ICB in T-NEN are urgently needed.

Clinical implications of immune checkpoint markers and immune infiltrates in patients with thymic neuroendocrine neoplasms

The potential response of immune checkpoint blockade (ICB) in thymic neuroendocrine neoplasms (T-NEN) is largely unknown and full of great expectations. The expression of immune checkpoint molecules and immune infiltrates greatly determine the response to ICB. However, studies regarding the immune landscape in T-NEN are scarce. This work was aimed to characterize the immune landscape and its association with clinical characteristics in T-NEN. The expression of programmed cell death protein 1 (PD-1) and its ligand, programmed death ligand-1 (PD-L1), and the density of tumor-infiltrating lymphocytes (TILs), monocytes, and granulocytes were determined by immunohistochemical (IHC) staining on tumor tissues from T-NEN. Immune landscapes were delineated and correlated with clinicopathological factors. We found that T-NEN with increased immune cell infiltration and enhanced expression of PD-1/PD-L1 tended to have restricted tumor size and less metastases. A higher density of CD8+ TILs was associated with a significantly lower rate of bone metastasis. In addition, we presented three cases of T-NEN who progressed after multiple lines of therapies and received ICB for alternative treatment. ICB elicited durable partial responses with satisfactory safety in two patients with atypical carcinoid, but showed resistance in 1 patient with large cell neuroendocrine carcinoma. This innovative study delineated for the first time the heterogeneous immune landscape in T-NEN and identified CD8+ TILs as a potential marker to predict bone metastasis. An “immune-inflamed” landscape with the presence of TILs predominated in T-NEN, making T-NEN a potentially favorable target for ICB treatment. Further judicious designs of “tailor-made” clinical trials of ICB in T-NEN are urgently needed.

The Landscape and Clinical Application of the Tumor Microenvironment in Gastroenteropancreatic Neuroendocrine Neoplasms

Simple Summary

The tumor microenvironment (TME) plays a role in promoting tumor progression. Elucidating the relationship between the TME and tumor cells will benefit current therapies. Therefore, this review summarizes the most recent relationship between the TME and tumor characteristics, discusses the differences in the TME at various sites along the digestive tract, and compares the TMEs of neuroendocrine tumors and neuroendocrine carcinomas. Microbial ecological changes in the TME were reviewed. The clinical application of the TME was summarized from bench to bedside. The TME can be used as a tumor drug target for diagnostic value, prognosis prediction, and efficacy evaluation, further revealing the potential of immune checkpoints combined with antiangiogenic drugs. The clinical application prospects of adoptive cell therapy and oncolytic viruses were described. The potential therapeutic approaches and strategies for gastrointestinal neuroendocrine neoplasms are considered.

Abstract

Gastroenteropancreatic neuroendocrine neoplasms feature high heterogeneity. Neuroendocrine tumor cells are closely associated with the tumor microenvironment. Tumor-infiltrating immune cells are mutually educated by each other and by tumor cells. Immune cells have dual protumorigenic and antitumorigenic effects. The immune environment is conducive to the invasion and metastasis of the tumor; in turn, tumor cells can change the immune environment. These cells also form cytokines, immune checkpoint systems, and tertiary lymphoid structures to participate in the process of mutual adaptation. Additionally, the fibroblasts, vascular structure, and microbiota exhibit interactions with tumor cells. From bench to bedside, clinical practice related to the tumor microenvironment is also regarded as promising. Targeting immune components and angiogenic regulatory molecules has been shown to be effective. The clinical efficacy of immune checkpoint inhibitors, adoptive cell therapy, and oncolytic viruses remains to be further discussed in clinical trials. Moreover, combination therapy is feasible for advanced high-grade tumors. The regulation of the tumor microenvironment based on multiple omics results can suggest innovative therapeutic strategies to prevent tumors from succeeding in immune escape and to support antitumoral effects.

Expanding Therapeutic Opportunities for Extrapulmonary Neuroendocrine Carcinoma

Poorly differentiated neuroendocrine carcinomas (PD-NEC) are rare cancers garnering interest as they become more commonly encountered in the clinic. This is due to improved diagnostic methods and the increasingly observed phenomenon of "NE lineage plasticity," whereby nonneuroendocrine (non-NE) epithelial cancers transition to aggressive NE phenotypes after targeted treatment. Effective treatment options for patients with PD-NEC are challenging for several reasons. This includes a lack of targetable, recurrent molecular drivers, a paucity of patient-relevant preclinical models to study biology and test novel therapeutics, and the absence of validated biomarkers to guide clinical management. Although advances have been made pertaining to molecular subtyping of small cell lung cancer (SCLC), a PD-NEC of lung origin, extrapulmonary (EP)-PD-NECs remain understudied. This review will address emerging SCLC-like, same-organ non-NE cancer-like and tumor-type-agnostic biological vulnerabilities of EP-PD-NECs, with the potential for therapeutic exploitation. The hypotheses surrounding the origin of these cancers and how "NE lineage plasticity" can be leveraged for therapeutic purposes are discussed. SCLC is herein proposed as a paradigm for supporting progress toward precision medicine in EP-PD-NECs. The aim of this review is to provide a thorough portrait of the current knowledge of EP-PD-NEC biology, with a view to informing new avenues for research and future therapeutic opportunities in these cancers of unmet need.

Complete and Durable Response to Nivolumab in Recurrent Poorly Differentiated Pancreatic Neuroendocrine Carcinoma with High Tumor Mutational Burden

Poorly differentiated pancreatic neuroendocrine carcinomas (NECs) are rare and aggressive malignancies with rapid disease progression and early widespread metastasis. Given histology similarity, they are commonly treated with platinum-based chemotherapy as small cell lung cancer (SCLC). However, no standard treatment has been established for recurrent or progressive disease. We present an Asian patient with recurrent poorly differentiated pancreatic NEC after curative surgery and adjuvant chemotherapy with cisplatin and etoposide. The tumor mutational burden (TMB) was high. The patient received chemotherapy combined with maintenance immunotherapy with nivolumab and achieved promising and durable response, suggesting TMB could be a biomarker to identify NEC patients for immune checkpoint inhibitor (ICI) treatment.

Management of Large Cell Neuroendocrine Carcinoma

BACKGROUND

Large cell neuroendocrine carcinoma (LCNEC) is a rare, aggressive cancer with a dismal prognosis. The majority of cases occur in the lung and the gastrointestinal tract; however, it can occur throughout the body. Recently advances in the understanding of the molecular underpinnings of this disease have paved the way for additional novel promising therapies. This review will discuss the current best evidence for management of LCNEC and new directions in the classification and treatment of this rare disease.

METHODS

We performed a PubMed search for "Large cell neuroendocrine carcinoma" and "High grade neuroendocrine carcinoma." All titles were screened for relevance to the management of LCNEC. Papers were included based on relevance to the management of LCNEC.

RESULTS

Papers were included reviewing both pulmonary and extra pulmonary LCNEC. We summarized the data driven best practices for the management of both early and advanced stage LCNEC. We describe emerging therapies with promising potential.

DISCUSSION

LCNEC are rare and aggressive neoplasms. In advanced disease, the historical regimen of platinum based therapy in combination with etoposide or irinotecan remains among the commonly used first line therapies, however for extra thoracic LCNEC regimens like FOLFOX, FOLFOIRI and CAPTEM can also be used. Further effective and safe treatment options are desperately needed. Recently, new advances including a new understanding of the genetic subcategories of LCNEC and immunotherapy agents may guide further treatments.

Diagnosis and Management of Gastrointestinal Neuroendocrine Neoplasms

The latest WHO classification cleanly divides gastrointestinal neuroendocrine neoplasms into neuroendocrine tumor (NET; well-differentiated, any grade) and neuroendocrine carcinoma (NEC; poorly differentiated, high-grade by definition), along with mixed neuroendocrine-non-neuroendocrine neoplasms. NECs are always aggressive, with multiple mutations; they are treated with chemotherapy. NETs have widely different presentations, behavior, and management depending on site of origin. Esophageal examples are vanishingly rare. Most gastric and appendiceal tumors are indolent, as are many colonic and rectal tumors. The duodenum is home to some unusual variants of NET, and jejunal/ileal NETs frequently metastasize, which impacts their staging and clinical management.

Impacts of pembrolizumab therapy on immune phenotype in patients with high-grade neuroendocrine neoplasms

High grade neuroendocrine neoplasms (G3 NENs) are rare aggressive tumors with limited treatment options. Twenty-one previously treated patients with metastatic extra-pulmonary G3 NENs were treated with pembrolizumab. Baseline tumor samples were assessed for PD-L1 and tumor infiltrating lymphocytes (TIL). Peripheral blood samples drawn pre-treatment, prior to cycle three, and at disease progression were analyzed by flow cytometry. One patient achieved partial response, two had stable disease, and 18 exhibited progressive disease. The partially responding patient did not progress after 392 days, and the median progression-free survival (PFS) was 59 days. Longer PFS correlated independently with higher pre-treatment peripheral blood T-cell counts and lower pre-treatment activation state (CD69 expression) of naïve T cells and NK cells. Peripheral T-cell viability was reduced in patients with greater TILs. Post-treatment, T cells had reduced numbers of CD4+ cells, reduced PD-1 expression, increased activation of effector (CD62L-) cells, and increased expression of TIGIT. Baseline TIGIT expression on peripheral T cells also correlated positively with Ki67 in tumor. Patients with higher baseline T-cell expression of TIM-3 had shorter PFS. Despite limited activity of pembrolizumab, this study highlights the immune phenotype in this rare tumor type before and after treatment. High baseline peripheral T-cell count and reduced activation of T and NK cell subsets were associated with improved outcomes. Furthermore, increased post-treatment TIGIT and elevated baseline TIM-3 expression suggest that these may limit the efficacy of pembrolizumab, providing a rationale for combination immunotherapy (PD-1 with TIGIT and/or TIM-3 antibodies) to treat extra-pulmonary G3 NENs.

Immunotherapy and potential predictive biomarkers in the treatment of neuroendocrine neoplasia

Neuroendocrine neoplasias (NENs) are a heterogeneous group of rare tumors scattered throughout the body. Surgery, locoregional or ablative therapies as well as maintenance treatments are applied in well-differentiated, low-grade NENs, whereas cytotoxic chemotherapy is usually applied in high-grade neuroendocrine carcinomas. However, treatment options for patients with advanced or metastatic NENs are limited. Immunotherapy has provided new treatment approaches for many cancer types, including neuroendocrine tumors, but predictive biomarkers of immune checkpoint inhibitors (ICIs) in the treatment of NENs have not been fully reported. By reviewing the literature and international congress abstracts, we summarize the current knowledge of ICIs, potential predicative biomarkers in the treatment of NENs, implications and efficacy of ICIs as well as biomarkers for NENs of gastroenteropancreatic system, lung NENs and Merkel cell carcinoma in clinical practice.

Programmed Cell Death Ligand Expression Drives Immune Tolerogenesis across the Diverse Subtypes of Neuroendocrine Tumours

INTRODUCTION

A comprehensive characterization of the tumour microenvironment is lacking in neuroendocrine tumours (NETs), where programmed cell death-1 receptor-ligand (PD-1/PD-L1) inhibitors are undergoing efficacy testing.

OBJECTIVE

We investigated drivers of cancer-related immunosuppression across NETs of various sites and grades using multi-parameter immunohistochemistry and targeted transcriptomic profiling.

METHODS

Tissue microarrays (n = 102) were stained for PD-L1 and 2 and indoleamine deoxygenase-1 (IDO-1) and evaluated in relationship to functional characteristics of tumour-infiltrating T-lymphocytes (TILs) and biomarkers of hypoxia/angiogenesis. PD-L1 expression was tested in circulating tumour cells (CTCs, n = 12) to evaluate its relationship with metastatic dissemination.

RESULTS

PD-L1 expression was highest in lung NETs (n = 30, p = 0.007), whereas PD-L2 was highest in pancreatic NETs (n = 53, p < 0.001) with no correlation with grade or hypoxia/angiogenesis. PD-L1+ NETs (n = 26, 25%) had greater CD4+/FOXP3+ and CD8+/PD1+ TILs (p < 0.001) and necrosis (p = 0.02). CD4+/FOXP3+ infiltrate had the highest PD-L1/IDO-1 co-expressing tumours (p = 0.006). Grade 3 well-differentiated NETs had lower CD4+/FOXP3+ and CD8+/PD1+ TIL density (p < 0.001), and NanoString immune profiling revealed enrichment of macrophage-related transcripts in cases with poorer prognosis. We identified PD-L1(+) CTC subpopulations in 75% of evaluated patients (n = 12).

CONCLUSIONS

PD-L1 expression correlates with T-cell exhaustion independent of tumour hypoxia and is enhanced in a subpopulation of CTCs, suggesting its relevance to the progression of NETs. These findings support a potential therapeutic role for PD-L1 inhibitors in a subset of NETs.

Molecular profile of pancreatic neuroendocrine neoplasms (PanNENs): Opportunities for personalized therapies

Pancreatic neuroendocrine neoplasms (panNENs) are the second most common epithelial tumors of the pancreas. Despite improvements in prognostic grading and staging systems, it remains a challenge to predict the clinical behavior of panNENs and the response to specific therapies given the high degree of heterogeneity of these tumors. Most panNENs are nonfunctional and present as advanced disease. However, systemic therapies provide modest benefits. Therefore, there is a need for predictive biomarkers to develop personalized treatment and to advance new drug development. The somatostatin receptors remain the only clinically established prognostic and predictive biomarkers in panNENs. Oncogenic drivers are at a very low frequency. Commonly mutated genes in panNENs include MEN1, chromatin remodeling genes (DAXX and ATRX), and mammalian target of rapamycin pathway genes. In contrast, poorly differentiated neuroendocrine carcinomas (panNECs), which carry a very poor prognosis, have distinctive mutations in certain genes (eg, RB1 and p53). Ongoing research to integrate epigenomics will provide tremendous opportunities to improve current understanding of the clinical heterogeneity of pancreatic neuroendocrine tumors and provide invaluable insight into the biology of these tumors, new drug development, and establishing personalized therapies.

Novel immunotherapy strategies for treatment of neuroendocrine neoplasms

Neuroendocrine tumors (NETs) and neuroendocrine carcinomas (NECs) are a heterogeneous family of neoplasms. Well-differentiated tumors are often slow growing and characterized by low tumor mutational burden. Poorly differentiated NECs are aggressive, with an increased mutational burden and higher propensity to express PD-L1. While the therapeutic landscape for neuroendocrine neoplasms (NENs) has evolved substantially over the past decade, immunotherapy has been unexplored in NENs until recently. Checkpoint inhibitors such as anti-PD-1 and anti-CTLA-4 agents, bi-specific tumor-targeting antibodies, and chimeric antigen receptor (CAR) T-cell therapy are examples of treatments that have demonstrated efficacy in other cancers and have recently been investigated in NENs. This review examines the immune landscape of NENs in detail, summarizes recent clinical study results, and discusses potential future directions for immunotherapy.

Programmed cell death protein 1/programmed death ligand 1 but not HER2 is a potential therapeutic target in gastric neuroendocrine carcinoma

AIMS

Gastric neuroendocrine carcinoma (NEC) is a rare and aggressive subtype with a poor prognosis. We aim to investigate expression profiles of HER2 and programmed death ligand 1 (PD-L1) in gastric NEC to test the potential applicability of drugs targeting these molecules.

METHODS AND RESULTS

Expression levels of HER2 and PD-L1 were evaluated in 25 gastric NECs, including 10 pure NECs and 15 mixed adenocarcinoma-NECs, and a combined positive score (CPS) was used to evaluate PD-L1 expression. The correlations of expression levels with both clinicopathological features and the expression of p53, retinoblastoma protein (Rb) and mismatch repair proteins were also analysed. Eighteen of the 25 (72%) cases showed a PD-L1 CPS of ≥ 1, which was previously shown to be associated with response to pembrolizumab. Positive nodal metastasis and low tumour-infiltrating lymphocyte (TIL) levels at the invasive margin were significantly associated with a PD-L1 CPS of < 1. The NEC component was HER2-negative in all cases, whereas HER2 positivity was observed in the adenocarcinoma component of six of 15 (40%) mixed adenocarcinoma-NECs. Mismatch repair deficiency, a mutant pattern of p53 expression and loss of Rb expression were observed in four (16%), 17 (68%) and nine (36%) cases, respectively, although these alterations were not associated with the PD-L1 CPS or other clinicopathological characteristics.

CONCLUSIONS

HER2 is unlikely to be an effective target in gastric NEC owing to the lack of HER2 expression, whereas the PD-1/PD-L1 pathway is a potential therapeutic target for gastric NEC because of the relatively high prevalence of a PD-L1 CPS of ≥ 1 in this subtype.

Immune Checkpoint Markers in Neuroendocrine Carcinoma of the Digestive System

Digestive system neuroendocrine carcinomas (NECs) are rare neoplasms originating from neuroendocrine cells with a poor prognosis and limited effective treatments. Programmed cell death protein 1/ligand 1 (PD-1/PD-L1) blockade has been used in the management of more than 10 solid tumors and has achieved promising clinical outcomes. PD-L1 expression, immune cell infiltration, tumor mutational burden (TMB), and microsatellite instability (MSI) are all verified biomarkers that can predict the response to anti-PD-1/PD-L1 therapy. Here, we investigated PD-L1 expression and immune cell infiltration density by immunohistochemical (IHC) staining of tumor samples from 33 patients with digestive system NECs. Tumor and paratumor normal samples from 31 of these patients underwent whole-exome sequencing to evaluate TMB and the MSI-high (MSI-H) status. In total, 29.0% of digestive system NECs had positive PD-L1 expression according to the tumor proportion score (TPS). Infiltration of CD3+, CD8+, and CD68+ cells was observed in 69.7, 27.3, and 54.5% of patients, respectively. The TMB value for patients sequenced ranged from 0.57 to 11.75 mutations/Mb, with a median of 5.68 mutations/Mb. mSINGS, MSIsensor, and MSIseq were used to analyze the MSI status according to the sequencing data, and in our evaluation, no MSI-H status was detected. Our data might indicate a limited potential of anti-PD-1/PD-L1 monotherapy in digestive system NECs, although clinical trials are warranted.

Gastroenteropancreatic High-Grade Neuroendocrine Neoplasms: Histology and Molecular Analysis, Two Sides of the Same Coin

BACKGROUND

In gastroenteropancreatic (GEP) high-grade neuroendocrine neoplasms (H-NENs), Ki-67 threshold of 55% defines three prognosis subclasses: neuroendocrine tumor (NET) G3, neuroendocrine carcinoma (NEC) <55%, and NEC ≥55%. We investigated whether the molecular profiling of H-NENs differs among these subcategories and evaluated potential therapeutic targets, including PD-L1.

METHODS

In GEP-NEN patients, we evaluated: (i) 55% threshold for Ki-67 labeling index for further stratifying NEC and (ii) immunoreactivity and gene mutations by immunohistochemistry and targeted next-generation sequencing (T-NGS).

RESULTS

Fifteen NETs G3 and 39 NECs were identified. Ki-67 labeling index was <55% in 9 NECs and ≥55% in 30 NECs. Gene mutations by NGS (TP53, 32.9%; KRAS, 5.5%; BRAF, 4.1%) were detected in 46.6% NENs, significantly enriched in NEC ≥55% (76.7%) compared to NEC <55% (55.6%) or NET (20.0%). PD-L1 staining in tumor-infiltrating lymphocytes was observed in NEC ≥55% (36.7%; p = 0.03). Median OS was 4.3 years in NET G3, 1.8 years in NEC <55%, and 0.7 years in NEC ≥55% (p <0.0001); it was 2.3 years with NGS wild-type, 0.7 years with ≥1 mutation (p <0.0001), 0.8 years in PD-L1-positive patients, and 1.7 years in PD-L1-negative subjects (p = 0.0004). In multivariate analysis, only the proposed subclassification approach yielded statistically significant differences between groups (NEC <55% vs. NET G3, HR 14.1, 95% CI 2.2-89.8, p = 0.005; NEC ≥55% vs. NET G3, HR 25.8, 95% CI 3.9-169, p = 0.0007).

CONCLUSIONS

These findings identify NEC ≥55% as a biologically and prognostically distinct subtype and pave the way for more personalized treatment.

Gastroenteropancreatic neuroendocrine neoplasms and inflammation: A complex cross-talk with relevant clinical implications

Neuroendocrine neoplasms (NENs) are a group of tumors originating from the neuroendocrine system. They mainly occur in the digestive system and the respiratory tract. It is well-know a strict interaction between neuroendocrine system and inflammation, which can play an important role in NEN carcinogenesis. Inflammatory mediators, which are produced by the tumor microenvironment, can favor cancer induction and progression, and can promote immune editing. On the other hand, a balanced immune system represents a relevant step in cancer prevention through the elimination of dysplastic and cancer cells. Therefore, an inflammatory response may be both pro- and anti-tumorigenic. In this review, we provide an overview concerning the complex interplay between inflammation and gastroenteropancreatic NENs, focusing on the tumorigenesis and clinical implications in these tumors.

PD-L1 Expression Patterns in Microsatellite Instability-High Intestinal Adenocarcinoma Subtypes

OBJECTIVES

To investigate patterns of programmed death protein-1 (PD-L1) expression in microsatellite instability (MSI)-high intestinal carcinomas and correlate them with pathologic and molecular features.

METHODS

One hundred and fifteen MSI-high and 41 microsatellite stable carcinomas were included. Tumor sections were immunohistochemically labeled for PD-L1. The results were correlated with histologic subtypes, MSI, and BRAF status.

RESULTS

As expected, MSI status was associated with PD-L1 expression. Among 115 MSI-high tumors, PD-L1 expression was observed on tumor cells in 28 tumors and on tumor-associated inflammatory cells in 77 tumors. Medullary carcinoma demonstrated more frequent PD-L1 expression on tumor cells than mucinous and typical adenocarcinoma. PD-L1 expression was more frequent in medullary and typical adenocarcinoma than in mucinous adenocarcinoma based on combined positive scores. Tumors with more nucleotide shifts by PCR-based MSI testing were more likely to express PD-L1.

CONCLUSIONS

Expression of PD-L1 is different among different histologic subtypes of MSI-high intestinal carcinomas.

PD-L1 Expression and Immune Cell Infiltration in Gastroenteropancreatic (GEP) and Non-GEP Neuroendocrine Neoplasms With High Proliferative Activity

The potential of neuroendocrine neoplasms (NEN) to respond to checkpoint inhibitors is largely unknown and full of great expectations. Immunohistochemical (IHC) studies of programmed cell death ligand 1 (PD-L1) expression in the tumor microenvironment and its implications in predicting the response to checkpoint inhibition is a very active subject. Currently, the combined analysis of PD-L1 expression and tumor-associated immune cell (TAIC) infiltration is considered the best predictive marker of therapeutic response. Here we investigated the expression of PD-L1 on tumor cells (TC) and tumor-infiltrating immune cells (IC) by IHC in 68 NEN samples with a high proliferation rate (Ki-67 >20%) from 57 patients and in 22 samples we correlated it with TAIC density by assessing intratumoral infiltration of CD3+, CD8+, and CD68+ cells. Furthermore, the tumor microenvironment was evaluated according to the classification of Teng et al. We detected PD-L1 expression in 31.6% of NEN G3. Its expression usually was weak and more IC than TC expressed PD-L1. The proportion of tumors positive for PD-L1 was comparable in NEN from different sites of origin but varied depending on tumor differentiation and disease extension. No positive IHC staining was found in 3 well-differentiated neuroendocrine tumors (NETs) with a proliferation rate above 20% (NET G3). When analyzing TAIC, we rarely (18.2%) detected intratumoral CD8+ cells, whereas infiltration by CD3+ and CD68+ cells was more common (45.5 and 59.1%, respectively). By combining CD3+ cells and PD-L1 status, we identified the immune ignorant phenotype of tumor microenvironment as being the most common phenotype, supporting the concept of a preferably combined immunotherapeutic approach in neuroendocrine carcinoma (NEC).

Neuroendocrine neoplasms: current and potential diagnostic, predictive and prognostic markers

Some biomarkers for functioning and non-functioning neuroendocrine neoplasms (NENs) are currently available. Despite their application in clinical practice, results should be interpreted cautiously. Considering the variable sensitivity and specificity of these parameters, there is an unmet need for novel biomarkers to improve diagnosis and predict patient outcome. Nowadays, several new biomarkers are being evaluated and may become future tools for the management of NENs. These biomarkers include (1) peptides and growth factors; (2) DNA and RNA markers based on genomics analysis, for example, the so-called NET test, which has been developed for analyzing gene transcripts in circulating blood; (3) circulating tumor/endothelial/progenitor cells or cell-free tumor DNA, which represent minimally invasive methods that would provide additional information for monitoring treatment response and (4) improved imaging techniques with novel radiolabeled somatostatin analogs or peptides. Below we summarize some future directions in the development of novel diagnostic and predictive/prognostic biomarkers in NENs. This review is focused on circulating and selected tissue markers.

Immune checkpoint markers in gastroenteropancreatic neuroendocrine neoplasia

Cancer immunotherapy has evolved major breakthroughs in the last years. The cell-surface receptor programmed death-1 (PD-1) and its ligand, programmed death ligand-1 (PD-L1), have been detected in various cancer types. However, the analysis on gastroenteropancreatic neoplasia (GEP-NENs) is limited. Therefore, the aim of this study was to characterize GEP-NENs with regard to PD-1/PD-L1 pathway and tumor-infiltrating lymphocytes (TILs). On protein level, we examined TILs, PD-1 and PD-L1 expression in tumor tissue of 244 GEP-NENs using immunohistochemistry. Expression levels were correlated with clinicopathological parameters including long-term survival in an observational study. In total, 244 patients could be included. Most of the patients had a NEN of the small intestine (52.5%) or the pancreas (29.5%). All tumors could be graded by their morphology and Ki67 index, with 57.8% G1, 34% G2 and 8.2% G3 tumors. High TILs (19.6%) and high PD-1 (16.1%) expression showed a significant correlation with shorter patient survival (P < 0.05) and with a higher grading. Furthermore, expression of PD-L1 (8.7%) showed a trend to shorter patient survival. High TILs and PD-1 expression are significantly associated with shorter patient survival and higher grading in GEP-NENs. PD-L1 expression showed a trend to shorter patient survival. Immunotherapy might be a promising therapeutic approach in GEP-NENs especially in tumors with high TILs.

Molecular Diagnostics in the Neoplasms of Small Intestine and Appendix: 2018 Update

Neoplasms of the small intestine are rare in comparison with colorectal tumors. The most common tumor types arising in the small intestine are adenocarcinomas, well-differentiated neuroendocrine tumors, gastrointestinal stromal tumors, and lymphoma. Primary appendiceal neoplasms are rare and found in less than 2% of appendectomy specimens with an incidence of approximately 1.2 cases per 100,000 people per year in the United States. This article explores molecular diagnostics in the neoplasms of small intestine and appendix.

Analysis of the immune landscape of small bowel neuroendocrine tumors

Immune checkpoint inhibitors have shown promising results in different cancers, and correlation between immune infiltration, expression of programmed death-ligand 1 (PD-L1) by tumor cells and response to immunotherapy has been reported. There is limited knowledge regarding the immune microenvironment of small bowel (SB) neuroendocrine tumors (NETs). This work was aimed at characterizing the immune landscape of SB NETs. Expression of PD-L1 and programmed death-1 (PD-1) was evaluated by immunohistochemistry in 102 surgically resected, primary NETs of the duodenum, jejunum and ileum. Extent and characteristics of the tumor-associated immune infiltrate were also assessed and investigated in their prognostic potential. We detected the expression of PD-L1 in ≥1 and ≥50% of tumor cells in 40/102 (39%; 95% CI, 30-49%) and 14/102 (14%; 95% CI, 8-22%) cases respectively. Intratumor host immune response was apparently absent in 35/102 cases (34%; 95% CI, 25-44%), mild to moderate in 46/102 samples (45%, 95% CI, 35-55%), intense in 21/102 tumors (21%, 95% CI, 13-30%). Expression of PD-L1 and extent of immune infiltration were significantly higher in duodenal NETs as compared with jejunal/ileal NETs. A marked peritumoral host response was organized as ectopic lymph node-like structures in 18/102 cases (18%; 95% CI, 11-26%). Neither PD-L1 expression nor the degree of immune infiltration showed any prognostic significance. Overall, the immune landscape of SB NETs is heterogeneous, with adaptive immune resistance mechanisms prevailing in duodenal NETs. Clinical trials of immune checkpoint inhibitors should take into account the immune heterogeneity of SB NETs.

The Tumor Microenvironment in Neuroendocrine Tumors: Biology and Therapeutic Implications

Neuroendocrine tumors (NETs) include a heterogeneous group of malignancies arising in the diffuse neuroendocrine system and characterized by indolent growth. Complex interactions take place among the cellular components of the microenvironment of these tumors, and the recognition of the molecular mediators of their interplay and cross talk is crucial to discover novel therapeutic targets. NET cells overexpress a plethora of proangiogenic molecules including vascular endothelial growth factor, platelet-derived growth factor, fibroblast growth factor, semaphorins, and angiopoietins that promote both recruitment and proliferation of endothelial cell precursors, thus resulting among the most vascularized cancers with a microvessel density 10-fold higher than epithelial tumors. Also, NETs operate multifaceted interactions with stromal cells, both at local and distant sites, and whether their paracrine secretion of serotonin, connective tissue growth factor, and transforming growth factor β primarily drives the fibroblast activation to enhance the tumor proliferation, on the other side NET-derived profibrotic factors accelerate the extracellular matrix remodeling and contribute to heart valves and/or mesenteric fibrosis development, namely, major complications of functioning NETs. However, at present, little is known on the immune landscape of NETs, but accumulating evidence shows that tumor-infiltrating neutrophils, mast cells, and/or macrophages concur to promote the neoangiogenic switch of these tumors by either direct or indirect mechanisms. On the other hand, immune checkpoint molecules are heterogeneously expressed in NETs' surrounding cells, and it is unclear whether or not tumor-infiltrating lymphocytes are antitumor armed within the microenvironment, given their low mutational load. Here, we review the current knowledge on both gastroenteropancreatic and pulmonary NETs' microenvironment as well as both established and innovative treatments aimed at targeting the tumor-host interplay.

Neuroendocrine Differentiation, Microsatellite Instability, and Tumor-infiltrating Lymphocytes in Advanced Colorectal Cancer With BRAF Mutation

BACKGROUND

Approximately 10% of metastatic colorectal cancer (mCRC) cases will harbor the BRAF p.V600E mutation (BRAF-mCRC) and have been associated with a poor prognosis. Although they are usually considered a unique clinical entity, biologic heterogeneity has been described. We performed an extensive clinicopathologic study of a multicenter series of BRAF-mCRC to highlight differences between tumors with microsatellite instability (MSI) and microsatellite stable tumors, focusing on both inflammatory profiles and neuroendocrine differentiation.

METHODS

We included 59 BRAF-mCRC cases and collected the clinical data (ie, surgery, treatment, and follow-up). We evaluated MSI status, budding, lympho-angioinvasion, neuroinvasion, extent of active stroma, CD3⁺ and CD8⁺ intratumoral and peritumoral lymphocytes, programmed cell death ligand 1, p53, Ki-67, synaptophysin, and CDX2 expression.

RESULTS

The 22 MSI BRAF-mCRC cases were associated with the right side (P < .0001), an expansive grown pattern (P < .01), programmed cell death ligand 1 expression (P < .0001), high CD8 T-cell content (P = .0001), and lymph node metastases (P < .029). The 37 MSS BRAF-mCRC cases were characterized by a greater stromal component (P = .0002), pulmonary metastases (P = .095), and p53 and synaptophysin immunoreactivity (P = .004 and P = .001, respectively). Univariate analysis demonstrated that MSI and a high CD8 T-cell content were associated with a 34% (hazard ratio [HR], 0.66; 95% confidence interval [CI], 0.34-1.28; P = .2) and 33% (HR, 0.67; 95% CI, 0.45-0.99; P = .04) reduction in the risk of death, respectively. The combined presence of MSI and CD8 T-cell content decreased the hazard of mortality ≤ 63% (HR, 0.37; 95% CI, 0.14-0.97; P = .2), which was slightly reduced after multivariate analysis.

CONCLUSION

A simultaneous evaluation of MSI, CD8 T-cell content, and neuroendocrine markers could allow for the identification of subsets of BRAF-mCRC with a different prognosis and potential eligibility for specific treatments.

Neuroendocrine neoplasms of rectum: A management update

The estimated annual incidence of R-NENs is 1.04 per 100,000 persons although the real incidence may be underestimated, as not all R-NEN are systematically reported in registers. Also the prevalence has increased substantially, reflecting the rising incidence and indolent nature of R-NENs, showing the highest prevalence increase among all site of origin of NENs. The size of the tumor reveals the behavior of R-NENs where the risk for metastatic spread increases for lesions > 10 mm. Applying the WHO 2010 grading system to whole NENs originating in the gastroenteropancreatic system, R-NENs are classified as Well-Differentiated Neuroendocrine Tumors (WD-NET), which contain NET G1 and NET G2, and Poorly-Differentiated Carcinomas (PD-NEC) enclosing only G3 neoplasms for which the term carcinoma is applied. The treatment is endoscopic resection in most cases: conventional polypectomy or endoscopic mucosal resection (EMR) for smaller lesions or endoscopic submucosal resection with a ligation device (ESMR-L), cap-assisted EMR (EMR-C) and endoscopic submucosal dissection (ESD). However it is important to know when the endoscopic treatment is not enough, and surgical treatment is indicated, or when the latter could be unnecessary. For PD-NECs, it has recently been demonstrated that chemoradiotherapy is associated with a similar long-term survival to that obtained with surgery. As well, new targeted-agents chemotherapy may be indicated for metastatic WD-NETs.