Controversial issues and new discoveries in lung neuroendocrine tumors

Head-to-head: Should Ki67 proliferation index be included in the formal classification of pulmonary neuroendocrine neoplasms?

The reporting of lung neuroendocrine neoplasms (NENs) according to the 2021 World Health Organisation (WHO) is based on mitotic count per 2 mm2, necrosis assessment and a constellation of cytological and immunohistochemical details. Accordingly, typical carcinoid and atypical carcinoid are low- to intermediate-grade neuroendocrine tumours (NETs), while large-cell neuroendocrine carcinoma (NEC) and small-cell lung carcinoma are high-grade NECs. In small-sized diagnostic material (cytology and biopsy), the noncommittal term of carcinoid tumour/NET not otherwise specified (NOS) and metastatic carcinoid NOS have been introduced with regard to primary and metastatic diagnostic settings, respectively. Ki-67 antigen, a well-known marker of cell proliferation, has been included in the WHO classification as a non-essential but desirable criterion, especially to distinguish NETs from high-grade NECs and to delineate the provisional category of carcinoid tumours/NETs with elevated mitotic counts (> 10 mitoses per mm2) and/or Ki-67 proliferation index (≥ 30%). However, a wider use of this marker in the spectrum of lung NENs continues to be highly reported and debated, thus witnessing a never-subsided attention. Therefore, the arguments for and against incorporating Ki-67 in the classification and clinical practice of these neoplasms are discussed herein in detail.

Clinical implications of lung neuroendocrine neoplasm classification

INTRODUCTION

Neuroendocrine neoplasms of the lung (Lung NENs) encompass NE tumors (NETs), which are in turn split into typical and atypical carcinoids, and NE carcinomas (NECs), which group together small-cell carcinoma and large-cell NE carcinoma. This classification is the current basis for orienting the daily practice of these patients, with diagnostic, prognostic, and predictive inferences.

AREAS COVERED

The clinical implications of lung NEN classification are addressed according to three converging perspectives, which were dissected through an extensive literature overview: (1) how to put intratumor heterogeneity into the context of the current classification; (2) how to contextualize immunohistochemistry markers to improve diagnosis, prognosis, and therapy prediction; and (3) how to use immuno-oncology strategies for life-threatening NECs, which still account for 90% or more of lung NENs.

EXPERT OPINION

We provide practical insights to account for intratumor heterogeneity, practice the choice of immunohistochemistry markers, and emphasize once again the added value of immuno-oncology in the setting of personalized medicine of lung NENs.

Recent advances in the molecular landscape of lung neuroendocrine tumors

INTRODUCTION

Neuroendocrine tumors of the lung (Lung-NETs) make up a heterogenous family of neoplasms showing neuroendocrine differentiation and encompass carcinoids and neuroendocrine carcinomas. On molecular grounds, they considered two completely distinct and separate tumor groups with no overlap of molecular alterations nor common developmental mechanisms. Areas covered: Two perspectives were evaluated based on an extensive review and rethinking of literature: (1) the current classification as an instrument to obtaining clinical and molecular insights into the context of Lung-NETs; and (2) an alternative and innovative interpretation of these tumors, proposing a tripartite separation into early aggressive primary high-grade neuroendocrine tumors (HGNET), differentiating or secondary HGNET, and indolent NET. Expert opinion: We herein provide an alternative outlook on Lung-NETs, which is a paradigm shift to current pathogenesis models and expands the understanding of these tumors.

The Role of Systemic Therapy in the Management of Stage I Large Cell Neuroendocrine Carcinoma of the Lung

INTRODUCTION

The optimal treatment strategy for resected stage I large cell neuroendocrine carcinoma of the lung (LCNEC) remains unknown. In this analysis, we evaluate the impact of systemic chemotherapy on patients with stage I LCNEC who have undergone surgical resection.

METHODS

The study population included patients who underwent surgical resection for LCNEC and had pathologic stage I disease. We compared overall survival between patients who underwent surgical resection alone and those who underwent surgical resection plus chemotherapy. Overall survival was estimated by the Kaplan-Meier method, and comparisons were analyzed by using multivariable Cox models and propensity score-matched analyses.

RESULTS

From 2004 to 2013, 1232 patients underwent surgical resection for stage I LCNEC in the National Cancer Database, including 957 patients (77.7%) who underwent surgical resection alone and 275 (22.3%) who received both surgery and systemic chemotherapy. Five-year survival was significantly improved in patients who received chemotherapy (64.5% versus 48.4% [hazard ratio =0.54, 95% confidence interval: 0.43-0.68, p < 0.001]). Multivariable Cox modeling confirmed the survival benefit from chemotherapy for patients with resected stage I LCNEC (hazard ratio = 0.54, 95% confidence interval: 0.43-0.68, p <0.0001). The survival benefit was further confirmed by propensity-matched analysis. In addition, older (age >70 years), comorbid white patients who underwent sublobar resections for tumors larger than 20 mm had worse survival outcomes.

CONCLUSION

In this largest-reported retrospective study of patients with resected stage I LCNEC, survival was improved in patients who received chemotherapy in both stage IA and stage IB LCNEC.

Ki-67 labeling index of neuroendocrine tumors of the lung has a high level of correspondence between biopsy samples and surgical specimens when strict counting guidelines are applied

Optimal histopathological analysis of biopsies from metastases of neuroendocrine tumor (NET) of the lung requires more than morphology only. Additional parameters such as Ki-67 labeling index are required for adequate diagnosis, but few studies have compared reproducibility of different counting protocols and modalities of reporting on biopsies of lung NET. We compared the results of four different manual counting techniques to establish Ki-67 LI. On 47 paired biopsies and surgical specimens from 22 typical carcinoids (TCs), 14 atypical carcinoids (ACs), six large cell neuroendocrine carcinomas (LCNECs), and five small cell carcinomas (SCCs) immunohistochemical staining of Ki-67 antigen was performed. We counted, in regions of highest nuclear staining (HSR), a full ×40-high-power field (diameter = 0.55 mm), 500 or 2000 cells, or 2 mm² surface area, including the HSR or the entire biopsy fragment(s). Mitoses and necrosis were evaluated in an area of 2 mm² or the entire biopsy fragment(s). Between the four counting methods, no differences in Ki-67 LI were observed. However, a Ki-67 LI higher than 5% was found in only four cases when in an HSR, 500 cells were counted (18%), five (23%) when in an HSR 2000 cells were counted, four (18%) when 2 mm² were counted, and one (5%) TC case when the entire biopsy was counted. A 20% cutoff distinguished TC and AC from LCNEC and SCC with 100% specificity and sensitivity, while mitoses and necrosis failed to a large extent. Ki-67 LI in biopsy samples was concordant with that in resection specimens when 2000 cells, 2 mm², or the entire biopsy fragment(s) were counted. Our results are important for clinical management of patients with metastases of a lung NET.

Next-Generation Sequencing of Pulmonary Large Cell Neuroendocrine Carcinoma Reveals Small Cell Carcinoma-like and Non-Small Cell Carcinoma-like Subsets

PURPOSE

Pulmonary large cell neuroendocrine carcinoma (LCNEC) is a highly aggressive neoplasm, whose biologic relationship to small cell lung carcinoma (SCLC) versus non-SCLC (NSCLC) remains unclear, contributing to uncertainty regarding optimal clinical management. To clarify these relationships, we analyzed genomic alterations in LCNEC compared with other major lung carcinoma types.

EXPERIMENTAL DESIGN

LCNEC (n = 45) tumor/normal pairs underwent targeted next-generation sequencing of 241 cancer genes by Memorial Sloan Kettering-Integrated Mutation Profiling of Actionable Cancer Targets (MSK-IMPACT) platform and comprehensive histologic, immunohistochemical, and clinical analysis. Genomic data were compared with MSK-IMPACT analysis of other lung carcinoma histologies (n = 242).

RESULTS

Commonly altered genes in LCNEC included TP53 (78%), RB1 (38%), STK11 (33%), KEAP1 (31%), and KRAS (22%). Genomic profiles segregated LCNEC into 2 major and 1 minor subsets: SCLC-like (n = 18), characterized by TP53+RB1 co-mutation/loss and other SCLC-type alterations, including MYCL amplification; NSCLC-like (n = 25), characterized by the lack of coaltered TP53+RB1 and nearly universal occurrence of NSCLC-type mutations (STK11, KRAS, and KEAP1); and carcinoid-like (n = 2), characterized by MEN1 mutations and low mutation burden. SCLC-like and NSCLC-like subsets revealed several clinicopathologic differences, including higher proliferative activity in SCLC-like tumors (P < 0.0001) and exclusive adenocarcinoma-type differentiation marker expression in NSCLC-like tumors (P = 0.005). While exhibiting predominant similarity with lung adenocarcinoma, NSCLC-like LCNEC harbored several distinctive genomic alterations, including more frequent mutations in NOTCH family genes (28%), implicated as key regulators of neuroendocrine differentiation.

CONCLUSIONS

LCNEC is a biologically heterogeneous group of tumors, comprising distinct subsets with genomic signatures of SCLC, NSCLC (predominantly adenocarcinoma), and rarely, highly proliferative carcinoids. Recognition of these subsets may inform the classification and management of LCNEC patients. Clin Cancer Res; 22(14); 3618-29. ©2016 AACR.

What clinicians are asking pathologists when dealing with lung neuroendocrine neoplasms?

Lung neuroendocrine tumors (NET) are currently classified in resection specimens according to four histological categories, namely typical carcinoid (TC), atypical carcinoid (AC), large-cell neuroendocrine carcinoma (LCNEC) and small cell carcinoma (SCC). Diagnostic criteria have remained unchanged in the 2015 WHO classification, which has ratified the wide acceptance and popularity of such terminology in the pathologists׳ and clinicians׳ community. A unifying umbrella of NE morphology and differentiation has been recognized in lung NET, which has pushed to enter an unique box of invasive tumors along with diffuse idiopathic pulmonary NE cell hyperplasia (DIPNECH) as a pre-invasive lesion with a potential toward the development of carcinoids. However, uncertainties remain in the terminology of lung NET upon small samples, where Ki-67 antigen could play some role to avoid misdiagnosing carcinoids as high-grade NE tumors. Epidemiologic, clinical and genetic traits support a biological three-tier over a pathology four-tier model, according to which TC are low malignancy tumors, AC intermediate malignancy tumors and LCNEC/SCC high malignancy tumors with no significant differences in survival among them. Inconsistencies in diagnostic reproducibility, troubles in the therapy of AC and LCNEC, and limitations to histology within the same tumor category argue in favor of a global re-thinking of lung NET where a grading system could play a role. This review outlines three main key questions in the field of lung NET: (A) unbiased diagnoses, (B) the role of Ki-67 and tumor grading, and (C) management of predictive markers. Answers are still inconclusive, thus additional research is required to improve our understanding on lung NET.