Expression of delta-like protein 3 is reproducibly present in a subset of small cell lung carcinomas and pulmonary carcinoid tumors

Highlights

• Interobserver agreement for DLL3 expression is substantial among thoracic pathologists.

• High DLL3 expression (≥ 50% of tumor cells) is observed in almost 80% of small cell lung carcinomas.

• Approximately one third of atypical and typical carcinoid tumors show high DLL3 expression.

• High DLL3 expression is associated with better overall survival in small cell lung carcinomas.

Abstract

Objectives

Delta-like protein 3 (DLL3), an inhibitory Notch ligand, is the target for rovalpituzumab tesirine in development for the treatment of small cell lung cancer (SCLC). We studied the expression of DLL3, its reproducibility and prognostic role in pulmonary neuroendocrine tumors.

Materials and Methods

Institutional pathology files were searched for resected pulmonary neuroendocrine tumors (1995–2017). Expression of DLL3 (clone SP347) was categorized as high (≥50% of tumor cells) or low (<50%). Interobserver agreement among 5 thoracic pathologists was measured by Krippendorff’s α coefficient. Staging (N = 148) was performed according to the 8th AJCC.

Results

Our study included 157 patients with a median age of 62.2 years (range 23.2–88.1) including 59 men (37.6%). Tumors included 44 (28.0%) SCLC, 46 (29.3%) atypical and 67 (42.7%) typical carcinoid tumors at stages I (N = 83, 56.1%), II (N = 28, 18.9%), and III/IV (N = 37, 25.0%). Interobserver agreement for high vs low DLL3 expression (N = 70) was 82.9% (α = 0.79, substantial). High DLL3 expression was observed in 35 (79.5%) SCLC, 17 (37.0%) atypical and 22 (32.8%) typical carcinoid tumors. High DLL3 was associated with SCLC morphology (p < 0.0001). During a median follow-up of 4.2 years (range, 2 days–20.3 years), 70 patients died; 19 died from disease. High DLL3 expression was associated with better overall survival in SCLC (p = 0.049) but not after adjusting for age, tumor size and stage.

Conclusions

DLL3 expression is reliably quantifiable by pathologists and is highly expressed in the majority of SCLC and a subset of carcinoid tumors, making it an attractive target for anti-DLL3 treatment.

Introduction

Pulmonary neuroendocrine tumors represent a spectrum of neoplasms ranging from low and intermediate grade lesions such as typical and atypical carcinoid tumors, respectively to high grade malignancies including small cell lung carcinomas (SCLC) and large cell neuroendocrine carcinomas (LCNEC). The outcome of these tumors differs with reported 5-years survival of 79 to 99% for typical carcinoid tumors [[1], [2], [3]] to only 1 to 2% for extensive stage SCLC [4,5].

Whereas there has been successful development of many targeted therapies for adenocarcinomas of the lung and immunotherapies for adenocarcinomas, squamous cell carcinomas and small cell carcinomas, there has been very little development beyond targeting somatostatin receptors for pulmonary neuroendocrine tumors. These somatostatin receptors are often lacking in high grade neuroendocrine tumors. Therefore, more effective targeted therapies are sought to specifically treat patients with high grade pulmonary neuroendocrine carcinomas, but also patients with carcinoid tumors who are not curable with surgery alone. In addition, while morphology and stage are important prognostic parameters, other predictive factors are sought for individualized treatment and management of these patients.

The Notch pathway has been implicated in the oncogenesis of SCLC [6]. Specifically, Notch signaling has been found to suppress tumor growth in neuroendocrine tumors [6,7]. Delta-like protein 3 (DLL3), a member of the Notch family, has been identified as an inhibitory ligand of the Notch signaling pathway [8]. Initial studies suggested that DLL3 is highly upregulated and aberrantly expressed on the cell surface of SCLC. If confirmed, DLL3 could represent a potential therapeutic target in that disease, as an antibody-drug conjugate with high specificity for DLL3, rovalpituzumab tesirine (Rova-T), has been recently identified [9]. In vivo studies have shown that Rova-T induces durable tumor regression in multiple patient-derived xenograft tumor models of SCLC with a strong correlation between level of DLL3 expression and therapeutic activity [9]. A subsequent phase I clinical trial including patients with SCLC and LCNEC confirmed encouraging anti-tumor activity in 11 of 60 (18%) patients who received active doses of Rova-T having an objective response [10]. Ten of 26 (35%) patients with available tissue that showed high DLL3 expression (50% or more of tumor cells expressing DLL3) had a confirmed objective response in contrast to 8 of 8 (100%) patients with low DLL3 expression who did not show an objective response. Similarly, Rova-T treatment prevented tumor growth for over 100 days in a patient derived small cell bladder cancer xenograft animal model [11]. Furthermore, DLL3-expressing IDH mutant tumorsphere lines were shown to be susceptible to Rova-T in contrast to IDH wildtype DLL3-negative cell lines [12].

Other DLL3-targeting agents are in development, including a bispecific anti-DLL3/CD3 antibody (AMG 757, NCT03319940) and chimeric antigen receptor T cells targeting DLL3 (AMG 119, NCT03392064). Collectively, these reports support a potential role for anti-DLL3 treatment of highly aggressive tumors, specifically small cell carcinomas, when the drug is combined with a DNA-damaging toxin. These findings support the importance of testing of DLL3 expression in these tumors and implicate DLL3 as a predictive biomarker for the therapy for high grade pulmonary neuroendocrine carcinomas. However, the rate of expression and potential prognostic role of DLL3 in pulmonary neuroendocrine tumors needs to be studied more thoroughly. In addition, interobserver reproducibility of DLL3 expression has not been investigated.

We studied the expression of DLL3 in pulmonary neuroendocrine tumors and investigated the reproducibility of DLL3 expression among multiple thoracic pathologists. We also explored clinical features that might be associated with DLL3 expression and the prognostic role of this marker in pulmonary neuroendocrine tumors.