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Small cell lung cancer (SCLC) is characterized by morphologic, epigenetic and transcriptomic heterogeneity. Subtypes based upon predominant transcription factor expression have been defined that, in mouse models and cell lines, exhibit potential differential therapeutic vulnerabilities, with epigenetically distinct SCLC subtypes also described. The clinical relevance of these subtypes is unclear, due in part to challenges in obtaining tumor biopsies for reliable profiling. Here we describe a robust workflow for genome-wide DNA methylation profiling applied to both patient-derived models and to patients’ circulating cell-free DNA (cfDNA). Tumor-specific methylation patterns were readily detected in cfDNA samples from patients with SCLC and were correlated with survival outcomes. cfDNA methylation also discriminated between the transcription factor SCLC subtypes, a precedent for a liquid biopsy cfDNA-methylation approach to molecularly subtype SCLC. Our data reveal the potential clinical utility of cfDNA methylation profiling as a universally applicable liquid biopsy approach for the sensitive detection, monitoring and molecular subtyping of patients with SCLC.

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.

NeuroEndocrine Carcinomas (NECs) are rare yet lethal diseases; they are frequently metastatic and have limited treatment options. Whilst progress has been made in understanding the biology of Small Cell Lung Cancer (SCLC), the most studied NEC, research on NECs from other anatomical sites lags behind. In SCLC, circulating tumor cells (CTCs) can be used to generate patient-relevant mouse models; termed CTC-Derived eXplants (CDX) which are faithful in biology and chemotherapy response to donor patients1,2. A pilot prospective study is on-going to assess the potential utility of cell-free DNA (cfDNA) and/or CellSearch (CS) CTCs (EpCAM/cytokeratin positive) as liquid biopsies and feasibility of CDX generation from patients with advanced stage extrapulmonary NECs undergoing palliative chemotherapy. CS CTCs are enumerated before and during treatment and marker-independent RosetteSep-enriched CTCs from parallel blood samples are implanted in immunodeficient mice to attempt CDX generation. Twenty-seven patients were recruited from Jun-19 to Nov-21. CS-CTCs were present in 19/27; 70% pre-treatment samples (mean 57, median 2, range 0-685 CTCs per 7.5mL of blood). CDX generation was successful from a pre-treatment CTC sample from a patient originally diagnosed with a NEC of unknown origin who responded to Platinum/Etoposide. Whole-exome sequencing of this CDX and matched pre-treatment cfDNA from the donor revealed largely overlapping copy number changes and common mutations including an activating PIK3CA mutation. In addition, there was no evidence of TP53 or RB1 loss (hallmarks of SCLC) in neither the CDX nor the donor’s cfDNA. Immunohistochemical (IHC) analysis of this CDX showed a small cell NEC morphology, 90% Ki-67 positive cells, expression of EpCAM, pan-cytokeratins and neuroendocrine (NE) diagnostic markers, concordant with the donor’s biopsy. Further IHC and RNA sequencing revealed expression of the NE transcription factor atonal homolog 1 (ATOH1)2, CK20 and abundant Merkel cell polyomavirus (MCPyV) transcripts. These characteristics prompted reclassification of the original patient diagnosis as Merkel cell carcinoma (MCC). There was only 1 CS-CTC in the parallel pre-treatment blood sample implying that EpCAM-negative CTCs may have given rise to the CDX. The CDX showed in vivo sensitivity to Platinum/Etoposide, mirroring treatment response of the donor. Ex vivo cultures from CDX-derived cells grow as suspension clusters similar to ‘classic’ SCLC and MCPyV-positive MCC cell lines. In summary, this first Merkel Cell Carcinoma CDX recapitulates the biology of the donor’s tumor. As the donor remains alive 25 months from diagnosis of advanced disease, their CDX can serve as an avatar to guide future treatment. 1. Hodgkinson et al., Nature Med 2014, 20: p. 897-903. 2. Simpson et al., Nature Cancer 2020, 1: p. 437-451. Citation Format: Melissa Frizziero, Elaine Kilgour, Kathryn L. Simpson, Dominic Rothwell, Kristopher Frese, Melanie Galvin, Yitao Chen, Alastair Kerr, Sam Humphrey, Mukarram Hossain, Juan W. Valle, Mairéad G. McNamara, Caroline Dive. The first circulating tumor cell-derived explant (CDX) model of a Merkel cell carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3098.