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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.

Purpose: We have previously developed the caspase-based radiotracer, 18 F-ICMT-11, for PET imaging to monitor treatment response. We further validated 18 F-ICMT-11 specificity in a murine melanoma death-switch tumour model with conditional activation of caspase-3 induced by doxycycline. Methods: Caspase-3/7 activity and cellular uptake of 18 F-ICMT-11, 18 F-ML-10 and 18 F-FDG were assessed in B16ova and B16ovaRevC3 cells after death-switch induction. Death-switch induction was confirmed in vivo in xenograft tumours, and 18 F-ICMT-11 and 18 F-ML-10 biodistribution was assessed by ex vivo gamma counting of select tissues. PET imaging was performed with 18 F-ICMT-11, 18 F-ML-10 and 18 F-FDG. Caspase-3 activation was confirmed by immunohistochemistry. Results: Significantly increased caspase-3/7 activity was observed only in B16ovaRevC3 cells after death-switch induction, accompanied by significantly increased 18 F-ICMT-11 (p < 0.001) and 18 F-ML-10 (p < 0.05) and decreased 18 F-FDG (p < 0.001) uptake compared with controls. B16ova and B16ovaRevC3 tumours had similar growth in vivo; however, B16ovaRevC3 growth was significantly reduced with death-switch induction (p < 0.01). Biodistribution studies showed significantly increased 18 F-ICMT-11 tumour uptake following death-switch induction (p < 0.01), but not for 18 F-ML-10. Tumour uptake of 18 F-ICMT-11 was higher than that of 18 F-ML-10 after death-switch induction. PET imaging studies showed that 18 F-ICMT-11 can be used to detect apoptosis after death-switch induction, which was accompanied by significantly increased expression of cleaved caspase-3. 18 F-FDG signal decreased in tumours after death-switch induction. Conclusions: We demonstrate that 18 F-ICMT-11 can be used to detect caspase-3 activation in a death-switch tumour model, independent of the confounding effects of cancer therapeutics, thus confirming its specificity and supporting the development of this radiotracer for clinical use to monitor tumour apoptosis and therapy response.