Abstract 1468: Circulating tumor cells (CTCs) and circulating tumor microemboli (CTM) from patients with small cell lung cancer (SCLC) show heterogeneity in epithelial to mesenchymal transition (EMT) phenotype and evidence of vasculogenic mimicry (VM).

Background: Circulating tumour cells (CTCs) and circulating tumour microemboli (CTM) are prevalent in patients with aggressive small cell lung cancer (SCLC). Heterogeneity in epithelial and mesenchymal phenotypes in CTCs and within CTM was investigated given evidence in preclinical models of epithelial and mesenchymal cell co-operativity advantageous for hematogenous spread and the role of epithelial to mesenchymal transition (EMT) in invasion and metastasis. Methods: Four colour immunofluorescence assays were developed and applied to tumour cells enriched by filtration from peripheral blood of extensive stage SCLC patients prior to treatment. CTCs/CTM were assessed for expression of cytokeratins (CKs, epithelial marker) and vimentin (mesenchymal marker) with DAPI stained nuclei and negative selection of leukocytes and circulating endothelial cells (CECs) by CD45 and/or vascular endothelial-cadherin (VE-cadherin, CD144) expression respectively. Results and Conclusions: CTCs were identified in all patients that expressed epithelial and/or mesenchymal markers. Individual CTM were detected comprised of tumour cells of heterogeneous EMT status and CTM were also observed containing leukocytes and/or CECs. There was substantial heterogeneity in CK and vimentin expression in CTCs and within CTM consistent with EMT plasticity and with co-operativity between epithelial and mesenchymal tumour cells. A subpopulation of CTCs co-expressed CKs and VE-cadherin that intriguingly, raises the possibility that vascular mimicry accompanies and may facilitate hematogenous spread in this aggressive tumor type. Further studies are required to explore this new hypothesis. Citation Format: Robert Metcalf, Jessica Booth, Rajeeb Swain, Steven Bagley, Karen Morris, Matthew Krebs, Andrew Hughes, Gerard Brady, Fiona Blackhall, Caroline Dive. Circulating tumor cells (CTCs) and circulating tumor microemboli (CTM) from patients with small cell lung cancer (SCLC) show heterogeneity in epithelial to mesenchymal transition (EMT) phenotype and evidence of vasculogenic mimicry (VM). [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1468. doi:10.1158/1538-7445.AM2013-1468