Abstract A32: Colorectal cancer stroma: Tumor cells in disguise

Abstract Background: Epithelial-to-mesenchymal transition (EMT) is thought to mediate cancer cell dissemination and metastasis. However, the role of EMT in the initial progression of human cancer remains unproven, since delaminating neoplastic cells have never been identified in the peritumoral stroma. Aim: To demonstrate the existence of EMT-neoplastic cells in mesenchymal disguise in the stroma of human colorectal cancer (CRC). Methods and Materials / Patients: In vitro, gene expression profile analysis of 18 CRC cells by microarray. Transfection/silencing of TWIST1 in CRC cells and invasion and migration assay. Immunohistochemistry for TWIST1 of 11 adenomas and of 201 CRC specimens. Combined TWIST1 immunofluorescence and in situ hybridization (iFISH) for CEP7 and 20 of 20 CRC specimens. In vivo, orthotopic graft of murine CRC cells CT26 in the rectal sub-mucosa of Balb/c mice. Results: TWIST1 was necessary to maintain mesenchymal phenotype and invasiveness of microsatellite-stable (MSS) cellular models of EMT, either spontaneous (CoLo741) or induced by transfection (SW480). TWIST1 mRNA was not translated in MSI CRC cells (HCT116). In an orthotopic mouse model of CRC, syngenic TWIST1-positive cells (CT26) acquired a mesenchymal phenotype when invading the peritumoral tissues. In human CRC tissues, the presence of TWIST1-positive cells within the stroma correlated with tumor MSS status (p=0.05), stage IV (p=0.02), and patient prognosis (DSS, p<0.01). Trisomies of chromosome 7 and/or chromosome 20 were detected within the tumor compartment of 17/20 CRC specimens. In each of these 17 tumors, TWIST1-positive cells with matching chromosomal gains were traceable in the peritumoral stroma (86 of 776 counted cells, 11.1%), whereas no trisomy was recognized in TWIST1-negative stromal cells (0 of 1249 cells; p<0.001). Conclusion: TWIST1 plays a crucial role in maintaining EMT in human CRC. By using TWIST1 as marker of EMT cells, we demonstrated that stromal cells, disguised as fibroblasts, are actually neoplastic. Targeting TWIST1+ stromal cells might open new scenarios for interfering with the metastatic cascade of CRC. Note: This abstract was not presented at the conference. Citation Format: Giuseppe Celesti, Giuseppe Di Caro, Paolo Bianchi, Fabio Grizzi, Gianluca Basso, Andrea Doni, Federica Marchesi, Giancarlo Marra, Massimo Roncalli, Alberto Mantovani, Alberto Malesci, Luigi Laghi. Colorectal cancer stroma: Tumor cells in disguise. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Invasion and Metastasis; Jan 20-23, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;73(3 Suppl):Abstract nr A32.