Abstract 3519: TGF-β pathway alteration in pancreatic neuroendocrine tumors: characterization of a novel SMAD3 translocation

Abstract

Abstract Pancreatic neuroendocrine tumors (PanNETs) are the second most common malignancy of the pancreas, and the only curative option is represented by surgery. PanNETs can be classified as well- or poorly- differentiated, based on histology. Poorly-differentiated neuroendocrine carcinomas (NECs) represent less than 10% of cases, but they are highly malignant and associated with poor prognosis, and, most importantly, the inconsistency in their clinical management is due to the insufficient data on NEC genetic features. In order to widen our knowledge of PanNET genetic alterations, we performed RNASeq analysis (using Illumina NextSeq platform) of a group of 18 PanNETs and 2 NECs. TopHat-Fusion algorithm identified, among others, a fusion involving SMAD3 transcription factor and CCDC149; the alteration of SMAD3 in a poorly differentiated NEC was particularly interesting since SMAD3 is involved in TGF-b signaling, which has an oncogenic role in malignant cells. The SMAD3-CCDC149 fusion was confirmed in the index case by RT-PCR using primers spanning the breakpoint, followed by Sanger sequencing. The fusion was also detected by FISH analysis performed on both FFPE and frozen samples. By both FISH analysis and Sanger sequencing we identified two other poorly-differentiated NEC samples characterized by the presence of the SMAD3-CCDC149 translocation. Immunohistochemical (IHC) staining revealed that the 3 tumors, positive for the SMAD3-CCDC149 fusion, were characterized by nuclear localization of SMAD3. In order to test the hypothesis that the fusion generates an active form of SMAD3 that localizes exclusively within the nucleus, we transfected BON-1 cell line with plasmids containing either SMAD3 full length or SMAD3 truncated form (the latter mimics the fusion product) showing that only the truncated form of SMAD3 had an exclusively nuclear localization. Interestingly, FISH analysis performed on 3 well-differentiated PanNET samples did not detected the presence of the SMAD3-CDC149 translocation and IHC analysis showed cytoplasmic localization of SMAD3. Moreover, IHC analysis performed on a cohort of 40 cases of non-pancreatic neuroendocrine tumors (NETs) revealed that only poor-differentiated tumors showed a significant percentage of samples with nuclear localization of SMAD3. These data support the hypothesis that the translocation is a typical phenomenon of poorly-differentiated tumors and suggests that it could be involved also in non-pancreatic NETs. In this study we identified a previous unknown SMAD3 translocation in poor-differentiated NECs, which generates an active SMAD3 form. Deepening the knowledge of the fusion product will shed light on PanNET genetic alterations, opening the way to new therapeutic strategies. Citation Format: Emanuela Brunetto, Greta Grassini, Valeria De Pascali, Anna Talarico, Francesca Invernizzi, Michaela Bowden, Massimo Loda, Luca Albarello, Massimo Falconi, Lorenza Pecciarini, Maria G. Cangi, Claudio Doglioni. TGF-β pathway alteration in pancreatic neuroendocrine tumors: characterization of a novel SMAD3 translocation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3519. doi:10.1158/1538-7445.AM2017-3519