Abstract 5251: ASCL1 and RET expression define a clinically relevant subgroup of lung adenocarcinoma characterized by neuroendocrine differentiation

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA ASCL1 is an important regulatory transcription factor in pulmonary neuroendocrine cell development, but its value as a biomarker of neuroendocrine differentiation in lung adenocarcinoma (AD) and as a potential prognostic biomarker remains unclear. We examined ASCL1expression in lung cancer samples of varied histologic subtype, clinical outcome, and smoking status and compared to expression of traditional neuroendocrine markers. ASCL1 mRNA expression was found almost exclusively in smokers with AD, in contrast to non-smokers. ASCL1 protein expression by immunohistochemistry (IHC) correlated best with synaptophysin compared to chromogranin and CD56/NCAM. Analysis of a compendium of 367 microarray-based gene expression profiles in stage I lung adenocarcinomas identified significantly higher expression levels of the RET oncogene in ASCL1 positive tumors (ASCL1+) compared to ASCL1- tumors (q-value < 10 - 9). High levels of RET expression in ASCL1+ but not in ASCL1- tumors was associated with significantly shorter overall survival in stage 1 (p = 0.007) and in all AD (p = 0.037). RET protein expression by IHC had an association with overall survival in the context of ASCL1 expression. In silico gene set analysis and in vitro experiments by ASCL1 shRNA in AD cells with high endogenous expression of ASCL1 and RET implicated ASCL1 as a potential upstream regulator of the RET oncogene. Also, silencing ASCL1 in AD cells markedly reduced cell growth and motility. These results suggest that ASCL1 and RET expression define a clinically relevant subgroup of approximately 10% of AD characterized by neuroendocrine differentiation. Citation Format: Farhad Kosari, Cristiane M. Ida, Marie Christine Aubry, Lin Yang, Irina V. Kovtun, Janet L. Schaefer Klein, Sandra C. Tomaszek, Stephen J. Murphy, Ping Yang, Dennis Wigle, George Vasmatzis. ASCL1 and RET expression define a clinically relevant subgroup of lung adenocarcinoma characterized by neuroendocrine differentiation. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5251. doi:10.1158/1538-7445.AM2014-5251