RNAseq Analysis of the Sorafenib Phase III DECISION Trial in Differentiated Thyroid Cancer (DTC): Correlation with Clinical Outcome.

6083 Background: In DECISION, sorafenib significantly impacted progression-free survival (PFS) and response rate (RR) in radioactive-iodine refractory DTC. The aim of this biomarker study was to identify RNA expression profiles related with PFS, overall survival (OS) and RR and to describe the expression profiles of DTC histologies. Methods: Of the 417 patients in the trial, 247 had sufficient formalin fixed paraffin embedded archival tumor material for RNAseq. We generated on average 77 million paired-end reads for each sample on HiSeq2000 (Illumina). RNAseq reads were mapped against the human reference genome (GRCh38) with STAR (v2.5.1b) using ENCODE parameters. 125 samples had sufficient quality to be included in the analysis. Results: The analysis subset included 68 sorafenib and 57 placebo patients (PFS 10.3 vs 7.4 months, HR: 0.62 CI 95% 0.38-0.99, p = 0.046). Unsupervised clustering using the 100 most variable genes identified 3 groups: BRAF-like (included most of the BRAF-mutated tumors), RAS-like (included most of the RAS mutated tumors) and non-BRAF-non-RAS-like group (included most wild-type tumors). These groups, based on the mutational profile, can be correlated with tumor type: the papillary BRAF-mutant, the follicular wild-type, and a third group with papillary, follicular and poorly differentiated with predominant RAS mutations. A Student t-test comparing papillary and follicular histologies revealed a signature of 283 genes with significantly different expression that, within the papillary tumors, identifies a subset with an expression profile more similar to follicular. No RNA signatures correlating with benefit from sorafenib were identified. Conclusions: While papillary and follicular thyroid cancers have significantly different RNA expression profiles, a subset of papillary has been identified with an expression profile more similar to follicular. In addition, a unified RAS-like expression profile spans subsets of papillary, follicular, and poorly differentiated thyroid cancers, suggesting that tumor biology can be similar across histologies. Clinical trial information: NCT00984282.