Evaluation of gene expression by RNA-seq after single dose of trastuzumab (T) reveals predictors of pathologic complete response (pCR) in HER2-positive early breast cancer.

Abstract

10558 Background: The use of a ‘brief exposure’ to single agent T allows the measurement of dynamic changes in the transcriptome that may predict response to T-based combinations. We have shown that most gene expression changes in HER2+ tumors treated with T occur in tumors that ultimately achieve a pCR. Our further analysis suggests several patterns of transcriptional change in pCR tumors suggesting different mechanisms of action of T. RNA-seq analysis provides more in-depth annotation of these mechanisms. Methods: Fresh tumor core biopsies were taken at a 2 week time point after a single dose of T (8mg/m2) from 80 HER2+ early breast cancer patients enrolled on a clinical trial of T>T+C. Nucleic acids were extracted using Qiagen AllPrep and were analyzed with Illumina HT12v3 Beadchip and Illumina 610 QUAD V1 SNP arrays. RNA was also processed for sequencing using the Ovation RNA-Seq System and paired-end sequenced using an Illumina Genome Analyzer IIxRNA-seq data was analyzed with Tophat/Cufflinks. Network analysis was performed with Metacore. Results: Among pCR tumors, distinct patterns of differential expression pre/post T were observed, in both microarray and RNA-seq data. ERBB2 down-regulation was characteristic of pCR in one subgroup by microarray. In this group, differentially expressed genes belonged to interaction networks involved in apoptosis and cell cycle regulation. In contrast, tumors with no change in ErbB2 showed differentially expressed genes that belonged to networks related to chromatin assembly and regulation of immune pathways. NOLC1, RPL41, ZCHHC17, and B2M had altered alternative splicing product distributions in both groups. In the ERBB2 down-regulated group, genes with changed expression were enriched for targets of STAT3 and YY1. Conclusions: RNA-seq and microarray reveal distinct responses in tumors that achieve pCR to T-containing regimens. These methods provide predictive markers for validation in subsequent clinical trials.