Gene Expression Profiling of Phenotypically-Defined Hormone-Receptor Positive Breast Cancer: Evidence for Increased Transcriptional Activity of the Insulin Growth Factor Receptor Pathway and Other Pathways.

Abstract Background: Approximately 70% of all breast cancers are hormone receptor (HR)-positive tumors that are sensitive to endocrine therapy, but some patients have recurrence despite adjuvant endocrine therapy. We performed an exploratory analysis of gene expression in HR-pos operable breast cancer in order to identify potential novel therapeutic targets and biomarkers associated with recurrence. Methods: RNA was extracted from primary tumor samples obtained from 776 patients with stage I-III breast cancer treated with adjuvant chemohormonal therapy in trial E2197 (JCO 2008; 26: 4092-4099), of whom 458 had HR-pos disease (defined in a central lab; JCO 2008; 26: 2473). We evaluated RNA expression patterns (by quantitative RT-PCR using a panel of 371 rationally selected genes) in HR-pos cases compared with the HR-neg cases using weighted T statistics, and determined which genes in the HR-pos, HER2-neg group were associated with recurrence (using Cox proportional hazards model score test, Korn's adjusted P value <5% with false discovery rate < 10%).Results: The top 10 genes exhibiting significantly higher expression in the HR-pos group (p≤ 6.17e-160) included ESR1 plus 5 estrogen regulated genes, confirming our approach of evaluating gene expression in phenotypically-defined subsets. Other pathways that exhibited higher expression in the HR-pos group (among the 40 top genes with higher expression, p<8.66e-53) included the insulin growth factor (IGF) (IRS1, IGFR1, IGFB2), Ras (RhoB, RhoC, RAB27B, GGPS1), and HER pathways (ERBB2, ERBB3, ERBB4), and other genes involved in apoptosis (BCL2, BCL2L1, BAG1, NME6, BBC3), signaling (MAPK3, SEMA3F, RXRA), mismatch repair (MSH3), cell cycle regulation (CCND1), stress response (HSPB1), and tumor suppressor genes (TP53BP1, APC). These patterns were similar in HER2-pos cases. Pathway analysis (Ingenuity) revealed substantial interconnectivity among these genes, especially between IGFR1, ERB2/3/4, MAPK3, BCL2, and CCND1, but not RhoB/RhoC. Genes for which increased expression was associated with increased recurrence included those associated with proliferation (TOP2A, AURKB, PLK1) and apoptosis (BIRC5 - survivin).Conclusions: This exploratory analysis reveals several pathways that exhibit higher transcriptional expression in HR-pos disease, some of which are also associated with a higher risk of recurrence, suggesting that they may be potential therapeutic targets. This provides rationale for testing agents currently available in the clinic that inhibit the IGF and other pathways. Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 5165.