Abstract P5-13-01: Transcript analysis of PI3K and immune-related genes and gene signatures in the pre- and post-treatment samples from the window of opportunity study of anastrozole and anastrozole with pictilisib (GDC-0941) in patients with HR-positive early breast cancer (OPPORTUNE study)
Authors: Schmid P , Pinder SE , Bundred N , Wheatley D , Macaskill J , Zammit C , Hu J , Price R , Shia A , Lim L , Parker P , Molinero L , Yu J , O'Brien C , Wilson T , Savage H , Derynck M , Lackner MR , Amler L , Purushotham A , Thompson A , Gendreau S 
Published: May 2016

Background: The OPPORTUNE Study randomized postmenopausal patients (pts) to receive 2-week preoperative treatment with anastrozole (ANA) plus pictilisib ("ANA+PIC" arm) or ANA alone. Patients had newly diagnosed, operable, ER+, HER2- invasive breast cancer of ≥1 cm size. The primary outcome at interim analysis (n=70) revealed that the addition of PIC significantly increased the anti-proliferative response to ANA as measured by reduction in Ki67 immunohistochemistry (IHC). Multivariate analyses suggested benefit of PIC for patients with luminal B disease (Schmid et al. SABCS 2014).

Methods: RNA expression analysis of ∼800 breast cancer-related genes was performed on patients analyzed at the interim analysis, including 14 (ANA) and 20 (ANA+PIC) patients with matched pre- and post- treatment paired tumour samples using the nCounter platform (NanoString). Differential expression of individual genes by arm was assessed using paired and moderated t-tests and statistical significance assessed through false discovery rate (FDR). Ingenuity Pathway Analysis (IPA) of differentially expressed transcripts identified pathways of relevance. Protein expression was analyzed by reverse protein array ( RPPA) in pre- and post-treatment samples.

Results: In an unsupervised analysis, down-regulation of genes associated with ER signaling was observed in patients who received single-agent ANA and ANA+PIC, which included genes that regulate the cell cycle, cell death, survival, growth and proliferation and known ER target genes (e.g., PGR, GREB1). In addition, transcripts related to growth factor signaling pathway appeared to be specifically modulated in the ANA+PIC arm, possibly via the upregulation of the expression of RTK ligands. There were no clear changes in PI3K-related phosphoproteins (e.g., AKT, S6, 4E-BP1) in the post-treatment samples by RPPA. However, known PI3K-regulated genes, IRS2 and PIK3IP1, were upregulated in the post-treatment samples and a composite PI3K gene expression signature score (O'Brien et al. 2010) was reduced in both study arms following treatment. This PI3K signature was associated with pre-treatment luminal B status (n=27) and, consistent with this finding, the baseline PI3K gene signature score in the ANA arm, but not the ANA+PIC arm, was inversely associated with the decrease in post treatment Ki67. The tumor immune microenvironment was analyzed though the use of composite gene sets. In our initial observations, analysis of pre- and post-treatment samples showed that 2-week treatment with ANA resulted in a modest increase in transcripts associated with multiple immune signatures, which was further enhanced by the addition of PIC.

Conclusions: Gene expression analysis of pre- and post-treatment samples in the OPPORTUNE study demonstrates on-target inhibition of ER and PI3K signaling networks. The analysis of additional paired samples is in progress to further assess if 2-weeks of treatment with a regimen containing an AI in patients with early breast cancer impacts the tumor immune microenvironment.

Citation Format: Schmid P, Pinder SE, Bundred N, Wheatley D, Macaskill J, Zammit C, Hu J, Price R, Shia A, Lim L, Parker P, Molinero L, Yu J, O'Brien C, Wilson T, Savage H, Derynck M, Lackner MR, Amler L, Purushotham A, Thompson A, Gendreau S. Transcript analysis of PI3K and immune-related genes and gene signatures in the pre- and post-treatment samples from the window of opportunity study of anastrozole and anastrozole with pictilisib (GDC-0941) in patients with HR-positive early breast cancer (OPPORTUNE study). [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P5-13-01.