4247 - Changes in ER pathway activity score during neoadjuvant letrozole to assess therapy response and predict disease free survival (DFS) in ER positive breast cancer patients

Background

Despite ER positive IHC staining, some patients do not respond to neoadjuvant endocrine therapy, suggesting that ER staining lacks specificity to predict response. We developed a method to infer a quantitative signal transduction pathway activity score (PAS) from mRNA levels (microarray, qPCR) of pathway-associated transcription factor target genes. Initial studies suggest that ER PAS may have higher specificity than ER IHC in predicting endocrine therapy response. In this study, we correlated pre-treatment ER PAS and changes in ER PAS during neoadjuvant letrozole treatment to therapy response and DFS.

Methods

We collected fresh frozen RNA from tumor samples of 30 ER IHC positive post-menopausal patients with primary localized breast cancer, treated with neoadjuvant letrozole at Edinburgh Western General. In total, 30 pre, 25 mid (median 27 days), and 29 post-treatment (median 136 days) samples were analysed. Clinical outcome was assessed (RECIST, n = 29) at circa 3 months treatment by 3D ultrasound, with 1 complete (CR), 21 partial responses (PR), 2 stable (SD), and 5 progressive diseases (PD). Using RT-qPCR, target gene expression was measured for ER, androgen receptor, PI3K, Hedgehog, TGFβ and Wnt pathways. PAS were expressed on a normalized scale (0 to 100).

Results

Pre-treatment ER PAS was significantly higher in responders (CR/PR) than non-responders (SD/PD), PAS=45 vs 24, respectively, T-test p = 0.01. Pre-treatment ER PAS correlated with decrease in ER PAS during treatment (cor=0.87 and 0.7, mid and-post treatment, respectively). At mid-treatment, ER PAS of responders had decreased to PAS of non-responders (20 vs 19, respectively), remaining low during further treatment. Decrease in ER PAS was significantly higher in responders (-30) than non-responders (-6), p = 0.01. Higher ER PAS after treatment correlated to shorter DFS (COX proportional hazards p = 0.02). Baseline PAS of other pathways did not correlate with response, but changed significantly during treatment.

Conclusions

This study confirms that ER PAS in ER-positive patients, measured before and after neoadjuvant endocrine therapy, has potential to predict and assess therapy response, and predict DFS.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

Philips Electronics Nederland B.V., acting through its HealthWorks Molecular Pathway Dx.

Funding

Has not received any funding.

Disclosure

M. A. Inda: Full / Part-time employment: Philips Reseach. A. van de Stolpe: Full / Part-time employment, has Philips stocks: Philips Research. D. Keizer: Full / Part-time employment: Philips. D. Clout: Full / Part-time employment: Philips Reasearch. H. van Zon: Full / Part-time employment: Philips Reasearch. M. Akse: Full / Part-time employment: Philips. All other authors have declared no conflicts of interest.