Abstract P5-13-05: Gene expression changes with neoadjuvant hormonal treatment

Breast cancers (BC) expressing estrogen and/or progesterone receptors, referred to as hormone receptor (HR)-positive represent the largest molecular subset of breast tumors. Fortunately, estrogen receptor expression on the cell surface serves as a drug target for endocrine therapy. In HR+, human epidermal growth factor receptor-2 (HER2) negative BC, neoadjuvant endocrine therapy (NET) is being increasingly used. While NET has been shown to reduce tumor cell proliferation causing apoptosis, up to 20% of tumors do not respond. Currently there are no validated predictive gene signatures distinguishing responders from non-responders to NET. Furthermore, there are limited data on the effects of different NET regimens in vivo and how they vary between responders and non-responders. Methods: We conducted a retrospective translational study in patients who were treated with NET at our institution. This study was approved by our institutional review board. Paired pre-treatment and surgical samples were collected from 24 patients along with clinico-pathological information. Responders were defined as those with a preoperative endocrine prognostic index (PEPI) score of 0. RNA isolation was performed using the Roche HighPure FFPET RNA Isolation spin-column kit. Purified RNA was hybridized with the PanCancer Code Set and finally the cartridge was scanned on the nCounter Digital Analyzer. Raw counts from each gene were imported into the nSolver Analysis. Log2 normalized data obtained from Nanostring nCounter analysis was analyzed for differentially expressed genes between pre- and post-treatment samples. The bioinformatics analysis was carried out using nCounter analysis software. Results: The median age at diagnosis was 64 years and NET used was anastrozole alone or in combination with fulvestrant. At baseline the majority of tumors were invasive ductal carcinomas (n=18), grade II (n=18), with a Ki67% >15% (n=16). Median duration of treatment with NET was 5 months (range 2-10 months). Nine tumors were defined as responders to NET and 15 were non-responders. In all of the 24 paired samples, we found 123 genes with a statistically significant change in expression (defined by greater than two-fold change and a false discovery rate adjusted p-value Conclusions: In our retrospective translational study we found that NET upregulates genes in the Jak-STAT, MAPK, RAS, cytosine-cytosine receptor interaction and PI3K-Akt signaling pathways and downregulates cell cycle pathway genes independent of type or duration of NET. We also found multiple genes involving the PI3K-Akt and Notch pathway were differentially expressed in pre-treatment specimens among responders compared to non-responders. While the sample size comparing responders versus non-responders was inadequate, our results suggest some early trends which warrant further investigation. Citation Format: Darien E Reed, Ritu Pandey, Jennifer M Segar, Michele Chu, Lauren LeBeau, Pavani Chalasani. Gene expression changes with neoadjuvant hormonal treatment [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P5-13-05.