Abstract 5295: Impact of a multi-gene expression profile in predicting adjuvant trastuzumab outcome in HER2-positive breast cancer
Authors: Sara Ravaioli, Roberta Maltoni, Francesca Pirini, Michela Palleschi, William Balzi, Elisabetta Petracci, Giovanni Martinelli, Andrea Rocca, Sara Bravaccini
Journal: Cancer Research (2020)

Abstract Background Trastuzumab is the cornerstone of adjuvant therapy for HER2-positive breast cancer (BC), but up to 20% of patients relapse. Understanding resistance mechanisms could allow developing strategies to overcome this issue. We performed a case-control, retrospective study to compare the gene expression profiles (GEPs) of 27 patients who experienced disease relapse within 2 years from the start of adjuvant trastuzumab therapy, with those of 27 patients who were disease-free after at least 5 years. Here, we present the preliminary results on 12 cases and 12 controls, matched by age and hormone receptor status. Methods RNA was isolated from formalin-fixed paraffin-embedded primary tumors (FFPE) with AllPrep DNA/RNA FFPE Kit (Qiagen) and quantified by Nanodrop, before performing Nanostring gene expression profile. nCounter Breast Cancer 360 Panel (Nanostring Technologies) was used according to manufacturer's instructions. nSolver analysis software (Nanostring Technologies) was used to obtain normalized counts and to compare GEPs between cases and controls, considering as significant a Benjamini Yekutieli (BY) corrected p-value ≤0.05. Mann-Whitney median test was used to compare Ki67 score and Body Mass Index (BMI) between cases and controls. Results Out of 770 analyzed genes, none was significantly differentially expressed at BY p-value &amp;lt;0.05, probably due to the low number of cases. Five genes were differentially expressed with a BY p-value &amp;lt;0.1: CDKN1A (Log2 fold change -0.733, 95% CI: -1.06 − -0.409), GDF15 (Log2 fold change -1.92, 95% CI: -2.78 − -1.05), TFDP1 (Log2 fold change -0.567, 95% CI: -0.826 − -0.309) and ELF3 (Log2 fold change -1.52, 95%CI: -2.22 − -0.813) were downregulated in control patients, whereas TNFSF10 (Log2 fold change 1.27, 95% CI: 0.669 − 1.88) was upregulated. CDKN1A and TFDP1 are cell cycle regulators: the former encodes for p21, which inhibits cell cycle progression and is involved in DNA damage repair; the latter encodes a transcription factors that dimerizes with E2F, promoting cell cycle genes' transcription. GDF15 codes for a secreted ligand of the TGF-beta superfamily and acts as a pleiotropic cytokine involved in response to hypoxia, inflammation, acute injury and oxidative stress. ELF3 is a transcriptional activator involved in vascular inflammation and a critical downstream effector of HER2 pathway. TNFSF10 encodes a cytokine belonging to the TNF ligand family, inducing apoptosis in tumor cells. No differences were found between cases and controls considering Ki67 proliferation index and BMI. Conclusions Our preliminary results indicate that altered expression of genes involved in cell cycle, apoptosis, inflammation and stress response are involved in trastuzumab resistance. The validation of these results overall series is ongoing. The relations between GEPs and clinico-pathological features will be assessed. Citation Format: Sara Ravaioli, Roberta Maltoni, Francesca Pirini, Michela Palleschi, William Balzi, Elisabetta Petracci, Giovanni Martinelli, Andrea Rocca, Sara Bravaccini. Impact of a multi-gene expression profile in predicting adjuvant trastuzumab outcome in HER2-positive breast cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5295.