Abstract P1-08-30: Validation of the AAGAB gene as a novel on-treatment biomarker predicting pCR in patients receiving NACT for early breast cancer
Authors: Semple Fiona , Ironside Alastair , Bownes Richard , Martinez-Perez Carlos , Wilson Natalie , Turnbull Arran , Oikonomidou Olga 
Published: March 2022

Background: Neoadjuvant chemotherapy (NACT) for breast cancer is given prior to surgery, aiming to reduce tumour burden and provide early information on response to treatment. Tumours with a pathological complete response (pCR) following NACT are less likely to recur than those in patients with residual disease following NACT, suggesting that pCR following NACT may be a surrogate of good prognosis. In addition, NACT provides a “window of opportunity” where sequential sampling of a tumour enables observation of changes occurring in response to treatment. We previously demonstrated that on-treatment biomarkers improve the accuracy of predicting response before resection, by performing differential gene expression analysis across sequential samples from 50 patients, across 3 time points; pre NACT, mid chemo and post NACT (Bownes et al, 2019). A single gene marker (AAGAB) was identified as a novel potential on-treatment biomarker for pCR, with greater predictive accuracy than currently established prognostic tests, supporting the potential value of on-treatment biomarker monitoring in breast cancer to improve the accuracy of tumour response prediction. Aim: To validate and test the finding that increased expression of AAGAB at mid-chemotherapy associates with pCR in ER+ve and HER+ve breast cancer patients receiving NACT. Method: mRNA extracted from tumour from the mid-chemotherapy time point during NACT, from 28 breast cancer patients, was analysed using real-time reverse transcription-PCR (real-time RT-PCR). Firstly, mRNA was reverse transcribed using Invitrogen SuperScript IV Reverse Transcriptase (RT), then cDNA was used in an Applied Biosystems real-time RT-PCR Taqman Gene Expression Assay to measure AAGAB gene expression. GAPDH and SYMPK Taqman assays were used as endogenous controls, to allow calculation of (ΔΔCt) using the Comparative CT Method. Quantitative PCR was carried out on the Applied Biosystems StepOnePlusTM Real-Time PCR System and Relative Quantitation (RQ) was calculated using 2^-(ΔΔCt). For each patient RCB (residual cancer burden) was plotted against AAGAB expression and statistical significance calculated using the Wilcoxon rank sum exact test. Results: As a group, patients with RCB scores of 0 and I demonstrated a significantly higher level of expression that patients with RCB II and RCB III. We also observed that patients with pCR after NACT demonstrated higher levels of AAGAB expression. This increased expression was also seen in patients with a decrease in tumour cellularity of more than 85%. Conclusion: Our data suggest that measurement of AAGAB expression may provide an informative on-treatment biomarker of response to NACT.

Citation Format: Fiona Semple, Alastair Ironside, Richard Bownes, Carlos Martinez-Perez, Natalie Wilson, Arran Turnbull, Olga Oikonomidou. Validation of the AAGAB gene as a novel on-treatment biomarker predicting pCR in patients receiving NACT for early breast cancer [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P1-08-30.