Abstract 4353: Utilizing scRNA sequencing to understand biomarkers of response and resistance to Sacitizumab Govetican in localized TNBC

Abstract Triple-Negative Breast Cancer (TNBC) is an aggressive breast cancer subset, which lacks expression of estrogen receptors, progesterone receptors, and human epidermal growth factor receptor-2. This subset of breast cancer disproportionately affects Black and African American women and improving TNBC treatment options is vital to reducing breast cancer mortality. The novel antibody-drug conjugate, Sacitizumab Govetican (SG), which targets TROP2 at the cell surface, has shown promising clinical results from the NeoSTAR trial (NCT04230109), a phase II study evaluating neoadjuvant SG therapy in a localized TNBC setting. As part of the NeoSTAR clinical trial, we have collected and processed pre- and post- SG treatment patient samples, with the aim of understanding response to this monotherapy. Herein, we identify biomarkers of response and resistance to SG monotherapy through the use of single cell RNA sequencing of matched pre- and post-treatment patient biopsies combined with exome sequencing these patient samples. Pre-treatment core needle biopsy samples, and if applicable, post-treatment residual disease biopsies were dissociated into single cell suspensions and subjected to single cell RNA sequencing. Additionally, fixed patient tissue samples were processed accordingly for exome sequencing analyses. Overall, we analyzed over 144,000 cells from 37 total scRNA seq libraries with an average of 3800 cells per biopsy sample, demonstrating the feasibility of this method. From these analyses, we observed several cell-type differences between patients who achieved a pathological complete response (pCR) and patients who had residual disease (RD). Specifically, our data shows that tumor infiltrating lymphocytes are a potential prognostic biomarker of response to SG. Furthermore, we detected alterations in among stromal and immune cell subsets, among non-responders, indicating that these cell types maybe indicative of SG resistance. Taken together, we outline biomarkers of response to SG treatment for an improved understanding of resistance mechanisms in the neoadjuvant setting to improve TNBC outcomes among patients. Citation Format: Nicole Peiris, Simona Cristea, Mengran Zhang, Siang Koh, James Coates, Ilze Smidt, Veerle Bossuyt, Laura Spring, Aditya Bardia, Leif Ellisen. Utilizing scRNA sequencing to understand biomarkers of response and resistance to Sacitizumab Govetican in localized TNBC. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4353.