Abstract PO2-25-03: Deciphering the immune molecular signature associated with pembrolizumab efficacy in the neoadjuvant setting of Triple-Negative Breast Cancer patients: a single-centre experience

Abstract Triple-negative breast cancer (TNBC) accounts for 15-20% of all breast cancers and is characterized by a high rate of recurrence, despite the improvement of the therapeutic approaches in recent years. Neoadjuvant chemotherapy (NACT) is the standard treatment for early-stage TNBC. Achieving a pathological complete response (pCR) is considered an essential prognostic factor for long-term outcomes. However, the percentage of pCR patients after NACT is limited to 30-40%, thus requiring the implementation of novel therapeutic strategies. Recently, by applying a morphology-guided spatial transcriptomic approach on Tru-Cut biopsies, we showed that intratumoral infiltrating lymphocytes (iTILs) and stromal Natural Killer (NK) cells are major determinants of chemotherapy efficacy in TNBC. These data highlight a complex three-dimensional organization of the tumor landscape and underline how spatiality and molecular activation of immune cells are essential to enhance the efficacy of neoadjuvant NACT in TNBC. The fact that immune cells are important players in this setting is corroborated by the clinical success shown by the KEYNOTE-522 study. This trial paved the way for the use of immunotherapy in neoadjuvant settings, obtaining a significant improvement in the patient’s overall response compared to standard NACT. Still, the implementation of chemotherapy with immunotherapy in the TNBC neoadjuvant treatment implicates several compelling questions, including how to further increase the percentage of patients with a complete response, overcoming resistance mechanisms, and how to improve the personalization of treatment, evaluating which patients can benefit from a therapy de-scalation or another combined therapeutic strategy. In this prospective cohort study, we decided to define the relevance of different immune populations in affecting pembrolizumab efficacy in the neoadjuvant treatment of TNBC patients. We treated 40 patients with an early-TNBC diagnosis with the KEYNOTE-522 regimen that consists of four cycles of an intravenous infusion of pembrolizumab plus paclitaxel and carboplatin, followed by four cycles of pembrolizumab plus epirubicin and cyclophosphamide. Only patients with evident side effects to immunotherapy administration were a priori excluded. Currently, 18 patients ended the neoadjuvant schedule and underwent surgical excision. Our data indicate that 15 patients displayed a pCR at the end of the therapy, whereas 3 patients displayed only partial response. To further clarify the immune dynamics that lead to a complete response to pembrolizumab in these patients, we collected peripheral blood before and after neoadjuvant treatment to isolate peripheral blood mononucleated cells (PBMCs). We applied a single-cell transcriptome analysis to shape any variations in circulating immune cells occurring during neoadjuvant treatment and associated with patient response. In addition, we collected residual tumors at surgery from partial responders and derived three-dimensional organoids that recapitulate the characteristics of the original patient tumor. These ex vivo organoid-based platforms are applied to clarify the molecular mechanisms driving neoadjuvant resistance. To this aim, we are performing co-cultures with autologous immune cells to identify novel combined therapeutic strategies to rescue pembrolizumab efficacy in these models. Overall, our study is defining the immune-related molecular mechanisms driving pembrolizumab and chemotherapy response in the neoadjuvant treatment of TNBC patients. Our findings can improve our understanding of which immune populations are determinant players in anti-TNBC immune response and can be proposed as novel biomarkers of pembrolizumab efficacy during the neoadjuvant treatment. Citation Format: Elisa Gasparini, Gloria Manzotti, Moira Ragazzi, Benedetta Donati, Federica Torricelli, Elisa Salviato, Alessandra Bisagni, Eleonora Zanetti, Alessandra Bologna, Saverio Coiro, Rita Vacondio, Guglielmo Ferrari, Giancarlo Bisagni, Carmine Pinto, Alessia Ciarrocchi, Francesca Reggiani. Deciphering the immune molecular signature associated with pembrolizumab efficacy in the neoadjuvant setting of Triple-Negative Breast Cancer patients: a single-centre experience abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-25-03.