20P Spatial Analysis of Residual Tumor Tissue Provides New Clues for Post-Neoadjuvant Treatment Approaches in Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is a very heterogeneous disease with high metastatic recurrence risk. We showed (PMID 34535679) that TNBCs relapsing rapidly (RR) after NACT (in ≤ 12 months) are highly proliferative, immune-cold, often with large residual cancer burden (RCB) and fatal outcome. No specific biomarkers or therapeutic targets are known for this clinical category. In this study we performed spatial molecular analysis of the RR and the RCB3 TNBCs, with the aim to help improving treatment of the TNBC patients with the poorest prognosis. We analyzed residual tumor tissue samples of TNBC patients treated by standard NACT from 01/01/2009 to 31/12/2021. The cases were classified into RR, standardly-relapsing (SR, 1-5 years post-NACT) and without recurrences (NR). The amount of tumor-infiltrating lymphocytes (TILs) was determined by optical microscopy (H&E). Tissue protein expression was spatially resolved by GeoMx® Digital Spatial Profiler (NanoString Technology). Sixteen, 17 and 47 RR, SR and NR cases were analyzed, respectively. GeoMx analysis included 216 Region-of-Interest (ROIs) of tumor microenvironment (TME) and 207 of tumor cells (TC), with balanced (∼50/50) numbers of peripheral (P) and central (C) ROIs. Tumors and ROIs were classified into TIL-rich (LR) and TIL-poor (LP) using cut-off of 10% TILs. The RR TNBCs showed higher Ki67, cleaved caspase 9, granzyme B (GZMB), FoxP3 and fibronectin (FBNCT) in TME-P-LR ROIs but higher GADPH, TIM-3, PD-L1 and IDO in TME-P-LP ROIs. Compared to TNBC-SR, the RR had higher GZMB and CD34 in TME-P-LR ROIs. In TME-C-LR ROIs of the RRs, CD8 expression was low, as well as the one of CD45, CD3 and CD8 in TME-C-LP. The RCB3 category contained 9, 8 and 10 RR, SR and NR cases, respectively. Although most RCB3 cases were TIL-poor, the NR cases showed significantly higher expression of CD3, CD8, GZMA, CD4, CD56, CD95, LAG3, HLA-DR, BIM and BCL6 than the RR cases. By this study we revealed several potential therapeutic targets (fibronectin, IDO, TIM-3, CD34 /angiogenesis) in the RR TNBCs. Interestingly, we also showed that some RCB3 cases have immune-activated TME and good prognosis. Spatial tissue analysis was crucial for these discoveries.