Transcriptomic analysis of the tumor immune microenvironment (TIME) in patients with breast cancer with liver metastasis (BCLM).

e13045 Background: Breast cancer with liver metastasis (BCLM) is a significant predictor of worse prognosis and poor overall survival. Liver specific homing of breast cancer is not well understood, and the tumor immune microenvironment (TIME) likely plays a critical role in the process of forming BCLM. This retrospective study was conducted to determine the clinical risk factors and transcriptomic biomarkers associated with BCLM. Methods: A retrospective single institute chart review was conducted. Patient, disease characteristics and treatment variables were reviewed. Liver metastasis specific survival (defined by overall survival time from the diagnosis of liver metastasis) were compared across three breast subtypes (i.e., ER+/HER2-, HER2+, and triple-negative (TN) breast cancer) using Kaplan-Meier curves. Next generation sequencing (NGS) via commercial platforms were then used to obtain transcriptomic data. Transcriptomic analysis including differential gene expression analysis, gene set enrichment analysis (GSEA), as well as gene deconvolution analysis with TIMER2.0 were conducted for comparison of transcriptomic profiles and immune compositions across the three breast cancer subtypes. Results: 176 patients with BCLM and available liver metastasis biopsy were identified through retrospective chart review. Liver metastasis specific survival was compared, HER2+ BCLM patients (n = 17) had the best outcome and TN BCLM patients (n = 46) had the worst outcome with ER+ BCLM patients (n = 112) in the middle (p < 0.0001, ER+ vs TNBC p < 0.0001, ER+ vs HER2+ p = 0.038, HER2+ vs TNBC p = 0.00011). Principle component analysis on the transcriptomic data of 30 liver metastatic samples revealed different expression profiles between ER+ (n = 20) and TN (n = 7) BCLM, while HER2+ (n = 3) BCLM did not shown statistical differences with either group. B cell mediated immunity was upregulated in TN BCLM compared to ER+HER2- BCLM by GSEA (normalized enrichment score = 2.35, adjusted P-value = 0.19). Consistently, plasma cells were relatively enriched in TN BCLM compared to ER+ and HER2+ BCLM (p = 0.037) based on CIBERSORT estimation. In contrast, monocytes and neutrophils were enriched in ER+ BCLM (p = 0.0093 & 0.018) based on TIMER2.0 estimation. Additional NGS analysis is currently underway for increased sample size. Conclusions: BCLM in TNBC was associated with significantly worse overall survival. TIME in TN BCLM enriched for genes associated with B cell mediated immunity while ER+ BCLM had more monocyte/neutrophil mediated immunity.