Comprehensive Analysis of JCHAIN as a Potential Prognostic Factor for Breast Cancer and an Indicator for Tumor Microenvironment

<b>Background</b>: Breast cancer remains a predominant malignancy among females globally, and the tumor microenvironment (TME) exerts a pivotal role in its progression. Despite notable advancements in diagnostic and therapeutic modalities, resistance to conventional therapies persists as a critical hurdle, underscoring the necessity of exploring TME-related prognostic biomarkers. <b>Methods</b>: To elucidate the role of the TME in breast cancer progression and identify potential prognostic biomarkers, we analyzed RNA-seq data from 1081 breast cancer cases and 99 normal controls to assess tumor-infiltrating immune cells (TICs) and stromal components. Differential gene expression analysis identified genes correlated with ImmuneScore and StromalScore. A protein-protein interaction (PPI) network was constructed, followed by univariate Cox regression to pinpoint survival-associated genes. JCHAIN, significantly linked to survival outcomes, was selected for further investigation. Gene Set Enrichment Analysis (GSEA) and TIC correlation analyses were performed to explore its associations with immune pathways. Additionally, immunohistochemistry (IHC) and multiplexed immunofluorescence (mIF) were performed on 61 clinical samples. <b>Results</b>: High ImmuneScore was associated with improved survival. Joining chain of multimeric IgA and IgM (JCHAIN) expression was notably reduced in tumor tissues, with low expression correlating with poorer prognosis. GSEA highlighted immune-related pathways enriched in high JCHAIN expression groups. TIC analysis revealed positive correlations with CD8+ T cells and M1 macrophages. IHC and mIF validations further confirmed decreased JCHAIN protein expression in tumor tissues, and higher JCHAIN expression was associated with increased M1 macrophage density. <b>Conclusions</b>: JCHAIN serves as a promising prognostic biomarker in breast cancer, reflecting immune activity within the TME, providing valuable insights into immune-stromal interactions and the therapeutic potential of JCHAIN.