Tumor microenvironment-mediated interactions between macrophages and cancer cells define immunoregulatory transcriptional programs.

Breast cancer progression is critically shaped by the tumor microenvironment, yet models that preserve patient-specific microenvironmental complexity remain limited. In particular, how the non-cellular microenvironment regulates macrophage-cancer cell crosstalk and contributes to tumor aggressiveness remains poorly understood. Here, we establish a patient-derived scaffold (PDS) model derived from decellularized breast cancer tissues as a platform to interrogate these interactions. Growth of MDA-MB-231 and MCF-7 cancer cells in PDSs reshaped cytokine gene expression and secretory profiles, leading to transcriptional reprogramming of THP-1 monocytes. Additionally, THP-1 cells were able to infiltrate PDSs and adopted macrophage-like states characterized by increased expression of M2- and pluripotency-related genes, alongside reduced proliferation signatures. Strikingly, transcriptional analysis of THP-1 PDS cultures identified a subset of PDSs derived from estrogen receptor-negative, CD163high tumors that preferentially induced upregulation of gene programs associated with macrophage differentiation and immunoregulatory gene signatures. Secreted molecules from these THP-1 PDS cultures, in turn, enhanced epithelial-to-mesenchymal transition (EMT)-related and immune-associated gene expression in cancer cells, particularly in MDA-MB-231, revealing transcriptional crosstalk linked to aggressive tumor features. Together, our findings demonstrate that the non-cellular tumor microenvironment preserved in PDSs is sufficient to drive coordinated transcriptional programs in both macrophages and cancer cells. The strong concordance between PDS-induced responses and clinical tumor characteristics underscores the potential of PDS-based models to uncover patient-specific tumor microenvironment interactions and guide future strategies targeting macrophage-cancer cell crosstalk in breast cancer.