An interesting study by Nguyen et al. used recent advances in microtechnology of “organ-on-chip” to reproduce ex vivo the complexity of the tumor microenvironment ecosystems integrating the main populations of BrCa stroma: immune cells, endothelial cells and fibroblasts, together with BT-474 HER2+ BrCa cells, in the absence or presence of trastuzumab. Here, ERBB2 is linked to invasive breast carcinoma.