Evolving knowledge about the tumor-immune microenvironment (TIME) is driving innovation in designing novel therapies against hard-to-treat breast cancer. Targeting the immune components of TIME has emerged as a promising approach for cancer therapy. While recent immunotherapies aim at restoring antitumor immunity, counteracting tumor escape remains challenging. Hence there is a pressing need to better understand the complex tumor-immune crosstalk within TIME. Considering this imperative, this study aims at investigating the crosstalk between the two abundant immune cell populations within the breast TIME-macrophages and T cells, in driving tumor progression using an organotypic 3D in vitro tumor-on-a-chip (TOC) model. The TOC features distinct yet interconnected organotypic tumor and stromal entities. This triculture platform mimics the complex TIME, embedding the two immune populations in a suitable 3D matrix. Analysis of invasion, morphometric measurements, and flow cytometry results underscores the substantial contribution of macrophages to tumor progression, while the presence of T cells is associated with a deceleration in the migratory behavior of both cancer cells and macrophages. Furthermore, cytokine analyses reveal significant upregulation of leptin and RANTES (regulated on activation, normal T Cell expressed and secreted) in triculture. Overall, this study highlights the complexity of TIME and the critical role of immune cells in cancer progression.