Tehran University of Medical Sciences Acta Biochimica Iranica 0001-5261 3 2 2025 06 20 101 108 EN Hananeh Asghari Department of Biological Sciences, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan, Iran. Shiva Akbari-Birgani Department of Biological Sciences, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan, Iran. 3 Research Center for Basic Sciences and Modern Technologies (RBST), Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan, Iran. 2025 05 18 2025 07 09 Objectives: Triple-negative breast cancer (TNBC) is a hyperaggressive kind of breast cancer, due to its lack of therapeutic options, as it lacks hormonal receptors. Today, the only potential drug in the treatment of this subtype is chemotherapy, however drug resistance occurs after a while. In this study, we aimed to develop a co-culture organoid model to analyze the contribution of ''fibroblast'' on TNBC cell invasion and chemoresistance. Methods: A two-cell organoid model using the MDA-MB-231 cell line, a model cell for TNBC, and primary human foreskin fibroblasts (HDFs), was established. Their invasion and chemotherapy response were evaluated. Results: Our data shows that the fibroblasts made the invasion and chemoresistance easier. Hence, the important role of fibroblasts in modulating TNBC cell behavior was substantiated because the contribution of fibroblasts in TME was shown to promote invasion phenotype enhancement and decrease sensitivity to chemotherapy drugs. Conclusion: This study points out the significance of an organoid model in reproducing the tumor environment (TME), hence, it brings evidence for the involvement of fibroblasts in the formation of TNBC. Thereby, the increased drug resistance and invasion observed in organoids with fibroblasts further advocate the relevance of targeting the TME components when conceiving future therapeutic strategies for TNBC. https://abi.tums.ac.ir/index.php/abi/article/view/113 https://abi.tums.ac.ir/index.php/abi/article/download/113/103