Matrix metalloproteinases (MMPs) are a family of zinc endopeptidases capable of digesting the extracellular matrix (ECM), which is essential for tissue structure and transmitting messages between cells. MMPs play an important role in cancer, controlling cell migration, proliferation, apoptosis, regulation of tumour expansion, angiogenesis and invasion. Previous research has indicated high expression of MT1-MMP in breast cancers suggesting a potential role in tumour progression. Our results confirm that 3D multicellular tumour spheroids (MCTS) using phenotype-specific breast cancer cell lines are a valuable experimental model of the tumour microenvironment. Optimisation of MCTS culture growth conditions using different breast cancer cell lines (MCF-7, T47D, MDA-MB-468 and MDA-MB-231) was performed. Unexpected detection of MT1-MMP in MCF-7 MCTS warranted further investigation. MT1-MMP expression in different micro-environmental conditions, including hypoxia and nutrient deprivation (serum-free induced autophagy) were measured in MCF-7 monolayer cultures and MCTS models using immunofluorescence (IF), immunohistochemistry (IHC) and western blot (WB). MT1-MMP expression was rapidly and irreversibly up-regulated in MCF-7 breast cancer cells under conditions of stress (hypoxia and autophagy) compared to normal conditions suggesting an important role of the culture environment on cells behaviour and protein expression. We employed isobaric tags for relative and absolute quantitation (iTRAQ) technology to correlate MT1-MMP increase with proteomic profiles in MCF-7 breast cancer cell grown under hypoxic, serum-free and 3D MCTS conditions. More than 3500 proteins were identified, which were clustered into groups based on response to unique or shared microenvironment changes. Hypoxic monolayer and spheroid cells exhibited changes in anaerobic metabolism and lipid synthesis, respectively, whereas autophagy resulted in up-regulation of cellular component disassembly. The result indicated multiple drivers of MT1-MMP expression in MCF-7 cells. / Al-Mstansiriya University, Iraq