['Cancer-associated fibroblast (CAFs) are the most abundant cells in the tumor microenvironment, able to secrete growth factors and act on tumor progression. Melatonin is associated with several mechanisms of action with oncostatics and oncoprotectors effects, and also participate in the reduction of synthesis of surrounding fibroblasts and endothelial cells in breast cancer.', 'The objectives of this study were to determine the effectiveness of melatonin in cell viability and expression of proteins involved in angiogenesis and inflammation in triple-negative mammary tumor cell line (MDA-MB-231) and in co-culture with CAFs.', 'Cell viability was measured by MTT assay and the protein expression was evaluated by Membrane Antibody Array after melatonin treatment.', 'Melatonin treatment (1 mM) for 48 hours reduced the cell viability of MDA-MB-231, CAFs and co-culture (p < 0.05). The semi-quantitative protein analysis showed that when monoculture of tumor cells were compared with co-culture of CAFs, there was a regulation of angiogenic and inflammatory proteins (p < 0.05). Melatonin treatment also leads a differential expression of angiogenic and inflammatory proteins in both monoculture and co-culture of tumor cells and CAFs (p < 0.05).'] Does melatonin regulate angiogenic and inflammatory proteins in MDA-MB-231 cell line and in co-culture with cancer-associated fibroblasts?