ESR1 and breast cancer: Measuring several different biomarkers of phenotypic functional activities of MOs before and during their interplay with primary ER-/PR-/HER2+ breast cancer cells, we confirm scientific relevance of the co-culture system over the use of isolated cell types for analyzing the reversing effects of MET in a tumor-like microenvironment, where cancer cells usually alter immune cell functions, especially affecting their cell metabolism and ability for the production of antitumor cytokines, like co-operative cytokines IFN-γ and IL-10.