TNF and neoplasm: In both tumor cell lines and in the monocytic cell line, presence of TNFα was necessary to induce MMP-9 secretion in each of the single cultures, however, the co-cultures significantly elevated this level, synergistically for the A498 cells (5-folds, p < 0.001) and additively for the MCF-7 cells (1.6-folds, p < 0.001, Figure 1D).