Figure 1

A proposed model for the potential role of the interactions between tumor cells and inflammatory elements in breast cancer progression. The expression of monocyte chemoattractants (CCL5 and CCL2) by breast tumor cells may induce monocyte infiltration to breast tumor sites. The resulting tumor-associated macrophages (TAM) may express promalignant mediators, such as tumor necrosis factor alpha (TNF-α). This inflammatory cytokine may further promote the expression of tumor-supporting factors by the tumor cells, including matrix metalloproteinases (MMP) and the monocyte chemoattractants CCL5 and CCL2. The elevated expression of these chemokines by the tumor cells may result in additional monocyte recruitment, and in the stimulation of TAM at the tumor site. TAM stimulation may give rise to promoted levels of expression of promalignant factors, such as MMP, angiogenic mediators and TNF-α. Some of these activities may be stimulated directly by the chemokines. TAM-derived TNF-α may in turn further increase the expression of monocyte chemoattractants (e.g. CCL5, CCL2) by the tumor cells, and so on. This process may be aided by other functions of inflammatory cells/cytokines/chemokines (vascularization, release of growth factors, etc.; see Table 1) that eventually support the growth of the primary tumor and distant metastasis formation (possibly assisted by other chemokines, such as CXCL12).