Figure 3. Breast tumor cell induction of α-smooth muscle actin (α-SMA) in tumor stroma-derived fibroblasts.

Sections (10 µm) of paraformaldehyde-fixed frozen nodule culture (CAFs) and co-cultures (MCF-7 or MDA-MB-231 breast tumor cells with CAFs) at day 6 of culture are shown. Sections were stained immunohistochemically using an anti-α-SMA monoclonal antibody to verify the effect of breast cancer cells on fibroblast-to-myofibroblast transdifferentiation. α-SMA expression was induced in the tumor-associated fibroblast population as a result of the interaction with the more aggressive and less differentiated MDA-MB-231 cells, demonstrating the ability of these cells to promote stroma activation. DAB for detection; hematoxylin counterstaining; original magnification, ×200.