The immunocytochemical analysis for α-SMA, demonstrated that the highly invasive and metastatic MDA-MB-231 cells, when co-cultured with CAFs for 6 days, induced a sharp increase in the amount of α-SMA-positive stromal elements, indicating the acquisition of a myofibroblast-like phenotype, typical of the breast tumor stroma (Figure 3). The gene discussed is ACTA1; the disease is breast neoplasm.