Further research using cells from invasive mammary cancer allowed to define CAFs as cells: (1) with explicit tumor-promoting activity, (2) containing a large fraction of α-smooth muscle actin (αSMA)-positive myofibroblasts co-existing with fibroblasts resembling those from normal tissues, (3) with proangiogenic capabilities, i.e., associated with augmented secretion of CXCL12/SDF-1, which were greater than those characterizing normal fibroblasts, and (4) with the preserved capacity to promote tumors and exert myofibroblastic features even in the absence of cancer cells [25]. Here, CXCL12 is linked to breast cancer.