ACTA1 and breast carcinoma: In breast cancer, these “myo CAFs” are particularly abundant and produce the desmoplastic response: a dense collagenous stroma responsible for the clinical presentation of a tumor as a ‘lump.’ As indicated by their name, “myo CAFs” resemble myofibroblasts and cells that appear after tissue lesion and are characterized by α-Smooth Muscle Actin (α-SMA) expression and secretion of ECM proteins [10,11].