ACTA1 and ductal breast carcinoma in situ: As α‐SMA expressing activated fibroblasts are master regulators of the ECM mechanobiology and central drivers that transform the tumor microenvironment,[4, 5, 6, 39, 70] we quantified their localization in the breast tissues with respect to untensed Fibronectin fibers, with a focus on invasive carcinomas, excluding DCIS where Fibronectin fiber relaxation was rarely observed.