FN1 and ductal breast carcinoma in situ: Using our peptide tension probe FnBPA5, whose nm affinity to Fibronectin fibers is destroyed by fiber stretching,[51, 56, 57] we discovered here that Fibronectin fibers have partially lost their tension in invasive human tumor stroma in locations that are in close proximity to α−SMA positive myofibroblastic CAFs, as well as T‐cells and cancer cells, whereas they are still mostly tensed in DCIS and in healthy breast tissues (Figures 1, 2).