FN1 and breast cancer: High‐grade carcinomas tend to have an increased tumor cell density and cell size (Figure 5C,D; Figure S6, Supporting Information), in agreement with the literature, where tumor cells are expected to be more proliferative, compared to intermediate‐grade tumors.[74] These data show for the first time that tumor grade in invasive human breast cancers correlates with an enhanced presence of untensed Fibronectin fibers, with Fibronectin fibers undergoing progressive relaxation as tumor grade increases.