HIF1A and breast cancer: Thus, the ECM deposited by hypoxic fibroblasts promoted changes in morphology, adhesion, and migration of breast cancer cells and enhanced invasion.91 Moreover fibroblasts expressing activated hypoxia‐inducible factor 1 alpha (HIF1α) were pro‐tumorigenic and pro‐metastatic when cotransplanted in MDA‐MB‐231 xenografts.92 Conversely, hypoxia decreased expression of α‐SMA and impaired contractile forces and the ability to remodel the ECM in vulval and head and neck SCC CAFs cultured in 3D collagen gels.