In vivo, genetic or pharmacological ablation of prolyl hydroxylase 2 (EGLN1 also known as PHD2), which stabilizes the transcription factor HIF1α, in CAFs cotransplanted orthotopically with 4T1 breast cancer cells decreased tumor stiffness, invasion and liver metastasis.93 Accordingly, HIF1α‐depletion,94 but not depletion of PHD2,95 in fibroblasts before tumor onset accelerates tumorigenesis in a MMTV‐PyMT model. Here, HIF1A is linked to breast carcinoma.