CAF activation is triggered by a variety of stimuli, including cancer cell‐derived TGF‐β1, PDGFα, PDGFβ, basic FGF (bFGF, also known as FGF2), and IL‐6,72, 73, 74, 75, 76 and environmental stimuli, such as hypoxia, oxidative stress, and matrix stiffness.52, 77, 78 All these stimuli may cooperate to determine different CAF phenotypes further contributing to their heterogeneity. Here, TGFB1 is linked to cancer.