TGFB1 and cancer: The additional TGFβ1 generated further amplifies the process potentially resulting in a cycle of TGFβ1 activation-fibroblast activation-extracellular matrix stiffening-TGFβ1 activation etc. Thus, cancers can progress to a point at which the tumour:stroma interaction develops into an activation loop whereby the upregulated αv integrins, increased matrix stiffness and probably proteases released by both tumour and myofibroblasts result in uncontrolled TGFβ1 activation.