These contrasting functions suggest that the members of the TGF-β family may establish an equilibrium state, which is disrupted within the tumour microenvironment because tumour cells can excessively express autocrine TGF-β1 [25, 26], which can lead to further production of an abundance of miR-21 and generate a feed-forward loop in cancer progression. Here, TGFB1 is linked to cancer.