TGFB1 and neoplasm: In gastrointestinal polyposis, it is the loss of the Lkb1 gene from surrounding mesenchymal stroma (not the tumour) that causes tumour formation due to reduced TGFβ production by stromal cells that support the tumour, and defective TGFβ-signalling in epithelial cells, coinciding with their subsequent enhanced proliferation29.