This phenomenon of immune exclusion from tumours has been linked to the lack of patient response to PD-L1 blockade in many cancers, including metastatic urothelial cancer, and it is associated with a signature of transforming growth factor-β (TGF-β) signalling in fibroblasts,17 which is known to activate fibroblasts and induce the dense stromal reaction. Here, TGFB1 is linked to cancer.