TGFBR2 and bladder transitional cell carcinoma: Interestingly, secreted GDF15 consequently not only further upregulates CSC-related gene expression but also induces the activation of cancer-associated fibroblasts through the transforming growth factor beta receptor type 2 (TGFBR2)-transforming growth factor β (TGFβ)-TGFBI self-regulatory feedback loop to promote stemness in BLCA.