An FGFR3/MYC positive feedback loop provides new opportunities for targeted therapies in bladder cancers.

FGFR3 alterations (mutations or translocation) are among the most frequent genetic events in bladder carcinoma. They lead to an aberrant activation of FGFR3 signaling, conferring an oncogenic dependence, which we studied here. We discovered a positive feedback loop, in which the activation of p38 and AKT downstream from the altered FGFR3 upregulates mRNA levels and stabilizes MYC protein, respectively, leading to the accumulation of MYC, which directly upregulates expression by binding to active enhancers upstream from Disruption of this FGFR3/MYC loop in bladder cancer cell lines by treatment with FGFR3, p38, AKT, or BET bromodomain inhibitors (JQ1) preventing transcription decreased cell viability and tumor growth A relevance of this loop to human bladder tumors was supported by the positive correlation between and levels in tumors bearing mutations, and the decrease in FGFR3 and MYC levels following anti-FGFR treatment in a PDX model bearing an mutation. These findings open up new possibilities for the treatment of bladder tumors displaying aberrant FGFR3 activation.