As illustrated in Supplementary Fig. 4, the broad applicability of the synergistic effects of FGFR/HDAC co-inhibition for other FGFR-fusion positive solid tumors was established by examining a urothelial bladder cancer cell line (UBC), RT4, and an estrogen receptor-negative, progesterone receptor-negative, HER2-positive breast cancer cell line, SUM185PE, both of which harbor a FGFR3–TACC3 fusion commonly found in a number of solid tumors31. This evidence concerns the gene PGR and breast cancer.