Based on the facts that in colorectal cancer the JAK2/STAT3 signaling pathway is regulated by PGE2 [44], and STAT3 is not only involved in the expansion of CK14-positive stem cells in bladder cancer [47], but STAT3 activation in urothelial stem cells also leads to invasive bladder cancer progression, we decided to examine if metformin-inhibited bladder cancer development is through the COX2/PGE2/STAT3 axis. Here, STAT3 is linked to colorectal cancer.