ESR1 and bladder transitional cell carcinoma: 2 C). Further experiments were performed to examine the presence of the macrophage marker F4/80 and the VM marker PAS+/CD31- in BBN-induced BLCA tumors from ERα knockout (ERα-KO) and wild-type (WT) mice (Fig. 2I). The proportion of MIBC in WT samples was significantly higher than that in ERα-KO group (Fig. 2J). Our results showed that VM formation was significantly reduced in ERα-KO tumors compared with WT tumors (Fig. 2K) and there was a positive correlation between VM formation and macrophage infiltration (Fig. 2L).