© 2017 American Association for Cancer Research. Overcoming acquired drug resistance remains a core challenge in the clinical management of human cancer, including in urothelial carcinoma of the bladder (UCB). Cancer stem-like cells (CSC) have been implicated in the emergence of drug resistance but mechanisms and intervention points are not completely understood. Here, we report that the proinflammatory COX2/PGE2 pathway and the YAP1 growth-regulatory pathway cooperate to recruit the stem cell factor SOX2 in expanding and sustaining the accumulation of urothelial CSCs. Mechanistically, COX2/PGE2 signaling induced promoter methylation of let-7, resulting in its downregulation and subsequent SOX2 upregulation. YAP1 induced SOX2 expression more directly by binding its enhancer region. In UCB clinical specimens, positive correlations in the expression of SOX2, COX2, and YAP1 were observed, with coexpression of COX2 and YAP1 particularly commonly observed. Additional investigations suggested that activation of the COX2/PGE2 and YAP1 pathways also promoted acquired resistance to EGFR inhibitors in basal-type UCB. In a mouse xenograft model of UCB, dual inhibition of COX2 and YAP1 elicited a long-lasting therapeutic response by limiting CSC expansion after chemotherapy and EGFR inhibition. Our findings provide a preclinical rationale to target these pathways concurrently with systemic chemotherapy as a strategy to improve the clinical management of UCB. Significance: These findings offer a preclinical rationale to target the COX2 and YAP1 pathways concurrently with systemic chemotherapy to improve the clinical management of UCB, based on evidence that these two pathways expand cancer stem-like cell populations that mediate resistance to chemotherapy.