- BACKGROUND: The renin-angiotensin system is involved in the regulation of angiogenesis and cell proliferation. Angiotensin inhibition may improve drug delivery by enhancing tumor perfusion partly by downregulating transforming growth factor (TGF)-β. Because TGF-β is associated with resistance in patients with metastatic urothelial carcinoma (mUC) receiving programmed cell death protein 1/programmed cell death ligand 1 (PD1/L1) inhibitors, we hypothesized that angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs) may enhance the outcomes of patients with mUC who receive PD1/L1 inhibitors. PATIENTS AND METHODS: Data from patients with mUC who received PD1/L1 inhibitors as monotherapy were obtained; patients from the Dana-Farber Cancer Institute constituted the discovery dataset, and data from Moffitt Cancer Center served as the validation dataset. A logistic regression investigated the impact of concurrent ACEI/ARB primarily on any regression of tumor (ART) after controlling for prognostic factors. RESULTS: Data were available for 178 patients from the discovery dataset, of whom 153 (86%) had received prior platinum and 33 (18.5%) concurrent ACEIs/ARBs. Multivariable logistic regression analysis revealed that ACEIs/ARBs were associated with greater probability of ART (odds ratio [OR] = 2.69; 95% confidence interval [CI], 1.15-6.30; P = .022). In the validation dataset, 101 patients were available, of whom 59 (58.4%) had received prior platinum and 22 (21.8%) concurrent ACEIs/ARBs. ACEI/ARB demonstrated a trend for association with ART (OR = 3.28; 95% CI, 0.98-10.99; P = .054) on multivariable analysis of the validation dataset. CONCLUSIONS: Concurrent angiotensin blockade was associated with a higher rate of tumor regression in patients with mUC receiving PD1/L1 inhibitors. Validation is warranted in a prospective trial, especially given the cost efficacy of ACEIs/ARBs.