Background: EV is FDA-approved in pts with aUC and ≥1 prior therapy line. Data from EV-103 trial indicate robust response to first-line EV/pembrolizumab, suggesting potentially at least additive treatment effect with EV/ICI combination. Given the long half-life of ICIs, pts who start EV treatment immediately after ICI may potentially derive benefit from that therapy sequence. We hypothesized that the last systemic therapy prior to EV would impact outcomes, as pts treated with ICI immediately prior to EV would have superior outcomes relative to pts treated with chemotherapy (chemo). Methods: UNITE is a retrospective study of pts treated with EV at 16 US sites. Pt characteristics and outcomes were abstracted from EMR review at each site. Observed response was determined by investigators for evaluable pts with scans following ≥1 EV dose. Pts treated with EV monotherapy were divided into two groups based on whether they received chemo or ICI as the line of therapy immediately prior to EV, regardless of other therapy received. Chi-squared test was used to assess differences in pt characteristics and ORR while log-rank tests were used for OS and PFS measured from EV start. Results: Among 325 pts treated with EV monotherapy, 247 had chemo or ICI as immediate prior treatment, with 186 pts receiving ICI (Group A) and 61 pts receiving platinum-based chemo (Group B). In 247-pt cohort, ORR to EV was 52% and mPFS and mOS were 6 and 13 mos. Group B pts were younger, had more bone mets and higher Bellmunt risk factors, but were otherwise similar to Group A (Table). Most pts had both prior chemo and ICI in both group A (58%) and group B (84%). Group A pts had shorter time from last treatment (median 1.2 vs 3.2 mo, p<0.01), lower ORR to immediate prior treatment (16% vs 37%, p<0.01) and fewer prior therapy lines (mean 1.9 vs 2.6, p<0.01). Group A had superior ORR (58% vs 37%, p=0.02), mPFS (6.9 vs 4.8 mo, p=0.02) and mOS (15.2 vs 8.8 mo, p=0.01) from EV start vs Group B. Conclusions: Pts with aUC treated with EV had superior outcomes if they received ICI instead of chemo as immediate prior treatment, suggesting the hypothesis that this may represent an optimal therapy sequence or combination. These data need external validation as limitations include retrospective design, lack of randomization, and selection and confounding biases.