Background: Datopotamab deruxtecan (Dato-DXd) is an antibody-drug conjugate consisting of a humanized anti-TROP2 IgG1 monoclonal antibody covalently linked to a highly potent topoisomerase I inhibitor payload via a plasma-stable, tumor-selective, tetrapeptide-based cleavable linker. Dato-DXd has shown encouraging antitumor activity and a manageable safety profile in patients (pts) with solid tumors. We report preliminary results in pts with advanced/metastatic (a/m) urothelial cancer from the ongoing phase 1 TROPION-PanTumor01 study (NCT03401385). Methods: Pts with unresectable a/m urothelial cancer treated with ≥1 prior line of therapy received intravenous Dato-DXd 6 mg/kg Q3W. Primary study objectives were safety and tolerability. Secondary endpoints were objective response rate (ORR; complete response [CR] + partial response [PR]), and disease control rate (DCR; CR + PR + stable disease) per RECIST 1.1 by BICR. This is the first data disclosure from this cohort in an ongoing expansion cohort study. Results: At data cutoff (May 18, 2023), 18 pts had received Dato-DXd. Median follow-up was 9.1 (range 5–17) months; 6 (33.3%) pts were receiving ongoing treatment. Median age was 63.5 (range 46–79) yrs. Pts were heavily pretreated, 15 (83.3%) had received ≥3 prior regimens. All pts received prior immunotherapy, 17 (94.4%) prior platinum-based chemotherapy, and 4 (22.2%) prior taxanes. Treatment-emergent adverse events (TEAEs) occurred in 100% (any grade [gr]) and 44.4% (gr ≥3) of pts, and drug-related TEAEs occurred in 94.4% (any gr) and 16.7% (gr ≥3) of pts. No drug-related serious AEs were reported, and no TEAEs associated with death were observed. Any gr TEAEs associated with reduction, interruption, and discontinuation of treatment were reported in 11.1%, 33.3%, and 5.6% of pts, respectively (Table). Adjudicated drug-related interstitial lung disease (gr 2) occurred in 1 (5.6%) pt. Confirmed ORR was 27.8% (95% CI 9.7–53.5); 1 pt achieved a CR and 4 achieved a PR. DCR was 77.8% (95% CI 52.4–93.6). Clinical evaluation of this cohort is ongoing and updated results will be presented. Conclusions: In heavily pretreated pts with a/m urothelial cancer, Dato-DXd demonstrated a tolerable and manageable safety profile with encouraging antitumor activity. Dato-DXd is being evaluated in pts with urothelial cancer as part of the phase 1/2 TROPION-PanTumor02 (NCT05460273) and the phase 2 TROPION-PanTumor03 (NCT05489211) studies. Clinical trial information: NCT03401385.

*Stomatitis (n=2), lymphocyte count decreased (n=1). SAE, serious adverse event; TEAE, treatment-emergent adverse event.