PURPOSE: We report phase I results for obrixtamig (BI 764532), a delta-like ligand 3 (DLL3)/CD3 IgG-like T-cell engager, in patients with previously treated DLL3-positive small cell lung cancer (SCLC), extrapulmonary neuroendocrine carcinomas (epNECs), or large cell neuroendocrine carcinoma of the lung (LCNEC-L).

METHODS: Patients received escalating intravenous obrixtamig doses using four regimens: a fixed dose once every 3 weeks (A); a fixed dose once weekly (B1); a step-up dose once weekly for two weeks and target dose once weekly (B2); and a step-up dose once weekly for 3 weeks, target dose once weekly for 3 weeks, and once every 3 weeks thereafter (B3). The primary objective was maximum tolerated dose (MTD). Secondary objectives included safety, pharmacokinetics, and tumor response (RECIST v1.1).

RESULTS: As of February 21, 2024, 168 patients received obrixtamig, 72% received ≥2 lines of previous anticancer therapy, and 51% received previous anti-PD-1/PD-L1 therapy. Seven dose-limiting toxicities occurred during MTD evaluation (Regimen A, n = 1; Regimen B2, n = 6). MTD was not reached. The most common treatment-related adverse event was cytokine release syndrome (any grade: 57%; grade ≥3: 3%); most cases occurred early and were reversible. Across all doses, regimens, and tumor types, the overall response rate (ORR) was 23% (95% CI, 17.4% to 30.2%), the median duration of response (DoR) was 8.5 months (95% CI, 6.2 to not reached), and the 6-month DoR rate was 70% (95% CI, 53% to 88%). All patients in Regimens B2/B3 received the minimum effective dose (≥90 μg/kg once weekly or once every 3 weeks), achieving an ORR of 28% (95% CI, 20.7% to 35.9%). With Regimens B2/B3, ORRs were 21% (95% CI, 12.9% to 33.1%), 27% (95% CI, 17.4% to 39.6%), and 70% (95% CI, 39.7% to 89.2%) for SCLC, epNECs, and LCNEC-L, respectively.

CONCLUSION: The demonstrated tolerability and efficacy of obrixtamig regimens, administered as step-up followed by target doses of 90-1,080 μg/kg (once weekly or once every 3 weeks), in patients with heavily pretreated DLL3-positive tumors support further exploration in SCLC, epNEC, and LCNEC-L.