Zai Lab Limited (NASDAQ:ZLAB) (HKEX:9688), a research-based, commercial-stage biopharmaceutical company based in China and the United States, on Friday reported promising initial results from a global Phase 1b trial evaluating zocilurtatug pelitecan (zoci, formerly ZL-1310) combined with atezolizumab, with or without carboplatin, as first-line treatment for extensive-stage small cell lung cancer (ES-SCLC).

At the recommended Phase 3 dose of 1.6 mg/kg, zoci plus atezolizumab achieved a confirmed objective response rate of 81.8% among 33 patients and an estimated six-month progression-free survival rate of 81.9%.

Among 15 patients with at least six months of follow-up, median progression-free survival and median duration of response had not been reached after a median follow-up of 10 months, with 66.7% remaining free of disease progression or death at the September 2026 data cut-off.

The doublet regimen showed a tolerability profile in which most adverse events were Grade 1 or 2; Grade 3 or higher adverse events related to zoci occurred in 9.1% of patients, with no treatment-related discontinuations and one Grade 1 case of interstitial lung disease or pneumonitis.

In a separate cohort of 13 patients receiving zoci, atezolizumab and carboplatin across multiple dose levels, the triplet regimen achieved an objective response rate of 92.3%, median progression-free survival of 8.4 months and median duration of response of 7.7 months. However, Grade 3 or higher treatment-emergent adverse events occurred in 76.9% of patients receiving the triplet, compared with 21.2% for the recommended-dose doublet regimen.

Zai Lab plans to initiate a global, randomised Phase 3 trial evaluating zoci combined with an immuno-oncology regimen as first-line treatment for ES-SCLC by the end of 2026. The Phase 1b findings are scheduled for presentation at the European Society for Medical Oncology Congress 2026 in Madrid.