CAMBRIDGE, Mass. — Zai Lab Limited announced promising results from an early-stage clinical trial of its investigational cancer therapy, zocilurtatug pelitecan (zoci), demonstrating high tumor response rates and encouraging durability when combined with immunotherapy in patients with extensive-stage small cell lung cancer.
The findings from the global Phase 1b study will be presented at the European Society for Medical Oncology (ESMO) Congress 2026 in Madrid, Spain.
The trial evaluated zoci, formerly known as ZL-1310, in combination with the immunotherapy drug atezolizumab, both with and without the chemotherapy agent carboplatin, as an initial treatment for patients with extensive-stage small cell lung cancer.
According to Zai Lab, patients receiving the recommended Phase 3 dose of zoci at 1.6 mg/kg alongside atezolizumab achieved a confirmed objective response rate of 81.8%, with 27 of 33 patients experiencing measurable tumor shrinkage.
The six-month progression-free survival rate reached 81.9%, indicating that approximately eight in 10 patients remained alive without their disease worsening at that point.
Among 15 patients who had been followed for at least six months, median progression-free survival and median duration of response had not yet been reached after a median follow-up period of 10 months.
Ten of those 15 patients, or 66.7%, remained free from disease progression or death at the September 2026 data cutoff.
“Despite advances in treatment, extensive-stage small-cell lung cancer remains a devastating disease, with many patients experiencing disease progression within approximately five months of initiating standard first-line treatment,” said Rafael G. Amado, M.D., president and head of global research and development at Zai Lab.
“The high confirmed response rate, encouraging durability, and well-tolerated safety profile we are seeing with a standard chemotherapy-free regimen are particularly compelling. We believe zoci’s combination of efficacy and safety positions it to become an ADC backbone of choice in small-cell lung cancer, including in combination with immunotherapies,” Amado said.
The company reported that the two-drug combination was generally well tolerated, with most treatment-related adverse events classified as mild or moderate.
Severe adverse events related to zoci occurred in 9.1% of patients receiving the 1.6 mg/kg dose. No patients discontinued treatment because of treatment-related side effects, and researchers reported one mild case of interstitial lung disease or pneumonitis.
The most frequently reported side effects included anemia, nausea, reduced white blood cell counts, decreased appetite and elevated liver enzymes.
Researchers also evaluated a three-drug combination of zoci, atezolizumab and carboplatin in 13 patients across multiple dosing levels.
That regimen produced an objective response rate of 92.3%, with median progression-free survival reaching 8.4 months and median duration of response reaching 7.7 months.
However, the addition of carboplatin was associated with substantially higher rates of severe adverse events. Grade 3 or higher treatment-emergent adverse events occurred in 76.9% of patients receiving the three-drug regimen, compared with 21.2% of those receiving the two-drug combination at the recommended dose.
The findings suggest that the chemotherapy-free combination of zoci and atezolizumab may offer a potential treatment approach with fewer serious side effects, although larger randomized studies will be needed to confirm its effectiveness and safety compared with existing therapies.
Current first-line treatment for extensive-stage small cell lung cancer generally combines chemotherapy with an immune checkpoint inhibitor. Despite improvements in treatment, many patients experience disease progression within months.
Pedro Rocha, M.D., Ph.D., a study investigator and medical oncologist at Vall d’Hebron University Hospital in Barcelona, Spain, said the early findings support further investigation of the experimental combination.
“The zoci and atezolizumab doublet demonstrated substantial early antitumor activity with high, durable responses and a favorable safety profile, which are very encouraging results for patients with extensive-stage small cell lung cancer,” Rocha said.
“Importantly, this platinum-free regimen may allow patients to stay on treatment longer with potentially fewer side effects. These results support further exploration of zoci in combination regimens. I look forward to seeing how this profile evolves as the clinical program advances,” he added.
Zai Lab said it expects to begin a global, randomized Phase 3 clinical trial evaluating zoci in combination with an immuno-oncology treatment by the end of 2026.
The company is also exploring additional combinations involving zoci, including therapies designed to engage the immune system’s T cells in attacking cancer.
Zoci remains an investigational treatment, and its long-term clinical benefits and safety profile have not yet been established in a randomized Phase 3 study.
