Recently, the 2026 European Society for Medical Oncology (ESMO) congress was held in Madrid, Spain, drawing widespread attention from the international academic community, while global secondary-market investors also actively scouted for investment opportunities within it. According to Zhitong Finance APP observations, on October 23, the U.S.-listed share price of Zai Lab Ltd (NASDAQ: ZLAB) surged, with intraday gains reaching as high as 11.12%; trading volume that day hit 3.6915 million shares, a new high in nearly two months, corresponding to a turnover of US$86.9231 million, reflecting markedly warming trading enthusiasm on the floor. The positive secondary-market reaction stemmed from the company's presentation that day at the ESMO congress of the first data from a global Phase Ib clinical study evaluating zocilurtatug pelitecan (Zoci, formerly ZL-1310) in combination with atezolizumab (with or without carboplatin) for first-line treatment of extensive-stage small cell lung cancer (ES-SCLC). Its striking data results won broad recognition from the global academic community and capital markets, and also left investors full of expectations for the product's future global commercialization prospects. Investment bank Cantor published a research report arguing that the data Zai Lab's DLL3 ADC Zoci unveiled this time in first-line extensive-stage small cell lung cancer has already reached "Home Run" level, while a thoracic oncology expert from NYU Grossman School of Medicine who joined the discussion is bullish on Zoci replacing first-line chemotherapy, seeing potential to change the first-line treatment landscape and gradually grow into a backbone therapy for small cell lung cancer.

Striking Clinical Data, Another Step Toward "Chemotherapy-Free"

As a DLL3-targeting ADC drug developed internally by Zai Lab Ltd (NASDAQ: ZLAB) and independently advanced through global clinical trials, and also one of the fastest-moving DLL3 ADCs worldwide, Zoci has enjoyed high exposure at international authoritative conferences since entering Phase I clinical trials, demonstrating broad therapeutic prospects in small cell lung cancer and neuroendocrine tumors. In less than two years, Zai Lab advanced Zoci from the first-in-human (FIH) investigational new drug (IND) application to the global Phase III registrational study stage, and obtained orphan drug designation and fast track designation from the U.S. FDA, orphan drug designation from the European EMA, and breakthrough therapy designation from China's National Medical Products Administration, fully demonstrating that it has won unanimous recognition from the global industry and authoritative regulatory agencies, and also reflecting the outstanding collaborative capabilities and clinical development efficiency of Zai Lab's global team. Against this backdrop, Zai Lab bringing Zoci's latest research results in first-line treatment of small cell lung cancer to this year's ESMO annual meeting undoubtedly became a focal point of industry attention. According to Zhitong Finance APP, the data Zai Lab disclosed this time came from a global Phase Ib study evaluating Zoci in combination with atezolizumab for first-line treatment of extensive-stage small cell lung cancer (ES-SCLC), with two regimens in total: a chemotherapy-free "dual-drug regimen" (Zoci + atezolizumab), and a "triple-drug regimen" adding carboplatin on that basis. The dual-drug regimen is the core of this data release. At the recommended Phase III study dose (RP3D) of 1.6 mg/kg (n=33), the confirmed objective response rate (ORR) of the dual-drug regimen reached 81.8%, with a 6-month progression-free survival rate of 81.9%. Responses not only arrived quickly but also lasted long. Among 15 patients followed for at least 6 months, at a median follow-up of 10 months, both median progression-free survival (mPFS) and median duration of response (mDoR) had not yet been reached, with 10 patients (66.7%) still free of disease progression. Safety was likewise a highlight of the dual-drug regimen. At the 1.6 mg/kg dose, adverse events related to Zoci were mostly Grade 1 or Grade 2; the incidence of Zoci-related Grade 3 or higher adverse events (TRAEs) was only 9.1%, with no treatment-related discontinuations and no treatment-related deaths, and only 1 case of interstitial lung disease (ILD)/non-infectious pneumonitis, which was Grade 1. By comparison, the triple-drug regimen (n=13, pooling multiple dose levels) had a confirmed ORR of 92.3%, an mPFS of 8.4 months, and an mDoR of 7.7 months. But adding carboplatin markedly increased toxicity: the incidence of Grade 3 or higher treatment-emergent adverse events (TEAEs) rose from 21.2% for the dual-drug regimen to 76.9%, predominantly hematologic toxicity. In short, the chemotherapy-free dual-drug regimen achieved a better balance among efficacy, durability, and safety; while adding platinum-based chemotherapy buys a higher response rate, it also brings a clearly heavier burden of hematologic toxicity. This is also why the dual-drug regimen became the focus of subsequent development. In fact, the current standard first-line treatment for small cell lung cancer is immune checkpoint inhibitors combined with chemotherapy, with a response rate of 60-70%, a median progression-free survival of about 5 months, and approximately 60% Grade 3 or higher treatment-related adverse events. Compared with that (cross-trial indirect comparison, not head-to-head), the data performance of Zoci combined with atezolizumab's dual-drug regimen under completely chemotherapy-free conditions conveys a key signal: a chemotherapy-free regimen with Zoci as its backbone is expected to deliver better safety and more durable disease control while matching platinum-based chemotherapy in efficacy, pushing first-line ES-SCLC treatment one more step toward "chemotherapy-free." This approach also extends to combination development. According to Zhitong Finance APP, this year Zai Lab Ltd (NASDAQ: ZLAB) reached a global clinical research collaboration with Amgen to evaluate zoci in combination with IMDELLTRA® (tarlatamab, a DLL3/CD3 bispecific TCE) for extensive-stage small cell lung cancer; and reached a clinical research collaboration with Boehringer Ingelheim to evaluate Zoci in combination with Obrixtamig (a DLL3/CD3 bispecific TCE) for small cell lung cancer and other neuroendocrine cancers. The fact that two multinational pharmaceutical companies holding DLL3 TCEs successively chose to combine them with Zoci has a mechanistic basis: Zoci directly kills tumor cells by internalizing the ADC and releasing its payload, independent of T cells, complementing the killing pathway of T-cell engagers. This also indirectly reflects that Zoci leads in development within the DLL3 ADC field and has the potential to serve as a backbone drug for combination therapy.

Leading Global Development, Continuously Expanding the Boundaries of Clinical Value

From a market perspective, the global lung cancer treatment market continues to expand, projected to grow to US$76.6 billion by 2030, with small cell lung cancer accounting for about 15% of confirmed lung cancer cases worldwide. Of the roughly 250,000 new SCLC cases globally each year, about two-thirds are already at extensive stage (ES-SCLC) at diagnosis, and they also face a severe burden of brain metastases. Although first-line immunotherapy plus chemotherapy has raised median overall survival (OS) in ES-SCLC to 12-15 months, long-term survival rates remain extremely low, with 5-year survival hovering at only 5%-10%. It can thus be seen that treatment for small cell lung cancer, especially extensive-stage small cell lung cancer, still has very substantial room for improvement, and clinical need is extremely urgent. In recent years, targets such as DLL3, B7-H3, and SEZ6 that are highly expressed on SCLC tumor cells have been successively identified, becoming important directions for ADC development and giving rise to a batch of highly promising ADC drug candidates. Among them, DLL3 is highly expressed in SCLC and lowly expressed in normal tissues, making it one of the targets considered to have strong specificity. Zoci is precisely one of the world's leading ADCs in development against this target. In terms of development progress, Zoci took less than two years to advance from the first-in-human IND to a global Phase III study, with both second-line and first-line already in or about to enter global registrational studies, placing its R&D and registration progress in the first tier of global first-line SCLC competition. According to Zhitong Finance APP, Zai Lab Ltd (NASDAQ: ZLAB) plans to submit its first indication marketing application for Zoci to the U.S. FDA in 2027. If all goes smoothly, Zoci is expected to become the world's first approved DLL3 ADC.

Conclusion

The data disclosed at this ESMO annual meeting show that Zoci combined with atezolizumab's chemotherapy-free regimen combines a high response rate, positive durability signals, and outstanding safety, providing strong early evidence for its entry into first-line ES-SCLC and for advancing "chemotherapy-free" treatment. Whether it can become a first-line "backbone therapy" for small cell lung cancer will ultimately be answered by Phase III overall survival data. But these ESMO data at least show that replacing first-line chemotherapy with a safer ADC is no longer merely a hypothesis. From second-line to first-line, and from monotherapy to combinations, Zoci's development path is gradually becoming clearer.