AstraZeneca Advances Phase 3 Trial Combining Arcus' TIGIT Inhibitor Domvanalimab with Imfinzi
Background and Current Status of the PACIFIC-8 Trial
AstraZeneca (AZN) is leading the PACIFIC-8 (NCT05211895) clinical trial, a global Phase 3 study for patients with Stage III unresectable non-small cell lung cancer (NSCLC). It compares Imfinzi (active ingredient: durvalumab), the standard treatment, alone, with a combination therapy of Domvanalimab, a TIGIT inhibitor developed by Arcus (RCUS) and Gilead (GILD). The trial is enrolling patients with disease that has not progressed after chemoradiotherapy (cCRT), aiming to overcome the high recurrence rate observed with Imfinzi alone.
Synergistic Mechanism of PD-L1 and TIGIT Blockade
This combination therapy targets two distinct immune checkpoint pathways that prevent immune cells from attacking cancer cells. Imfinzi inhibits the PD-L1 protein on cancer cells, restoring T-cell immune function, while Domvanalimab binds to TIGIT on T cells, preventing the suppression of immune cell activity. Notably, Domvanalimab is designed with an Fc-Silent structure that blocks Fc receptor binding to reduce side effects, representing a significant technological advantage. The simultaneous blockade of these two pathways is expected to reverse the immunosuppressive state within the tumor microenvironment and enhance anti-cancer effects.
Unmet Needs and Competition for Next-Generation Standard of Care
Currently, the market for unresectable Stage III NSCLC is dominated by Imfinzi maintenance therapy, but long-term survival rates remain low, necessitating improved treatments. Global pharmaceutical giants such as Roche, with tiragolumab, and MSD, with vibostolimab, are also actively pursuing Phase 3 trials of their own TIGIT pipelines to gain market share. Roche's SKYSCRAPER-03 trial is evaluating combination efficacy, leading to intense competition as AstraZeneca seeks to defend its market position and Arcus aims for new market entry.
Clinical Failure Risk and Investor Perspective
Recently, in April 2026, Arcus and Gilead shocked the market by halting the Phase 3 STAR-121 trial of Domvanalimab in advanced NSCLC due to insufficient efficacy. However, the PACIFIC-8 trial, directly led by AstraZeneca, is progressing smoothly without interruption, raising hopes for differentiated results. In 2025, Imfinzi recorded annual sales of $6.06 billion, and the success of this trial is crucial for defending its market dominance and potentially unlocking up to $500 million in milestone payments and royalties for Arcus, which could restore its corporate value.
The Phase 3 PACIFIC-8 trial is a pivotal study aimed at maintaining AstraZeneca's Imfinzi market share, which generated $6.06 billion in annual sales in 2025, and securing a leading position in the next generation of immune checkpoint therapies. It directly competes with Roche's SKYSCRAPER-03 trial, and given that the overall non-small cell lung cancer market is estimated at $22 billion to $25 billion in 2025, the success of this trial will be a major turning point in determining market dominance. In April 2026, Arcus's Phase 3 trial of Domvanalimab in advanced non-small cell lung cancer, STAR-121, was halted due to insufficient efficacy, making this study the final key to determining the clinical viability of TIGIT-targeted antibodies. From a researcher's perspective, the study is significant for elucidating the anti-tumor immune synergy of PD-L1 and TIGIT dual blockade, potentially establishing new criteria for overcoming resistance. In the short term, industry professionals and institutional investors are focused on the potential for Gilead to recover the $725 million in partnership rights, including the $500 million milestone payment upon U.S. approval.
Source: ClinicalTrials.gov (api_ct)