Bristol Myers Squibb (NYSE: BMY) has reported positive topline results from the planned interim analysis of Phase 3 ACTION-1, confirming that RayzeBio’s investigational actinium-225 radiopharmaceutical RYZ101 significantly improved progression-free survival in patients with advanced gastroenteropancreatic neuroendocrine tumors (GEP-NETs) previously treated with lutetium-177-based therapy. Announced on October 12, 2026, the study met its prespecified primary endpoint through blinded independent central review, marking a significant clinical milestone for targeted alpha radiopharmaceutical therapy.
The randomized trial compared RYZ101, also known as actinium-225 DOTATATE, against investigator-selected standard-of-care treatments in patients whose somatostatin receptor-positive tumors had progressed following earlier lutetium-177 radiopharmaceutical treatment. Bristol Myers Squibb described the improvement as statistically significant and clinically meaningful, with safety findings consistent with the investigational medicine’s known profile. However, the company has not yet disclosed the progression-free survival hazard ratio, median progression-free survival, confidence intervals or detailed adverse-event results.
The findings are particularly consequential because ACTION-1 examines a difficult treatment setting rather than the initial use of radiopharmaceuticals in neuroendocrine cancer. Lutetium-177 DOTATATE, marketed by Novartis as Lutathera, has established an important role in treating somatostatin receptor-positive GEP-NETs, but patients can eventually experience disease progression despite treatment. RYZ101 uses a different radioactive isotope to deliver highly concentrated radiation to receptor-expressing tumor cells, creating the possibility of another targeted treatment after progression on an established radiopharmaceutical.
For Bristol Myers Squibb, the result provides clinical support for the radiopharmaceutical strategy behind its approximately $4.1 billion acquisition of RayzeBio in February 2024. The company plans to engage with the United States Food and Drug Administration about a potential regulatory submission, while continuing to monitor participants for overall survival. The next evidence milestone will be the detailed ACTION-1 results, which must establish the magnitude and durability of benefit alongside a sufficiently characterized safety profile.
What did the Phase 3 ACTION-1 interim analysis establish about RYZ101’s efficacy?
ACTION-1, registered as NCT05477576, is a global, randomized, controlled, open-label Phase 1b/3 programme evaluating RYZ101 in patients with inoperable, advanced, well-differentiated GEP-NETs. The Phase 3 portion compares the investigational radiopharmaceutical with physician-selected standard-of-care options, including higher-dose or more frequent long-acting somatostatin analogues, everolimus and sunitinib. The trial registry’s October 2026 update identifies 343 enrolled participants across the programme, although the announcement does not specify how many patients contributed to the interim efficacy analysis.
The primary endpoint is progression-free survival assessed through blinded independent central review, an important design feature because the treating investigators and patients know which treatment is being administered. Independent review reduces the potential for treatment knowledge to influence interpretation of tumor imaging. Progression-free survival measures the period before disease progression or death, providing information about disease control without automatically demonstrating that patients live longer.
Bristol Myers Squibb confirmed that the planned interim analysis crossed the statistical threshold for the primary endpoint. This is stronger evidence than an uncontrolled observation of tumor shrinkage, particularly because patients were randomized against active treatment choices relevant to the post-lutetium setting. Nevertheless, the magnitude of the effect remains unknown because the company did not disclose the hazard ratio, median survival figures or detailed subgroup outcomes.
Those missing numbers are important for clinicians assessing the clinical value of treatment. A statistically significant result can represent different magnitudes of benefit depending on the absolute difference in progression-free survival, the duration of follow-up and the characteristics of the enrolled population. The eventual presentation will also need to clarify how outcomes varied across gastrointestinal and pancreatic tumor origins and whether the reported benefit was consistent across the standard-of-care comparator options.
The company has confirmed that patients will continue receiving care according to the study protocol and that overall survival follow-up is ongoing. No overall survival advantage has been established by the October announcement, and the findings should not be interpreted as proof that RYZ101 extends life expectancy. Its demonstrated achievement, based on the company’s topline disclosure, is improvement in the trial’s primary progression-free survival endpoint.
How does RYZ101’s actinium-225 mechanism differ from Lutathera’s lutetium-177 therapy?
RYZ101 is designed to deliver an alpha-emitting radioactive isotope directly to cancer cells expressing somatostatin receptor subtype 2, a molecular target commonly found in well-differentiated neuroendocrine tumors. The treatment combines actinium-225 with DOTATATE, a somatostatin receptor-binding molecule that helps concentrate the radioactive payload in receptor-positive tumor tissue. After binding and internalization, the isotope delivers radiation capable of causing complex DNA damage, including double-strand breaks that may be difficult for cancer cells to repair.
The distinction from Lutathera lies primarily in the type of radiation delivered. Lutathera uses lutetium-177, a beta-emitting isotope, while RYZ101 employs actinium-225, which emits alpha particles with higher linear energy transfer and a substantially shorter tissue range. These physical properties provide a rationale for investigating whether alpha radiation can produce meaningful antitumor effects in cancers that have progressed after beta-emitting radiopharmaceutical treatment.
However, greater radiation potency does not automatically translate into better clinical outcomes or a superior safety profile. The distribution of radioactive material within tumors, receptor expression, absorbed radiation doses and exposure to normal organs can all affect efficacy and toxicity. Alpha-emitting therapies also present distinct dosimetry considerations, meaning the ability to deliver concentrated radiation must be evaluated alongside potential harm to surrounding tissues.
ACTION-1 does not directly compare RYZ101 with retreatment using lutetium-177 DOTATATE. Instead, it investigates RYZ101 after disease progression following prior lutetium-based therapy, against selected non-radiopharmaceutical standard treatments. The positive result therefore supports the potential clinical activity of actinium-225 DOTATATE in this setting without establishing that it is inherently superior to lutetium-177 radiopharmaceuticals.
Why could RYZ101 address an important treatment gap after progression on lutetium-177?
Gastroenteropancreatic neuroendocrine tumors originate in neuroendocrine cells within the gastrointestinal tract or pancreas and can follow substantially different clinical courses depending on their grade, location and extent of disease. Many well-differentiated tumors grow relatively slowly, but metastatic or unresectable disease may require several successive treatment approaches over time. Long-acting somatostatin analogues, molecularly targeted medicines, chemotherapy and peptide receptor radionuclide therapy are among the available options for selected patients.
Lutathera received its original United States approval for adults with somatostatin receptor-positive GEP-NETs in January 2018, with the indication expanded to patients aged 12 years and older in April 2024. Its introduction established receptor-targeted radiation as an approved treatment approach for these tumors. Nevertheless, disease progression after peptide receptor radionuclide therapy remains a challenging clinical situation, particularly when patients have already received several systemic treatments.
The ACTION-1 population was selected to address this unmet need. The study focuses on well-differentiated, somatostatin receptor-positive GEP-NETs with documented progression following prior lutetium-177-labelled somatostatin analogue treatment. The trial’s design also requires measurable receptor-avid disease and adequate organ function, meaning its results should not automatically be generalized to patients with receptor-negative tumors or substantially different disease characteristics.
The investigation is especially relevant because treatment decisions after previous radiopharmaceutical therapy can depend on tumor biology, earlier drug exposure, disease location and remaining organ reserve. By comparing RYZ101 against active treatment choices, the study provides a framework for assessing whether another receptor-targeted radiation approach offers additional disease control. Its regulatory and clinical implications will become clearer once the full efficacy and safety findings are available.
What did the earlier 17-patient RYZ101 study reveal about tumor responses and safety?
The Phase 3 result builds on a smaller Phase 1b investigation that established the dose used in the subsequent randomized trial. Updated findings presented at the 2025 American Society of Clinical Oncology Gastrointestinal Cancers Symposium involved 17 patients with advanced GEP-NETs previously treated with lutetium-177-based therapy. All participants received RYZ101, with 15 completing four treatment cycles and two receiving two cycles.
The investigators reported a confirmed objective response rate of 29.4%, representing five of the 17 patients at the December 2023 data cutoff. This included one complete response and four partial responses, while seven additional patients had stable disease. The findings suggested antitumor activity in a previously treated population, but the absence of a randomized comparator and small sample size limited conclusions about relative efficacy.
The safety findings require equally careful interpretation. Treatment-emergent anemia and nausea each occurred in 58.8% of participants, while fatigue was reported in 52.9%. Nine patients experienced Grade 3 or higher treatment-emergent adverse events, including five with events classified as treatment-related, although none of the six serious adverse events was considered treatment-related by investigators.
The analysis also reported one fatal event involving hepatic failure, which investigators assessed as unrelated to the study drug. No adverse events resulted in permanent treatment discontinuation, but four patients required treatment modification, interruption or delay. These findings demonstrate why the absence of treatment-related serious adverse events should not be interpreted as an absence of important treatment-related toxicity.
The dose selected for Phase 3 was 10.2 megabecquerels administered intravenously every eight weeks for four treatment cycles. Patients in the experimental arm also receive amino acid infusions for renal protection, reflecting the importance of managing radiation exposure to the kidneys. The larger ACTION-1 safety dataset will be necessary to establish how frequently clinically significant hematologic, renal and other toxicities occur under the selected regimen.
How does the Phase 3 success strengthen Bristol Myers Squibb’s $4.1 billion RayzeBio acquisition?
Bristol Myers Squibb completed its acquisition of RayzeBio on February 26, 2024, acquiring a clinical-stage radiopharmaceutical business for approximately $4.1 billion in total consideration. The transaction brought RYZ101 into its oncology development portfolio alongside research programmes directed at additional tumor targets. It also provided specialized manufacturing and isotope-related capabilities that are important for developing radioactive medicines.
The acquisition represented a deliberate expansion beyond Bristol Myers Squibb’s established oncology strengths in immunotherapy and conventional targeted medicines. RayzeBio’s platform uses radioactive payloads linked to molecules that recognize specific tumor-associated targets, creating opportunities to investigate radiopharmaceutical treatment across different solid cancers. RYZ101 was the most advanced programme when the acquisition was completed, making its Phase 3 progress particularly relevant to assessing the clinical value of the transaction.
The October 2026 result provides evidence that the lead programme has achieved a meaningful development milestone, but it does not establish a financial return on the acquisition. Regulatory approval, market access, manufacturing costs, clinical adoption and the size of the eligible patient population will determine its eventual commercial contribution. The opportunity may also be constrained by the relatively specialized population of patients progressing after earlier lutetium-177 therapy.
Bristol Myers Squibb has not disclosed a revenue forecast or anticipated launch date for RYZ101 in connection with the interim findings. Reuters reported on October 12 that analysts viewed the outcome as supportive of the company’s radiopharmaceutical strategy, although some remained cautious about the commercial opportunity amid emerging competitors. The differing interpretations reflect the gap between a successful clinical endpoint and the economics of bringing a specialized cancer treatment to market.
RYZ101 is also being investigated in earlier-stage research involving hormone receptor-positive metastatic breast cancer, while RayzeBio’s broader platform includes programmes directed at other tumor-associated targets. A successful GEP-NET development programme could provide operational and scientific experience relevant to future radiopharmaceutical research, but it would not independently establish efficacy in other cancer types.
Can RayzeBio’s expanding manufacturing network support commercial actinium-225 treatment?
Radiopharmaceutical manufacturing presents requirements that differ substantially from those associated with conventional medicines. Radioactive isotopes must be produced, combined with targeting molecules, tested and delivered within defined periods while maintaining product quality and radiation safety. Their physical decay introduces additional timing requirements, making manufacturing location, supply reliability and distribution capabilities important components of commercial readiness.
Bristol Myers Squibb has already invested in a 77,000-square-foot radiopharmaceutical manufacturing facility in Indianapolis, Indiana, which became operational for clinical production in 2025. The facility supports isotope-related operations and manufacturing of investigational radiopharmaceuticals, including RYZ101. The company has described its distribution capability as enabling treatment doses to reach clinical sites within approximately three days following release from production.
A further expansion was announced in August 2026, when Indiana authorities disclosed RayzeBio’s plans to invest more than $173 million in a new manufacturing facility in Whitestown. The proposed development involves approximately 225,000 square feet of additional infrastructure and is expected to create up to 100 jobs across the company’s regional operations by the end of 2029. The project is planned rather than completed, and its future capacity should not be confused with manufacturing resources already available.
The additional investment highlights how commercial radiopharmaceutical development depends on industrial execution as well as clinical evidence. Actinium-225 availability, manufacturing consistency, radiochemical quality control, specialized transport and the readiness of nuclear medicine treatment centres will all influence the practical reach of an approved product. Bristol Myers Squibb’s existing clinical manufacturing capability reduces some development uncertainty, although commercial-scale availability remains dependent on further operational and regulatory requirements.
What must the FDA evaluate before RYZ101 can become an approved GEP-NET treatment?
The FDA granted RYZ101 Orphan Drug Designation for GEP-NETs in August 2026, recognizing the programme’s development within a rare disease population. The designation can provide certain development incentives, including potential eligibility for orphan-drug market exclusivity following approval, but it does not establish efficacy or represent marketing authorization. RYZ101 remains investigational despite the positive Phase 3 announcement.
Bristol Myers Squibb now intends to engage with the FDA to determine the next steps toward a regulatory submission. The planned discussions will need to address the full clinical evidence package, including the interim efficacy analysis, safety information, statistical analysis and manufacturing readiness. The company has not yet confirmed a submission date or announced that an application has been accepted for review.
One critical question will be the strength of the progression-free survival benefit. The FDA will be able to evaluate the magnitude and consistency of the treatment effect alongside its clinical relevance in the post-lutetium population. Overall survival follow-up, adverse-event characterization and the completeness of the trial data will also inform the benefit-risk assessment.
Long-term safety deserves particular attention because patients may have received substantial radiation exposure during earlier radiopharmaceutical treatment. The cumulative effects on bone marrow and kidneys, along with the possibility of delayed complications, require careful evaluation. The October announcement’s description of a consistent safety profile is encouraging but cannot replace detailed adverse-event rates and longer follow-up.
RayzeBio Chief Medical Officer Amreen Husain has characterized the results as an important development for patients whose disease has progressed after lutetium-based treatment. ACTION-1 principal investigator Simron Singh of Sunnybrook Health Sciences Centre and the University of Toronto has also emphasized the longstanding uncertainty surrounding optimal treatment after earlier radiopharmaceutical therapy. Their assessments reflect the significance of obtaining randomized Phase 3 evidence in this setting, although the complete results remain necessary to determine how RYZ101 should fit into clinical practice.
What do the ACTION-1 results mean for the future of targeted alpha radiopharmaceutical therapy?
ACTION-1 represents an important test of whether the physical advantages of alpha-emitting isotopes can translate into clinically meaningful outcomes in a randomized late-stage cancer trial. RayzeBio describes the findings as the first results from a Phase 3 study of an actinium-225-based targeted radiopharmaceutical therapy in any indication. The result provides encouraging evidence for the approach, while the extent of benefit and its applicability to other tumors remain unresolved.
The next major milestone will be the disclosure of the complete efficacy and safety data at a future medical meeting. Clinicians will need to examine the hazard ratio, absolute progression-free survival difference, subgroup outcomes and detailed tolerability findings to assess the treatment’s value for eligible patients. Continued overall survival monitoring will provide additional information about the durability and consequences of disease control.
For Bristol Myers Squibb, the outcome strengthens the clinical foundation of its radiopharmaceutical investment at a time when oncology companies are developing new ways to deliver targeted radiation. Its existing Indianapolis manufacturing operation and planned Whitestown expansion demonstrate that the company is building infrastructure alongside its clinical pipeline. However, commercial success will ultimately depend on authorization, safe and reliable supply, appropriate patient selection and access through specialist treatment centres.
RYZ101 has achieved a significant milestone by meeting the primary endpoint of a randomized Phase 3 study in patients with advanced GEP-NETs following lutetium-177 treatment. The finding creates a potential new option in a difficult treatment setting without yet establishing an overall survival benefit, regulatory approval or broad clinical superiority. The full ACTION-1 dataset and forthcoming FDA discussions will determine whether this first major late-stage success for RayzeBio’s actinium-225 platform can progress into an authorized cancer treatment.
