tivunatamig (SSGJ-707) first-line NSCLC Phase 2 update: mPFS of 13.6/13.8 months looks impressive, but there is no HR and the control arms have only 30–40 patients each

Data as of 2026-10-29 (Taipei time). [Fact] statements are sourced; [Inference] statements are this article's judgment.

1. One-line conclusion

[Fact] At ESMO (European Society for Medical Oncology) 2026, poster 2660P, 3SBio updated Chinese Phase 2 data for tivunatamig (PF-08634404/SSGJ-707, a PD-1 [programmed cell death protein 1] × VEGF [vascular endothelial growth factor] bispecific antibody) plus chemotherapy as first-line treatment for advanced NSCLC (non-small cell lung cancer): per the press release, mPFS (median progression-free survival) was 13.6 vs 8.3 months in squamous and 13.8 vs 9.7 months in non-squamous disease, with tislelizumab + chemotherapy as the comparator (PR Newswire).

[Inference] The direction matches ivonescimab's HARMONi-6, but this is an open-label, dose-finding Phase 2 with ORR (objective response rate) as the primary endpoint, and the press release gives no PFS HR (hazard ratio) or confidence interval; "longest mPFS in class" is a cross-trial comparison and cannot serve as evidence of superiority over competitors.

For sponsors: at least two PD-1×VEGF bispecifics have now shown a PFS signal against tislelizumab + chemotherapy in first-line NSCLC in China; a newcomer that wants to differentiate needs to win OS (overall survival) in a global Phase 3 against pembrolizumab + chemotherapy, not to compare Phase 2 mPFS figures.

2. What happened

[Fact] The trial is an open-label, multicenter, randomized Phase 2 (NCT06412471) whose registered primary endpoints are ORR and safety (ClinicalTrials.gov). Part 1 (non-squamous) tested 5/10/20 mg/kg or tislelizumab with carboplatin + pemetrexed; Part 2 (squamous) began with dose finding, then compared the selected 10 mg/kg dose with tislelizumab, each with carboplatin + paclitaxel, plus a nab-paclitaxel arm (SITC 2025 abstract). A total of 261 patients were enrolled (122 non-squamous, 139 squamous); 50% were ≥65 years, 80% had a smoking history, and more than 40% had PD-L1 (programmed death-ligand 1) TPS (tumor proportion score) <1% (PR Newswire). On the difference in numbers: ClinicalTrials.gov lists an "estimated" enrollment of 235, status Unknown, last updated 2024-07-30, with estimated primary completion 2025-07 (NCT06412471), meaning the registry stopped being updated before enrollment finished; at the SITC 2025 cutoff 244 patients had been enrolled (119 non-squamous, 125 squamous) (SITC 2025 abstract), and ESMO 2026 reports 261 (PR Newswire). We could not find a public explanation for actual enrollment exceeding the registry estimate.

[Fact] Data cutoff 2026-08-06. Evaluable patients and cORR (confirmed ORR): non-squamous, tivunatamig 77.5% in 40 vs tislelizumab 44.7% in 38; squamous, tivunatamig + paclitaxel 80.7% in 57 and + nab-paclitaxel 69.2% in 13 vs tislelizumab 67.7% in 31 (PR Newswire). Of 126 patients with detectable baseline ctDNA (circulating tumor DNA) and paired samples, 61.9% cleared it by C3D1 (about week 9); mPFS was 16.4 months in those who cleared vs 9.6 months in those who did not (PR Newswire). Safety: grade ≥3 TRAEs (treatment-related adverse events) were "broadly comparable" with the tislelizumab arm, with no new grade 5 TRAEs since SITC; no percentages were disclosed this time (PR Newswire).

[Fact] At the previous SITC (Society for Immunotherapy of Cancer) 2025 (cutoff 2025-07-04): grade ≥3 TRAEs 39.0% in the 10 mg/kg arm vs 32.8% with tislelizumab; 3 (2.9%) treatment-related deaths in the 10 mg/kg arm, 2 from hemoptysis and 1 of unknown cause (SITC 2025 abstract, JITC open access). Per-arm bleeding and hemoptysis rates appear only in the poster PDF on Pfizer's website, which was blocked by the site's protection this round and could not be publicly verified, so this article does not cite them.

For sponsors: bleeding and hemoptysis with PD-1×VEGF bispecifics in squamous NSCLC are a focus of regulatory review; "no new grade 5 events" in Phase 2 does not mean the risk is ruled out, and Phase 3 should prespecify bleeding-risk exclusion criteria and monitoring.

3. Why it succeeded

[Inference] Mechanism: blocking PD-1 and VEGF together can in theory improve the tumor microenvironment and strengthen the immune response (PR Newswire). The cORR gap was larger in non-squamous (77.5% vs 44.7%) than in squamous disease (80.7% vs 67.7%), consistent with the squamous control arm's own high response rate (PR Newswire).

[Inference] Endpoints and statistics: first, there is no PFS HR or confidence interval, and the control arms had only 38 and 31 evaluable patients (PR Newswire), so mPFS point estimates are very unstable at this sample size; we could not find whether PFS was assessed by independent central review. Second, the squamous control-arm mPFS of 8.3 months is higher than the 6.90 months for the same comparator (tislelizumab + chemotherapy) in the HARMONi-6 Phase 3 (Summit/SEC), showing that the Phase 2 population differs from Phase 3, so cross-trial mPFS comparisons do not hold. Third, the longer mPFS in ctDNA clearers comes from grouping by on-treatment response, a "responders vs non-responders" comparison with time-related bias; it cannot serve as evidence of drug effect, nor show superiority over competitors. Fourth, "longest mPFS in class" is the company's own claim, not head-to-head (PR Newswire).

[Inference] A usable Phase 3 anchor: ivonescimab's HARMONi-6 in squamous NSCLC vs tislelizumab + chemotherapy gave mPFS 11.14 vs 6.90 months, HR 0.60 (0.46–0.78) (Summit/SEC); tivunatamig's press-release squamous figures of 13.6 vs 8.3 months point the same way, but the size of the gap cannot be compared.

For sponsors: when citing the tivunatamig Phase 2, say only that it is "directionally consistent with HARMONi-6"; when setting Phase 3 effect sizes, assume an HR no better than 0.60 (the HARMONi-6 PFS HR, Summit/SEC), i.e. an effect no larger than HARMONi-6's, rather than extrapolating from Phase 2 mPFS.

4. Regulatory and commercial implications

[Fact] In 2025 3SBio licensed global development and commercialization rights to SSGJ-707 to Pfizer in a deal worth more than US$6 billion in total, including a US$1.4 billion upfront payment and a US$100 million equity investment; the company says 11 international clinical trials have been registered (PR Newswire). Pfizer's global Phase 3 Symbiotic-Lung-01 (NCT07222566) is double-blind and randomized against pembrolizumab + chemotherapy, split by histology into squamous and non-squamous parts, with estimated enrollment of 1,410 and dual primary endpoints of OS and BICR (blinded independent central review) PFS; the registry's estimated primary completion is 2029-02-27 (ClinicalTrials.gov). The 148TiP (trial in progress) design abstract published in ESMO Open lists separate numbers for each part, but neither that page nor its DOI would open this round and it could not be publicly verified, so this article does not cite it.

[Inference] On the regulatory side, a single-country Chinese Phase 2 cannot support FDA (US Food and Drug Administration) or EMA (European Medicines Agency) approval; Symbiotic-Lung-01 has OS as a dual primary endpoint against pembrolizumab, which signals that Pfizer expects regulators to require survival data, not just PFS. As for the NMPA (National Medical Products Administration, China), we could not find whether 3SBio has a separate Chinese Phase 3 or filing plan.

For sponsors: the global first-line NSCLC PD-1×VEGF Phase 3 for tivunatamig will not read out until at least 2029 (ClinicalTrials.gov); sponsors starting similar trials before then can still use pembrolizumab + chemotherapy as the comparator, but should build in clauses for competitor Phase 3 results rewriting the landscape.

5. Recommendations for the next trial and OncoLattice

[Inference] First, sponsors in this class should size the randomized control in Phase 2 large enough to estimate an HR (at least so that the confidence interval is meaningful) and have PFS assessed by independent central review; otherwise the data carry limited value in BD (business development) and regulatory discussions. Second, in the squamous population, prespecify exclusion criteria such as hemoptysis, cavitation and tumor abutting major blood vessels, because at SITC 2 of the 3 treatment-related deaths in the 10 mg/kg arm were from hemoptysis (SITC 2025 abstract); we could not find the individual risk features of those deaths. Third, early ctDNA clearance can be used for stratification or as an exploratory endpoint, but landmark analysis is needed to handle time-related bias. Fourth, OncoLattice site strategy: Symbiotic-Lung-01 plans to enroll 1,410 patients (ClinicalTrials.gov); if other PD-1×VEGF bispecifics also open first-line NSCLC trials at the same sites, competition for patients will be intense, so prioritize sites not yet saturated with similar trials (the number of similar trials per site needs a separate inventory, which we did not do).

For OncoLattice: first-line NSCLC PD-1×VEGF trials will compete for the same patients at the same sites; site assessment should first inventory how many similar trials each site already has.

6. Open questions and what to watch

Event	Expected timing	Specific source
PFS HR, confidence interval, PFS assessment method, this round's grade ≥3 TRAE percentages	Shown on ESMO 2026 poster 2660P (2026-10-26 12:00–12:45 CET); full publication timing not disclosed	3SBio's Chinese announcement lists the poster number and slot (3SBio); the press release does not give these figures (PR Newswire)
Phase 2 OS	Not disclosed; the registry page was last updated 2024-07-30, and its estimated completion date of 2025-08 has passed	Registry page NCT06412471; 3SBio's press release does not mention OS (PR Newswire)
Symbiotic-Lung-01 primary analysis (OS and BICR PFS)	Registry estimates primary completion 2029-02-27 and study completion 2032-08-26	Registry page NCT07222566
Chinese Phase 3 or NMPA filing	Not disclosed	3SBio's announcement says only that multiple global pivotal Phase III studies are under way, with no Chinese filing listed (3SBio)

For sponsors: until the poster's HR and confidence interval are in hand, do not use 13.6/13.8 months as the basis for any effect-size assumption.

The next thing to watch is Symbiotic-Lung-01's OS: it is tivunatamig's first test in a global, double-blind setting against pembrolizumab.

Evidence limitations

ESMO 2026 data here come from 3SBio's English press release (PR Newswire) and Chinese announcement (3SBio); the trial design and SITC 2025 safety come from the JITC open-access abstract (SITC 2025 abstract); registry data come from ClinicalTrials.gov (NCT06412471, NCT07222566); HARMONi-6 figures come from Summit's press release filed with the SEC (Summit/SEC). We did not obtain the ESMO 2026 poster 2660P file; the SITC poster PDF and the ESMO Open 148TiP page would not open this round, and the related figures have been removed.

Advice for readers: the press release gives no PFS HR (PR Newswire); if the poster's HR confidence interval crosses 1 at its upper bound, or PFS was not assessed by independent central review, this article's conclusion of "directionally consistent with HARMONi-6" should be downgraded to "a difference in ORR only".

Note: differences from the original relay

mPFS of 13.6 vs 8.3 months in squamous and 13.8 vs 9.7 months in non-squamous disease, and mPFS of 16.4 months in ctDNA clearers, match the press release (PR Newswire). Addition: the press release was issued at 08:34 US Eastern on 10/28, i.e. 20:34 Taipei time on 10/28; 3SBio's Chinese announcement says the poster was shown on 2026-10-26 (3SBio). The PFS HR could not be found.