Starting Durvalumab with Chemoradiotherapy in Unresectable Stage III NSCLC Did Not Improve Outcomes: PACIFIC-2 Recalibrates the Timing of Immunotherapy

Highlight

• In PACIFIC-2, initiating durvalumab at the start of definitive concurrent platinum-based chemoradiotherapy (cCRT) for unresectable stage III non–small cell lung cancer (NSCLC) did not improve progression-free survival (PFS) or overall survival (OS) versus placebo.

• Confirmed objective response rates were identical between arms (≈61%); rates of any pneumonitis were similar, but treatment discontinuations and fatal adverse events were numerically higher with upfront durvalumab.

• The established benefit of consolidation durvalumab after completion of cCRT (the original PACIFIC strategy) remains the standard of care.

Background

Locally advanced, unresectable stage III non–small cell lung cancer presents a therapeutic challenge: combined modality therapy using platinum-based concurrent chemoradiotherapy (cCRT) has been the backbone of curative-intent treatment, but relapse risk remains high. The PACIFIC trial (Antonia et al., NEJM 2017) changed practice by showing that consolidation durvalumab given after completion of cCRT significantly improved PFS and OS compared with placebo, establishing PD-L1 blockade as standard therapy in this setting.

Biologic and translational studies suggest synergy between radiotherapy and immune checkpoint inhibitors (ICIs): radiotherapy can increase tumor antigen presentation and enhance T-cell infiltration, potentially priming an effective antitumor immune response. On that rationale, initiating PD-L1 blockade earlier—concurrently with chemoradiation—might boost immune-mediated tumor clearance and improve outcomes compared with deferring ICI until after cCRT. PACIFIC-2 tested this hypothesis in a randomized, double-blind phase III trial.

Study design

PACIFIC-2 (Bradley et al., JCO 2025) was a randomized (2:1), double-blind, placebo-controlled, phase III study evaluating whether durvalumab started from the first day of definitive platinum-based cCRT improves outcomes in patients with unresectable stage III NSCLC.

Key design elements:

• Population: Patients with unresectable stage III NSCLC eligible for definitive cCRT (328 patients randomly assigned: durvalumab n = 219; placebo n = 109).
• Intervention and comparator: Durvalumab or matching placebo initiated concurrently with cCRT and continued as consolidation (those without progression after cCRT remained on the assigned study drug until progression).
• Primary endpoint: Progression-free survival (PFS) by blinded independent central review.
• Key secondary endpoints: Objective response rate (ORR), overall survival (OS), proportion of patients alive at 24 months (OS24), and safety.

Key findings

Primary outcome—PFS: PACIFIC-2 did not meet its primary endpoint. PFS did not differ significantly between arms: hazard ratio (HR) 0.85 (95% CI, 0.65 to 1.12); P = .247. The point estimate favored durvalumab numerically but was not statistically significant.

Overall survival

OS was similar between groups: HR 1.03 (95% CI, 0.78 to 1.39); P = .823. The proportion alive at 24 months (OS24) was 58.4% with durvalumab versus 59.5% with placebo, showing no survival advantage for initiating durvalumab concurrently with cCRT.

Objective response rate and disease control

Confirmed ORR was essentially identical: 60.7% with durvalumab versus 60.6% with placebo (difference 0.2%; 95% CI, −15.2 to 16.3%; P = .976). These concordant response rates indicate that early PD-L1 blockade did not increase the proportion of patients achieving tumor shrinkage compared with cCRT alone followed by placebo consolidation.

Safety

Safety signals were notable and clinically relevant. Maximum grade 3–4 adverse events occurred in 53.4% of patients who received durvalumab versus 59.3% for placebo. The composite term pneumonitis or radiation pneumonitis was reported in 28.8% of patients in the durvalumab arm (grade ≥3: 4.6%) versus 28.7% in the placebo arm (grade ≥3: 5.6%), indicating no clear excess of clinically severe pneumonitis with concurrent durvalumab in this dataset.

However, adverse events leading to discontinuation of the investigational product were more frequent with durvalumab (25.6%) than with placebo (12.0%). Fatal adverse events were also numerically higher with durvalumab (13.7% vs 10.2%). These findings raise concerns about tolerability when durvalumab is started concurrently with cCRT and suggest that enhanced toxicity and treatment discontinuations may blunt any potential efficacy advantage.

Interpretation of the numeric trends

The hazard ratio for PFS (0.85) trended toward benefit but was imprecise and not statistically significant; OS showed no trend favoring upfront durvalumab. Identical ORRs imply that tumor shrinkage during the initial treatment period was not improved by concurrent PD-L1 blockade. Taken together, the efficacy and safety data indicate that simultaneous administration of durvalumab with cCRT does not provide a clinically meaningful advantage over cCRT plus placebo (with consolidation per initial randomization).

Expert commentary and contextualization

PACIFIC-2 provides important and somewhat unexpected guidance on the optimal sequencing of PD-L1 blockade in unresectable stage III NSCLC. The negative result underscores that biological plausibility does not always translate into improved clinical outcomes when treatment interactions, patient tolerability, and complex multimodality schedules are considered.

Potential explanations for the negative result

• Treatment interruptions and cumulative toxicity: Initiating immunotherapy during cCRT may increase treatment-related toxicity, promoting interruptions or early discontinuation of radiotherapy, chemotherapy, or the ICI itself. The higher discontinuation rate with durvalumab in PACIFIC-2 could have reduced delivered dose intensity and negated potential immune-priming benefits.
• Timing and immune contexture: Chemotherapy given concurrently can be immunosuppressive, depleting effector cells necessary for an effective response to checkpoint blockade. Radiation can be immunostimulatory but also causes transient lymphopenia; the net immune milieu during cCRT may be less permissive to checkpoint inhibition than the post-cCRT period.
• Heterogeneity in treatment regimens and patient selection: Variation in chemotherapy backbone, radiotherapy dose and technique, and baseline PD-L1 expression may influence outcomes. Subgroup analyses (exploratory) are necessary to assess whether any patient subsets derived benefit, but the overall negative result limits broad adoption of this approach.
• Statistical power and effect size: PACIFIC-2 randomized 328 patients. If the true effect of concurrent durvalumab is modest, the study may have been underpowered to detect it; however, the lack of even a consistent efficacy trend and the safety signals argue against a clinically meaningful missed benefit.

How PACIFIC-2 contrasts with PACIFIC

The original PACIFIC trial showed substantial PFS and OS benefits when durvalumab was given as consolidation after completion of cCRT, with an acceptable safety profile; this formed the current standard of care. PACIFIC-2 addressed whether shifting durvalumab earlier yields further gains; it did not. The divergence between the two trials highlights the critical importance of sequencing and timing when integrating immunotherapy with radiotherapy and chemotherapy.

Guideline and practice implications

Given the lack of efficacy and the safety signals in PACIFIC-2, consolidation durvalumab after completion of definitive cCRT remains the evidence-based standard of care for eligible patients with unresectable stage III NSCLC. Clinicians should not routinely start durvalumab concurrently with cCRT outside of a clinical trial setting.

Study limitations and unanswered questions

• Subgroup data and biomarkers: The primary report provides overall results; detailed subgroup analyses by PD-L1 expression, tumor histology, smoking status, radiation dose/fields, and chemotherapy regimen are necessary to explore heterogeneity of treatment effect. These analyses are at best exploratory and should be interpreted cautiously.
• Translational correlates: Correlative immune monitoring (peripheral and tumor-based) would be informative to understand why concurrent blockade failed to improve outcomes; publicly reported translational data are needed.
• Generalizability: Trial eligibility criteria and the mix of international centers affect applicability to real-world populations, including older patients, those with comorbidities, and patients treated with varying radiotherapy techniques.

Conclusions and clinical takeaways

PACIFIC-2 is a rigorously conducted randomized phase III trial that tested an important clinical hypothesis about sequencing immunotherapy with cCRT in unresectable stage III NSCLC. The key conclusions are:

• Starting durvalumab concurrently with definitive platinum-based cCRT did not improve PFS or OS compared with placebo, and objective response rates were unchanged.
• Rates of any pneumonitis were similar between arms, but adverse-event–related discontinuations and fatal events were numerically higher with upfront durvalumab.
• Consolidation durvalumab after completion of cCRT remains the standard of care; concurrent administration with cCRT should not be adopted in routine practice outside of clinical studies.

Future research should focus on biomarker-driven strategies, optimized sequencing, and interventions to mitigate toxicity—particularly to preserve treatment intensity during the curative-intent period. Translational studies to define the immune contexture during and after cCRT will help tailor integration of ICIs with local therapy.

Funding and clinicaltrials.gov

Funding and trial registration details are reported in the primary publication (Bradley et al., J Clin Oncol 2025). Readers should consult the original article for sponsor and registry identifiers.

References

1) Bradley JD, Sugawara S, Lee KH, et al; PACIFIC-2 Investigators. Simultaneous Durvalumab and Platinum-Based Chemoradiotherapy in Unresectable Stage III Non-Small Cell Lung Cancer: The Phase III PACIFIC-2 Study. J Clin Oncol. 2025 Nov 20;43(33):3610-3621. doi: 10.1200/JCO-25-00036 IF: 41.9 Q1 B1.

2) Antonia SJ, Villegas A, Daniel D, et al. Durvalumab after Chemoradiotherapy in Stage III Non–Small-Cell Lung Cancer. N Engl J Med. 2017;377(20):1919-1929.