UNION NCT04928807
ForcT3-4 or N+ rectal adenocarcinoma ≤10 cm from anal verge
TL;DR3-yr EFS 91.3% vs 77.4%, HR 0.33 (0.15-0.71), P=0.0029: SCRT → camrelizumab + CAPOX vs long-course CRT → CAPOX in LARC.
The control is long-course CRT, so the EFS gain (HR 0.33) comes with a switch to 25 Gy/5f. That makes SCRT the RT backbone for an IO-containing TNT, not a compromise. Because RT schedule and camrelizumab were changed together, the trial cannot say whether SCRT itself is what lets IO work in largely pMMR disease.
In cT3-4 or node-positive low/mid rectal adenocarcinoma, this supports SCRT followed by PD-1 inhibitor plus CAPOX as an evidence-backed TNT option. It does not settle IO use when no PD-1 agent equivalent to camrelizumab is available, or questions of organ preservation.
The experimental arm swapped 50.4 Gy/28f chemoRT for 25 Gy/5f and still improved 3-yr EFS (91.3% vs 77.4%). That puts SCRT forward as the RT platform for IO consolidation. Whether SCRT is synergistic or just interchangeable cannot be separated from the camrelizumab effect.
Adding camrelizumab across neoadjuvant and adjuvant CAPOX (up to 17 cycles) gave EFS HR 0.33 with G≥3 TRAE 51.3% vs 48.2%. It is a signal for PD-1 blockade beyond dMMR in LARC, though the MMR breakdown and OS are not in source, and camrelizumab availability outside China limits how far it transfers.
8 details 2 trials watching
Phase 3, randomized 1:1, N=231 (113 vs 118), accrued July 2021 to March 2023. Median follow-up 36.8 vs 35.6 mo at the October 1, 2025 cutoff.
cT3-4 or N+ rectal adenocarcinoma, tumor ≤10 cm from the anal verge. MMR/MSI composition of the enrolled cohort is not reported in source.
Experimental: SCRT 25 Gy/5f. Control: 50.4 Gy/28f with concurrent capecitabine 825 mg/m2 BID. Target volumes are not reported in source.
Both arms: 2 neoadjuvant + 6 adjuvant cycles of CAPOX. Experimental adds camrelizumab 200 mg d1 given alongside CAPOX for up to 17 cycles.
Primary: BIRC-assessed pCR rate (result not in source). Key secondary endpoints with prespecified α: investigator-assessed EFS and OS.
G≥3 TRAE over the whole treatment period 51.3% (59/115) vs 48.2% (54/112). The RT-attributable split is not reported.
RAPIDO set SCRT followed by consolidation chemo as a TNT option, and PRODIGE 23 did the same for an LCCRT-based approach. UNION is the first phase 3 to layer a PD-1 inhibitor onto SCRT in LARC, building on earlier SCRT + IO phase 2 signals such as TORCH.
The safety population (115 vs 112) does not match randomization (113 vs 118), so some pts received the other arm's treatment. Neoadjuvant CAPOX was only 2 cycles in the control arm, lighter than full TNT backbones. OS and surgical or organ-preservation outcomes are absent.
The EFS effect is large and was tested under alpha control, but it comes from a two-variable comparison. It supports the whole package and does not establish what SCRT or camrelizumab contributes individually.
| Endpoint | SCRT + camrelizumab + CAPOX | LCCRT + CAPOX | Effect |
|---|---|---|---|
| 3-yr EFS (investigator) | 91.3% (83.9-95.4) | 77.4% (67.9-84.4) | HR 0.33 (0.15-0.71), P=0.0029 |
| G≥3 TRAE | 51.3% (59/115) | 48.2% (54/112) | n/a |
| Median f/u | 36.8 mo (34.8-37.8) | 35.6 mo (34.3-36.9) | n/a |
CONSORT flow
Randomized phase 3, but the primary pCR result is not in source and EFS is secondary. SCRT and camrelizumab change together, so the benefit cannot be attributed to either.
- Does SCRT, versus long-course CRT, drive the immunotherapy benefit?
- Unreported pCR primary result and OS
- Benefit in confirmed pMMR/MSS pts specifically recruiting Neoadjuvant CAPOX With or Without Pucotenlimab Plus Selective Radiotherapy for Locally Advanced Rectal Cancer Phase 3n=556 · primary completion 2032-04 · phase 3 CAPOX ± pucotenlimab, pMMR/MSS LARCn=612 · primary completion 2032-12 · phase 3 SCRT+PD-1 iTNT vs LCRT TNT, MSS/pMMR only
📚 Sources · 📄 1 paper
Abstract
The longer read
UNION is a package trial. The experimental arm differs from control in two ways at once: the radiation schedule moves from 50.4 Gy in 28 fractions with capecitabine to 25 Gy in 5, and a PD-1 inhibitor is added through the neoadjuvant and adjuvant phases. An EFS hazard ratio of 0.33 therefore tells the reader that the combined strategy beats long-course chemoradiation followed by CAPOX. It does not tell them whether short-course RT is the better partner for immunotherapy, whether camrelizumab would deliver the same gain after long-course CRT, or whether the schedule change is neutral and IO does all the work. The biological rationale for pairing hypofractionated RT with PD-1 blockade (immunogenic cell death, less lymphodepletion from a short course) is exactly what this design cannot test. A factorial or a third arm would have been needed.
The second issue is hierarchy. The registered primary endpoint was BIRC-assessed pCR, and the presented abstract does not give that result. EFS is a key secondary with its own alpha allocation, so the P=0.0029 is not a post-hoc finding. Still, a reader is entitled to see the primary before accepting the authors' new-standard claim, especially since pCR is the endpoint most directly tied to the immunotherapy hypothesis.
The magnitude is also striking for a trial of 231 pts. The confidence interval on the HR (0.15-0.71) is wide, and the 3-yr EFS estimates have overlapping intervals at their edges. A control arm at 77.4% is within the plausible range for this population, but the experimental arm's 91.3% sits high enough that replication in a non-Chinese population, with a PD-1 agent available elsewhere, matters before generalizing. The MMR/MSI composition of the cohort is not given. If any dMMR pts were included and were unevenly distributed, they could carry a disproportionate share of the IO effect.
Against RAPIDO and PRODIGE 23, UNION is better read as an IO extension of the SCRT-based TNT lineage than as a replacement of it: the control arm's neoadjuvant chemotherapy was only two CAPOX cycles, lighter than the consolidation those trials established. A modern full-TNT comparator might narrow the gap. Toxicity looks acceptable on the reported G≥3 TRAE rates, but the mismatch between randomized and safety denominators suggests crossover or as-treated reassignment, which should be clarified in the full report. Organ preservation, surgical morbidity and OS will decide whether this becomes practice. For a radiation oncologist, the actionable point today is that 25 Gy/5f held up as the RT component of an intensified, IO-containing curative regimen.