Chemoradiotherapy versus short-course radiotherapy for response-adapted organ preservation in early-stage and intermediate-stage rectal cancer (STAR-TREC): 12-month results of an international, multicentre, open-label, parallel-group, randomised, phase 2/3 trial

BACKGROUND: Total mesorectal excision (TME) is the standard treatment for most early-stage and intermediate-stage rectal cancer but can cause substantial perioperative morbidity, functional impairment, and reduced quality of life. We assessed whether long-course chemoradiotherapy (LCCRT) or short-course radiotherapy (SCRT) could increase organ preservation and reduce surgery, toxicity, and quality-of-life harms without compromising oncological outcomes. METHODS: twice daily), SCRT-based organ preservation (SCRT-OP; 25 Gy in five fractions), or primary TME. Phase 2 assessed feasibility, with recruitment at months 12 and 24 as the primary endpoint and feasibility thresholds of four or more and six or more randomisations per month, respectively. Phase 3 adopted a partially randomised patient-preference design, allowing participants to choose either organ preservation or TME. Participants that chose organ preservation were randomly assigned (1:1) to receive LCCRT-OP or SCRT-OP using centralised, computer-generated assignment, with stratification by country and MRI T category (≤T3a vs T3b) using minimisation. The phase 3 primary endpoint was organ-preservation 30 months after treatment initiation, defined as absence of TME, stoma, or local recurrence, which was assessed in the modified intention-to-treat population, which included participants in phase 2 and phase 3. After a planned interim analysis of unmasked phase 2 data, the trial steering committee and independent data monitoring committee recommended reporting a 12-month, modified intention-to-treat analysis of implementation outcomes for participants recruited before Aug 8, 2023. This study is registered with ISRCTN (14240288) and is closed. FINDINGS: Between June 14, 2017, and April 8, 2024, 503 participants were enrolled at 37 sites. Phase 2 enrolled 120 participants, with recruitment rates of three and six participants per month at months 12 and 24, respectively. Overall, 12-month TME-free survival was 60% (47 of 78 participants). After phase 3 recruitment ended, interim analysis of unmasked phase 2 data showed an early TME-free survival benefit with LCCRT versus SCRT (12-month median TME-free survival not reached [95% CI not reached-not reached] vs 7·6 months [95% CI 6·4-not reached]; hazard ratio [HR] 3·7 [95% CI 1·7-8·0]; posterior probability of superiority >99·5%). The trial steering committee and independent data monitoring committee therefore recommended expanded analysis of 426 participants recruited before Aug 8, 2023: 120 from phase 2 and 306 from phase 3. 17 participants withdrew before treatment, leaving 409 in the modified intention-to-treat population: 163 allocated to LCCRT, 168 to SCRT, and 78 to primary TME. 116 (28%) participants were female and 293 (72%) were male. Among participants who opted for organ preservation, 12-month TME-free survival was 78·5% (95% CI 72·4-85·1) with LCCRT and 60·6% (53·6-68·4) with SCRT (HR 1·90 [95% CI 1·29-2·81]). The most common grade 3-4 serious adverse events were gastrointestinal disorders (four [2%] with LCCRT vs six [4%] with SCRT vs six [8%] with TME) and procedural complications (three [2%] with LCCRT vs five [3%] with SCRT vs five [6%] with TME). One participant allocated to primary TME died after an anastomotic leak. INTERPRETATION: These early results support a response-adapted organ-preservation approach, with LCCRT appearing more effective than SCRT at 12 months. Organ-preservation might also reduce treatment-related toxicity compared with primary TME. Longer follow-up is needed for the prespecified 30-month endpoint and definitive functional and oncological outcomes.