Oncology · Medical Literature
[Articles] Addition of irinotecan to chemoradiotherapy as preoperative treatment for locally advanced rectal cancer (ARISTOTLE): a multicentre, open-label, phase 3, randomised controlled trial
Abstract
For MRI-defined, high-risk, locally advanced rectal cancer, the addition of irinotecan to standard of care did not improve outcomes and should not be used in combination with radiotherapy plus capecitabine.
Clinical relevance
In patients with MRI-defined, high-risk, locally advanced rectal cancer threatening or involving resection margins, does the addition of irinotecan to standard preoperative chemoradiotherapy (radiotherapy plus capecitabine) improve disease-free survival compared with standard chemoradiotherapy alone? __SNAPSHOT__ {"studyDesign":"Multicentre, open-label, parallel-design, phase 3, randomised controlled trial","setting":"75 UK hospital sites treating patients with rectal cancer","sampleSize":"n=564 in modified intention-to-treat population (standard-of-care [capecitabine-CRT]: n=284; irinotecan [IrCRT]: n=280); 589 originally randomised","population":"Adults aged ≥18 years with MRI-defined locally advanced rectal cancer threatening or involving resection margins, without distant metastases; 66% male, median age 61 years (IQR 54–68); mrT3: ~77–79%; mrT4: ~15–16%; mrCRM involved: ~49%; margin threatened ≤1mm: ~38%; ethnicity data not collected","intervention":"Preoperative radiotherapy 45 Gy in 25 daily fractions plus capecitabine 650 mg/m² twice daily on weekdays with intravenous irinotecan 60 mg/m² once weekly in weeks 1–4 (IrCRT)","comparator":"Preoperative radiotherapy 45 Gy in 25 daily fractions plus oral capecitabine 900 mg/m² twice daily on weekdays (standard CRT)","primaryOutcome":"Disease-free survival (DFS)","followUp":"Median follow-up 78 months (95% CI 75–86)","fundingSource":"Cancer Research UK (non-profit/government)"}
Key findings
Primary outcome — DFS: 36-month DFS was 68% (95% CI 63–73) in the irinotecan group versus 67% (95% CI 61–72) in the standard-of-care group; no statistically significant difference was demonstrated. From mature conference data (median follow-up 62.1 months), the DFS hazard ratio was 0.87 (95% CI 0.64–1.18; p=0.37), and overall survival HR was 0.91 (95% CI 0.63–1.30; p=0.59). Pathological complete response (pCR) rate was 20% (IrCRT) vs. 18% (CRT) (p=0.52). R0 resection rate was 90% vs. 89% (p=0.75). Locoregional failure-free survival HR was 0.94 (95% CI 0.46–1.90; p=0.86); distant metastasis-free survival HR was 0.89 (95% CI 0.63–1.25; p=0.51). Deaths occurred in 88 (31%) patients in the irinotecan group and 92 (32%) in the standard-of-care group. Treatment compliance was significantly worse in the irinotecan arm: only 75% received the full 45 Gy radiotherapy dose vs. 89% in the control arm, and only 68% received ≥90% of planned capecitabine vs. 89% in controls. Grade ≥3 adverse events were markedly more frequent with irinotecan (78% vs. 52%), including diarrhoea (14% vs. 4%), neutropenia (10% vs. 1%), and lymphocyte count decrease (66% vs. 35%). Five protocol-related deaths occurred: three in the irinotecan group (two thromboembolic events, one multiorgan failure/sepsis) and two in the standard-of-care group (one cardiac arrest, one febrile neutropenia). NNT for any outcome benefit: not calculable given no significant difference detected. NNH for grade ≥3 toxicity (calculated): approximately 4 patients treated with IrCRT to cause one additional grade ≥3 adverse event compared with standard CRT.
Practice implications
This well-powered phase 3 RCT conducted across 75 UK centres provides robust, negative evidence: the addition of irinotecan to long-course capecitabine-based chemoradiotherapy does not improve DFS, OS, pCR, R0 resection rates, or locoregional control in MRI-defined high-risk locally advanced rectal cancer. These findings are clinically important not only because benefit was absent, but because irinotecan caused substantially greater toxicity, worse compliance with both radiotherapy and capecitabine, and three treatment-related deaths in the experimental arm. The findings are directly applicable to the studied population: MRI-staged high-risk LARC (threatened or involved CRM) without metastases managed with long-course neoadjuvant CRT followed by surgery. Patients who may not be fully represented include those receiving total neoadjuvant therapy (TNT) regimens, short-course radiotherapy, non-UK practice settings, and non-white ethnic groups (ethnicity data not collected). The results do not support irinotecan intensification in this setting and effectively close this question for unselected patients. A concurrent post-hoc biomarker analysis (eBioMedicine, 2026) suggests possible heterogeneity of treatment effect by AI-derived tumour cell density (TCD), with TCD-high patients showing potential DFS and OS benefit; however, this is hypothesis-generating only and does not alter clinical practice at this time. Only the abstract of the primary Lancet Oncology publication was available for this summary; full-text data (including subgroup analyses, quality of life, surgical morbidity details, and complete OS curves) were not independently reviewable. __LIMITATIONS__ Open-label design introduces potential performance and assessment bias, although the primary endpoint (DFS) is relatively objective.,Significantly lower treatment compliance in the irinotecan arm (lower RT and capecitabine completion rates) may have confounded the efficacy assessment, making it difficult to distinguish lack of efficacy from inadequate dose delivery.,Ethnicity data were not collected, limiting assessment of generalisability across diverse populations.,The trial was conducted exclusively at UK sites, and results may not generalise to settings where total neoadjuvant therapy (TNT), short-course radiotherapy, or different surgical standards are used.,The trial predates widespread adoption of TNT approaches and immunotherapy in rectal cancer, limiting contemporary contextual relevance.,Surrogate endpoints such as pCR were not validated as surrogates for long-term survival in this trial's specific population.,This summary is based on abstract-level data only; full statistical tables, subgroup analyses, quality-of-life data, and complete survival curves were not available for review.,Post-hoc biomarker analyses (TCD by AI) reported in a companion paper are hypothesis-generating and subject to multiple comparisons, selection bias, and lack of prospective validation. __BOTTOM_LINE_CATEGORY__ practice_changing __BOTTOM_LINE__ The ARISTOTLE trial definitively demonstrates that adding irinotecan to standard capecitabine-based long-course chemoradiotherapy does not improve disease-free or overall survival in MRI-defined high-risk locally advanced rectal cancer, and confers substantially greater toxicity and worse treatment compliance. Irinotecan should not be used in combination with radiotherapy and capecitabine in this setting outside of a clinical trial. Biomarker-driven patient selection (e.g., AI-derived tumour cell density) is hypothesis-generating and requires prospective validation before influencing practice.