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Importance The definition of cure in stage II to III colon cancer (CC) remains unclear due to limitations in conventional end points, which include deaths and second primary tumors as events. These can complicate communication with patients regarding long-term outcomes. Objective To distinguish relapses from competing health-related events to classify long-term outcomes years after surgery and explore when the incidence of true relapses of the initial CC approaches 0% to define cure in this disease. Design, Setting, and Participants This pooled analysis of individual patient–level data from 15 phase 3 randomized clinical trials assessed time to CC-related relapse using Kaplan-Meier and Aalen-Johansen methods, with death and second primary tumors treated as competing risks. Cox regression models evaluated prognostic associations, stratified by sex, stage, and tumor. Patients with stage II to III CC who underwent adjuvant chemotherapy were included. All patients had undergone radical surgery for CC and received adjuvant chemotherapy with a median follow-up of at least 6 years. The Adjuvant Colon Cancer Endpoints (ACCENT) and the International Duration Evaluation of Adjuvant Chemotherapy (IDEA) databases included adjuvant studies conducted between 1996 and 2015. Data were analyzed from February 2022 to June 2025. Exposures Adjuvant chemotherapy regimens varied across trials, including fluoropyrimidines alone or in combination with oxaliplatin or biologic agents. Main Outcomes and Measures The primary outcome was time to CC-related recurrence. The predefined threshold for cure was a recurrence risk below 0.5%. Results Of 35 213 included patients, 19 346 (54.9%) were male, and the mean (SD) age was 60.2 (10.8) years. The incidence rate of recurrence peaked at 6.4% (1993 of 31 373) between month 6 and month 12 and decreased continuously until year 10 of follow-up never exceeding 0.5%. Recurrence rate appeared to increase again after year 10 and peaked at 2.0% during year 12.5 to year 13, a pattern observed exclusively in the MOSAIC trial. Competing-event analysis revealed that death and second primary tumors inflated the apparent recurrence rate, especially for older patients. The overall cumulative incidence of relapse with death as competing risk was lower among female patients (hazard ratio, 0.58; 95% CI, 0.45-0.76; P < .001). Conclusions and Relevance In this pooled analysis of phase 3 randomized clinical trials, a recurrence rate less than 0.5% occurred after 6 years from surgery, supporting a practical definition of cure. Recognizing this milestone may improve patient communication, guide follow-up duration, and reduce unnecessary long-term surveillance.

PURPOSE A number of studies suggest that older patients may have reduced or no benefit from the addition of oxaliplatin to fluoropyrimidines as adjuvant chemotherapy for stage III colon cancer (CC). MATERIALS AND METHODS We studied the prognostic impact of age, as well as treatment adherence/toxicity patterns according to age, in patients with stage III CC who received 3 or 6 months of infusional fluorouracil, leucovorin, and oxaliplatin/capecitabine and oxaliplatin (CAPOX) on the basis of data collected from trials from the ACCENT and IDEA databases. Associations between age and time to recurrence (TTR), disease-free survival (DFS), overall survival (OS), survival after recurrence (SAR), and cancer-specific survival (CSS) were assessed by a Cox model or a competing risk model, stratified by studies and adjusted for sex, performance status, T and N stage, and year of enrollment. RESULTS A total of 17,909 patients were included; 24% of patients were age older than 70 years (n = 4,340). Patients age ≥70 years had higher rates of early treatment discontinuation. Rates of grade ≥3 adverse events were similar between those older and younger than 70 years, except for diarrhea and neutropenia that were more frequent in older patients treated with CAPOX (14.2% v 11.2%; P = .01 and 12.1% v 9.6%; P = .04, respectively). In multivariable analysis, TTR was not significantly different between patients <70 years and those ≥70 years, but DFS, OS, SAR, and CSS were significantly shorter in those patients ≥70 years. CONCLUSION In patients ≥70 years with stage III CC fit enough to be enrolled in clinical trials, oxaliplatin-based adjuvant chemotherapy was well tolerated and led to similar TTR compared with younger patients, suggesting similar efficacy. TTR may be a more appropriate end point for efficacy in this patient population.

PURPOSE Oxaliplatin-based adjuvant chemotherapy in patients with stage III colon cancer (CC) for 6 months remains a standard in high-risk stage III patients. Data are lacking as to whether early discontinuation of all treatment (ETD) or early discontinuation of oxaliplatin (EOD) could worsen the prognosis. MATERIALS AND METHODS We studied the prognostic impact of ETD and EOD in patients with stage III CC from the ACCENT/IDEA databases, where patients were planned to receive 6 months of infusional fluorouracil, leucovorin, and oxaliplatin or capecitabine plus oxaliplatin. ETD was defined as discontinuation of treatment and EOD as discontinuation of oxaliplatin only before patients had received a maximum of 75% of planned cycles. Association between ETD/EOD and overall survival and disease-free survival (DFS) were assessed by Cox models adjusted for established prognostic factors. RESULTS Analysis of ETD and EOD included 10,447 (20.9% with ETD) and 7,243 (18.8% with EOD) patients, respectively. Compared with patients without ETD or EOD, patients with ETD or EOD were statistically more likely to be women, with Eastern Cooperative Oncology Group performance status ≥ 1, and for ETD, older with a lower body mass index. In multivariable analyses, ETD was associated with a decrease in disease-free survival and overall survival (hazard ratio [HR], 1.61, P < .001 and HR, 1.73, P < .001), which was not the case for EOD (HR, 1.07, P = .3 and HR, 1.13, P = .1). However, patients who received < 50% of the planned cycles of oxaliplatin had poorer outcomes. CONCLUSION In patients treated with 6 months of oxaliplatin-based chemotherapy for stage III CC, ETD was associated with poorer oncologic outcomes. However, this was not the case for EOD. These data favor discontinuing oxaliplatin while continuing fluoropyrimidine in individuals with significant neurotoxicity having received > 50% of the planned 6-month chemotherapy.

PURPOSE Early-onset (EO) colorectal cancer (CRC, age < 50 years) incidence is increasing. Decisions on optimal adjuvant therapy should consider treatment adherence, adverse events, and expected outcomes in a population with life expectancy longer than later-onset (LO) CRC (age ≥ 50 years). MATERIALS AND METHODS Individual patient data from six trials in the International Duration Evaluation of Adjuvant Chemotherapy database were analyzed. Characteristics, treatment adherence, and adverse events in stage II or III EO-CRC and LO-CRC were compared. To reduce confounders of non–cancer-related deaths because of age or comorbidities, time to recurrence (3-year relapse-free rate) and cancer-specific survival (5-year cancer-specific mortality rate) were considered. RESULTS Out of 16,349 patients, 1,564 (9.6%) had EO-CRC. Compared with LO-CRC, EO-CRC had better performance status (86% v 80%, P < .01), similar T stage (% T1-3/T4: 76/24 v 77/23, P = .97), higher N2 disease rate (24% v 22%, P < .01), more likely to complete the planned treatment duration (83.2% v 78.2%, P < .01), and received a higher treatment dose intensity, especially with 6-month regimens. Gastrointestinal toxicity was more common in EO-CRC; hematologic toxicity was more frequent in LO-CRC. Compared with LO-CRC, significantly worse cancer-specific outcomes were demonstrated especially in high-risk stage III EO-CRC: lower 3-year relapse-free rate (54% v 65%; hazard ratio [HR] 1.33; 95% CI, 1.14 to 1.55; P value < .001) and higher 5-year cancer-specific mortality rate (24% v 20%; HR 1.21; 95% CI, 1.00 to 1.47; P value < .06). In this subgroup, no difference was observed with 3 or 6 months of therapy, with equally poor disease-free survival rates (57% v 56%; HR 0.97; 95% CI, 0.73 to 1.29; P value = .85). CONCLUSION Young age is negatively prognostic in high-risk stage III CRC and associated with significantly higher relapse rate; this is despite better treatment adherence and higher administered treatment intensity, suggesting more aggressive disease biology.

3517 Background: Incidence of early-onset colorectal cancer (eoCRC, age < 50) is steadily increasing. Decisions on adjuvant treatment (adjTx) regimen and duration should consider tx adherence, toxicity (tox) and expected outcomes in a population with life-expectancy longer than late onset CRC (loCRC, age ≥ 50). Methods: Individual patient data from stage II/III patients (pts) from 6 randomised trials in the IDEA database were used to compare characteristics, tx adherence, and adverse events of eoCRC to loCRC. To reduce the confounder of non-cancer-related deaths due to age/co-morbidities, time-to-recurrence (TTR) and cancer-specific survival (CSS) were compared by stratified Gay k-sample test. 5-year cancer-specific mortality (CSM) rate were estimated by adjusted cumulative incidence function. 3-year relapse-free survival (RFS) rate were compared by stratified and adjusted COX models. Results: Out of 16,349 pts included, 1564 (9.6%) were eoCRC. Compared to loCRC, eoCRC had lower percent of male pts (51% vs 57%, p < 0.01) better performance status (PS0 86% vs 80%, p < 0.01), similar T stage distribution (% T1-3/T4: 76/24 vs 77/23, p = 0.97), higher rate of N2 disease (24% vs 22%, p < 0.01), more likely to complete pre-planned duration of adjTx (83.2% vs 78.2%, p < 0.01) and received a higher tx intensity especially with 6 month tx (mean oxaliplatin dose intensity 75% vs 72%, p < 0.01; capecitabine 85% vs 78%, p < 0.01; 5FU 85% vs 82% p < 0.01). Gastrointestinal tox was more common in eoCRC (any grade nausea 58% vs 45%, p < 0.01; any grade vomiting 22% vs 16%, p < 0.01); haematological tox was more frequent in loCRC (62% vs, 69%, p = < 0.01); any grade neuropathy rate was similar (75%). Significant interaction was found between age and T stage for TTR (p = 0.04). Clinical outcome estimates and comparisons are shown in Table. Notably, high risk stage III (T4/N2) eoCRC had significantly lower 3-y RFS rate (54% vs 64%, HRadj 0.74, p < 0.01). Conclusions: eoCRC have better tx adherence than loCRC, as expected. While in high risk stage II and low risk stage III, cancer-specific outcomes are not different, in high risk stage III young age is negatively prognostic and associated with significantly higher relapse rate and risk of CRC death; this is despite a higher administered adjTx-intensity, suggesting a more aggressive disease biology. Clinical trial information: NCT00749450 (SCOT); NCT00646607 (TOSCA); NCT01150045 (CALGB/SWOG 80702); NCT00958737 (IDEA France) [Table: see text]

PURPOSE: As oxaliplatin results in cumulative neurotoxicity, reducing treatment duration without loss of efficacy would benefit patients and healthcare providers. PATIENTS AND METHODS: Four of the six studies in the International Duration Evaluation of Adjuvant Chemotherapy (IDEA) collaboration included patients with high-risk stage II colon and rectal cancers. Patients were treated (clinician and/or patient choice) with either fluorouracil, leucovorin, and oxaliplatin (FOLFOX) or capecitabine and oxaliplatin (CAPOX) and randomly assigned to receive 3- or 6-month treatment. The primary end point is disease-free survival (DFS), and noninferiority of 3-month treatment was defined as a hazard ratio (HR) of < 1.2- v 6-month arm. To detect this with 80% power at a one-sided type one error rate of 0.10, a total of 542 DFS events were required. RESULTS: 3,273 eligible patients were randomly assigned to either 3- or 6-month treatment with 62% receiving CAPOX and 38% FOLFOX. There were 553 DFS events. Five-year DFS was 80.7% and 83.9% for 3-month and 6-month treatment, respectively (HR, 1.17; 80% CI, 1.05 to 1.31; P [for noninferiority] .39). This crossed the noninferiority limit of 1.2. As in the IDEA stage III analysis, the duration effect appeared dependent on the chemotherapy regimen although a test of interaction was negative. HR for CAPOX was 1.02 (80% CI, 0.88 to 1.17), and HR for FOLFOX was 1.41 (80% CI, 1.18 to 1.68). CONCLUSION: Although noninferiority has not been demonstrated in the overall population, the convenience, reduced toxicity, and cost of 3-month adjuvant CAPOX suggest it as a potential option for high-risk stage II colon cancer if oxaliplatin-based chemotherapy is suitable. The relative contribution of the factors used to define high-risk stage II disease needs better understanding.

Abstract Purpose: Clinical trials are expensive and lengthy, where success of a given trial depends on observing a prospectively defined number of patient events required to answer the clinical question. The point at which this analysis time occurs depends on both patient accrual and primary event rates, which typically vary throughout the trial's duration. We demonstrate real-time analysis date projections using data from a collection of six clinical trials that are part of the IDEA collaboration, an international preplanned pooling of data from six trials testing the duration of adjuvant chemotherapy in stage III colon cancer, and we additionally consider the hypothetical impact of one trial's early termination of follow-up. Patients and Methods: In the absence of outcome data from IDEA, monthly accrual rates for each of the six IDEA trials were used to project subsequent trial-specific accrual, while historical data from similar Adjuvant Colon Cancer Endpoints (ACCENT) Group trials were used to construct a parametric model for IDEA's primary endpoint, disease-free survival, under the same treatment regimen. With this information and using the planned total accrual from each IDEA trial protocol, individual patient accrual and event dates were simulated and the overall IDEA interim and final analysis times projected. Projections were then compared with actual (previously undisclosed) trial-specific event totals at a recent census time for validation. The change in projected final analysis date assuming early termination of follow-up for one IDEA trial was also calculated. Results: Trial-specific predicted event totals were close to the actual number of events per trial for the recent census date at which the number of events per trial was known, with the overall IDEA projected number of events only off by eight patients. Potential early termination of follow-up by one IDEA trial was estimated to postpone the overall IDEA final analysis date by 9 months. Conclusions: Real-time projection of the final analysis time during a trial, or the overall analysis time during a trial collaborative such as IDEA, has practical implications for trial feasibility when these projections are translated into additional time and resources required.