The Lancet Oncology DECEMBER 07, 2020

Short-course radiotherapy followed by chemotherapy before total mesorectal excision (TME) versus preoperative chemoradiotherapy, TME, and optional adjuvant chemotherapy in locally advanced rectal cancer (RAPIDO): a randomised, open-label, phase 3 trial

Bahadoer RR, Dijkstra EA, van Etten B, et al. (RAPIDO collaborative investigators)

Bottom Line

In high-risk locally advanced rectal cancer, total neoadjuvant therapy comprising short-course radiotherapy and consolidation chemotherapy before surgery significantly reduced disease-related treatment failure and doubled the pathological complete response rate compared to standard chemoradiotherapy.

Key Findings

1. Disease-related treatment failure (DrTF) at 3 years was significantly reduced in the total neoadjuvant therapy (TNT) arm (23.7%) compared to the standard-of-care arm (30.4%) (HR 0.75, 95% CI 0.60-0.95; p=0.019).

2. The 3-year cumulative probability of distant metastases was significantly lower in the TNT arm (20.0%) versus the standard-of-care arm (26.8%) (HR 0.69; p=0.0048).

3. The pathological complete response (pCR) rate was essentially doubled in the TNT arm (28.0%) compared to the standard chemoradiotherapy arm (14.3%) (OR 2.37; p<0.0001).

4. There was no significant difference in 3-year overall survival between the TNT and standard care groups (89.1% vs. 88.8%; HR 0.92, p=0.59).

5. Serious adverse events occurred in 38% of patients in the experimental group and 34% of patients in the standard-of-care group, without significant differences in surgical complication rates.

Study Design

Design

RCT

Open-Label

Sample

920

Patients

Duration

4.6 yr

Median

Setting

Multicenter, 7 countries

Population Adults with newly diagnosed, MRI-defined high-risk locally advanced rectal cancer (featuring at least one of: cT4a/b, cN2, extramural vascular invasion, involved/threatened mesorectal fascia, or enlarged lateral lymph nodes).

Intervention Total neoadjuvant therapy (TNT): short-course radiotherapy (5x5 Gy) followed by consolidation systemic chemotherapy (6 cycles of CAPOX or 9 cycles of FOLFOX4), then total mesorectal excision (TME).

Comparator Standard of care: preoperative long-course chemoradiotherapy (capecitabine + 50.4 Gy) followed by TME, and optional postoperative adjuvant chemotherapy (8 cycles of CAPOX or 12 cycles of FOLFOX4).

Outcome Disease-related treatment failure (DrTF) at 3 years, defined as the first occurrence of locoregional failure, distant metastasis, a new primary colorectal tumor, or treatment-related death.

Study Limitations

• The trial was open-label, which inherently carries a risk of performance and detection biases, although the primary endpoints were relatively objective.

• Adjuvant chemotherapy was optional in the standard-of-care arm (and administered to only ~58% of eligible patients). While this accurately reflects real-world postoperative compliance challenges, it makes it difficult to ascertain whether the TNT arm's superior outcomes were due to the neoadjuvant timing of chemotherapy or simply improved overall exposure to systemic therapy.

• The study was not originally powered to detect differences in overall survival.

• Although the 3-year results showed comparable local control, a subsequent 5-year follow-up update published in 2023 revealed a higher rate of locoregional recurrence in the experimental TNT arm (10% vs. 6%, p=0.027), highlighting a potential weakness of short-course radiotherapy for controlling bulky local disease compared to long-course chemoradiation.

Clinical Significance

The RAPIDO trial was a paradigm-shifting study that solidified Total Neoadjuvant Therapy (TNT) as a frontline standard of care for high-risk locally advanced rectal cancer. By moving systemic chemotherapy to the preoperative setting, the trial solved the longstanding issue of poor postoperative chemotherapy compliance, translating into a meaningful reduction in distant micrometastatic failure. Furthermore, doubling the pathological complete response rate (from 14% to 28%) generated tremendous enthusiasm for organ-preservation ('watch-and-wait') strategies, potentially allowing a substantial proportion of patients to safely avoid radical surgery and permanent colostomies. However, clinicians now carefully weigh the risk of locoregional recurrence when deciding between short-course and long-course radiation backbones for TNT.

Historical Context

For decades, the undisputed standard of care for locally advanced rectal cancer was preoperative long-course chemoradiotherapy followed by total mesorectal excision (TME) and postoperative adjuvant chemotherapy. However, survival plateaued because distant metastases remained the primary driver of mortality, and fewer than half of patients successfully completed postoperative chemotherapy due to surgical complications or slow recovery. The concept of Total Neoadjuvant Therapy (TNT)—front-loading both radiotherapy and chemotherapy before surgery—emerged to tackle these early micrometastases and guarantee systemic treatment delivery. Published contemporaneously with the PRODIGE 23 trial, RAPIDO provided definitive Phase 3 evidence that TNT significantly improves disease outcomes and tumor downstaging.

Guided Discussion

High-yield insights from every perspective

Med Student

Medical Student

What is the pathophysiological and anatomical rationale for moving systemic chemotherapy into the neoadjuvant setting (Total Neoadjuvant Therapy) for locally advanced rectal cancer, as seen in the RAPIDO trial, compared to the traditional postoperative adjuvant approach?

Key Response

Students must understand that locally advanced rectal cancer carries a high risk of systemic micrometastases. Moving chemotherapy to the neoadjuvant setting addresses distant micrometastatic disease earlier, utilizes an intact tumor vasculature for better drug delivery before surgical disruption, and avoids delays in systemic therapy that often occur due to postoperative complications, thereby driving the doubled pathological complete response (pCR) rates seen in the study.

Resident

The RAPIDO trial demonstrated a doubling of the pathological complete response (pCR) rate. How might you use the concept of pCR to counsel a patient regarding the 'Watch and Wait' non-operative management strategy, and what specific clinical criteria are required to consider this approach safely?

Key Response

Residents must link trial endpoints to real-world clinical decisions. The increased pCR with TNT opens the door for organ preservation (Watch and Wait), which spares the patient the morbidity of a Total Mesorectal Excision (e.g., permanent colostomy, sexual or urinary dysfunction). Safely implementing this requires a clinical complete response (cCR) validated by rigorous restaging with high-resolution MRI, endoscopy, and digital rectal exam.

Fellow

While the initial RAPIDO trial showed a significant reduction in disease-related treatment failure, subsequent updates raised concerns about a potential increase in locoregional recurrence in the experimental arm. How do you weigh the trade-off between improved systemic control and potential risks of local failure when selecting short-course TNT versus long-course chemoradiation for a borderline resectable patient with an involved mesorectal fascia?

Key Response

Fellows should be aware of mature data and trial nuances. The lack of immediate tumor shrinkage after short-course RT (before chemo) might affect margin clearance differently than standard long-course CRT. Balancing these risks is crucial; for tumors with heavily involved margins, some centers prefer long-course CRT to ensure maximum local downstaging, whereas short-course TNT is preferred to mitigate high distant metastatic risk.

Attending

The RAPIDO trial allowed for 'optional' adjuvant chemotherapy in the standard control arm, which mirrors real-world compliance issues where many patients fail to complete postoperative therapy. How do you address the critique that the TNT arm's success was largely driven by guaranteed delivery of systemic therapy, and how does this practical reality shape your multidisciplinary tumor board recommendations?

Key Response

Attendings deal with system issues and patient compliance. Adjuvant chemo compliance is historically poor (often around 50%). TNT guarantees systemic therapy delivery upfront while the patient is most fit. The teaching point is that TNT is functionally a highly effective strategy to ensure treatment compliance, but it requires careful patient selection to ensure they can tolerate intense upfront, sequential modalities without experiencing severe toxicity that might delay definitive surgery.

Scholarly Review

Critical appraisal through the lens of expert reviewers and guideline development

PhD

The RAPIDO trial utilizes 'disease-related treatment failure' (DrTF) as its primary endpoint rather than standard overall survival (OS) or disease-free survival (DFS). From a methodological perspective, what are the statistical advantages and potential biases introduced by using this specific composite endpoint in a phase 3 oncology trial?

Key Response

DrTF is a composite encompassing local failure, distant metastasis, new primary colorectal tumor, or treatment-related death. Methodologically, it increases the event rate, thereby reducing the necessary sample size and required follow-up time (a statistical and financial advantage). However, composite endpoints risk diluting the impact of critical, hard endpoints like OS with softer events, potentially overstating the clinical benefit if the components do not carry equal clinical weight.

Journal Editor

As an editor evaluating this open-label trial, how does the lack of blinding, combined with the discretionary nature of adjuvant chemotherapy in the control arm (where only about 47% received it), threaten the internal validity of the trial's conclusions regarding the true biological superiority of the TNT regimen?

Key Response

Editors must spot structural biases. The open-label design and optional adjuvant chemo in the control arm create a massive asymmetry in systemic therapy exposure. A rigorous reviewer would flag that the trial effectively compares guaranteed neoadjuvant chemo against highly variable, poorly-complied-with adjuvant chemo, making it a pragmatic trial of 'treatment timing and guaranteed compliance' rather than definitively proving the biological superiority of the exact drugs and radiation sequencing.

Guideline Committee

Based on the RAPIDO trial's demonstration of doubled pCR rates and reduced DrTF, alongside similar findings from the PRODIGE 23 trial, how should current NCCN and ESMO guidelines stratify the recommendation for Total Neoadjuvant Therapy versus standard chemoradiotherapy, and should TNT be universally recommended for all locally advanced rectal cancers?

Key Response

Guideline committees must synthesize evidence to define the standard of care with precision. Because RAPIDO specifically targeted 'high-risk' locally advanced rectal cancer (e.g., cT4, extramural vascular invasion, involved mesorectal fascia), the guideline recommendation should elevate TNT to a preferred, Category 1 level but specifically restrict it to high-risk subsets defined by high-quality MRI. Current NCCN guidelines reflect this by making TNT a preferred approach, emphasizing MRI risk-stratification to prevent overtreatment of intermediate-risk patients.

Clinical Landscape

Noteworthy Related Trials

2004

German Rectal Cancer Trial CAO/ARO/AIO-94

n = 823 · NEJM

Tested

Preoperative chemoradiotherapy followed by TME

Population

Patients with clinically staged T3, T4, or node-positive rectal cancer

Comparator

Postoperative chemoradiotherapy

Endpoint

Overall survival

Key result: Preoperative chemoradiotherapy significantly reduced local recurrence (6% vs 13% at 5 years) and improved sphincter preservation rates compared to postoperative treatment.

2020

PRODIGE 23

n = 461 · Lancet Oncol

Tested

Neoadjuvant mFOLFIRINOX followed by chemoradiotherapy and TME

Population

Patients with locally advanced rectal cancer

Comparator

Standard preoperative chemoradiotherapy and TME

Endpoint

3-year disease-free survival

Key result: Neoadjuvant mFOLFIRINOX significantly improved 3-year disease-free survival (76% vs 69%) and metastasis-free survival compared to standard care.

2022

OPRA Trial

n = 324 · J Clin Oncol

Tested

Chemoradiotherapy followed by consolidation chemotherapy

Population

Patients with stage II or III rectal cancer

Comparator

Induction chemotherapy followed by chemoradiotherapy

Endpoint

Disease-free survival and organ preservation rate

Key result: Both TNT sequencing approaches yielded similar disease-free survival, but the consolidation chemotherapy sequence resulted in significantly higher rates of organ preservation (53% vs 43%).

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