# Rectal Cancer: Total Neoadjuvant Therapy and Organ Preservation

## Overview

Locally advanced rectal cancer (LARC), defined as clinical stage II-III disease, is managed through a multimodality approach that integrates chemotherapy, radiation, and surgery. Over time, the treatment paradigm has shifted significantly. Initially, postoperative chemoradiotherapy (CRT) was the standard, as established by the German CAO/ARO/AIO-94 trial. This evolved into preoperative CRT, which improved local control and toxicity profiles. More recently, total neoadjuvant therapy (TNT) has emerged, consolidating all systemic therapy before surgery. This approach enhances chemotherapy compliance and increases rates of pathologic complete response (pCR). Additionally, the watch-and-wait (W&W) strategy has gained attention as an organ-preservation method for patients achieving a clinical complete response (cCR) after CRT, allowing selected patients to avoid radical surgery.

## Evolution of Treatment Paradigm

### Postoperative to Preoperative CRT

The German CAO/ARO/AIO-94 trial, published by Sauer et al. in 2004, was pivotal in establishing preoperative CRT as the standard of care for patients with cT3-4 or node-positive rectal cancer. This randomized study compared preoperative CRT (50.4 Gy combined with 5-fluorouracil) to postoperative CRT. The preoperative approach resulted in a significantly lower local recurrence rate (6% versus 13%), reduced acute and late toxicities, and a higher rate of sphincter preservation. Importantly, overall survival (OS) was similar between the two groups. These findings firmly established preoperative CRT as superior to postoperative treatment.

### Short-Course Radiotherapy

Short-course radiotherapy (RT) was investigated in the Swedish Rectal Cancer Trial in 1997, which delivered 25 Gy in 5 fractions over one week followed by surgery within a week. This regimen reduced local recurrence and improved overall survival compared to surgery alone. The Dutch TME Trial further demonstrated that short-course RT combined with total mesorectal excision (TME) decreased the 10-year local recurrence rate from 11% to 5% compared to surgery alone. Subsequent trials, including TROG 01.04, the Polish trial, and Stockholm III, showed that short-course RT provides oncologic outcomes equivalent to long-course CRT for most patients. These data support short-course RT as a valid alternative, especially in TNT protocols where surgery is delayed.

## Total Neoadjuvant Therapy (TNT)

The RAPIDO trial, a phase III study by Bahadoer et al. in 2021, compared short-course RT (5x5 Gy) followed by six cycles of CAPOX or nine cycles of FOLFOX4 chemotherapy before TME, against the standard long-course CRT (50.4 Gy with capecitabine) followed by TME and adjuvant chemotherapy. The TNT arm achieved a significantly higher pCR rate (28.4% versus 14.3%) and demonstrated a lower 3-year disease-related treatment failure rate (23.7% versus 30.4%, hazard ratio [HR] 0.75). Additionally, the TNT group had a significantly reduced 3-year distant metastasis rate, although locoregional failure was slightly higher in the TNT arm, a trend that was not statistically significant. There was no difference in overall survival at the time of initial reporting.

Similarly, the PRODIGE 23 trial led by Conroy et al. in 2021 evaluated induction chemotherapy with six cycles of FOLFIRINOX followed by CRT (50 Gy with capecitabine) and TME, compared to standard CRT followed by TME and adjuvant mFOLFOX6. The TNT arm showed a pCR rate of 27.8% versus 12.1% in the standard arm. Three-year disease-free survival (DFS) was improved at 76% compared to 69% (HR 0.69), and metastasis-free survival was superior with TNT. Although overall survival showed a trend toward improvement, it was not yet statistically significant.

The OPRA trial, a phase II randomized study by Garcia-Aguilar et al. in 2022, investigated two sequences of TNT for LARC: induction chemotherapy (FOLFOX or CAPOX) followed by CRT, versus CRT followed by consolidation chemotherapy. Patients achieving a clinical complete response were offered a watch-and-wait approach instead of surgery. The consolidation chemotherapy arm demonstrated a higher organ preservation rate at three years (53% versus 41%) and superior TME-free survival, indicating better organ preservation with CRT followed by consolidation chemotherapy. Three-year DFS was similar between the two arms, approximately 78%, and comparable to historical controls undergoing TME. This trial established the CRT-then-consolidation chemotherapy sequence as the preferred strategy for watch-and-wait protocols.

| Trial | Experimental Arm | Control Arm | pCR Rate (Exp vs. Ctrl) | Key Outcome |
|---|---|---|---|---|
| RAPIDO | 5x5 Gy → CAPOX/FOLFOX → TME | Long-course CRT → TME → adj chemo | 28.4% vs. 14.3% | Lower distant metastasis with TNT |
| PRODIGE 23 | FOLFIRINOX → CRT → TME | CRT → TME → mFOLFOX6 | 27.8% vs. 12.1% | Improved 3-yr DFS (76% vs. 69%) |
| OPRA | CRT → consolidation chemo (W&W if cCR) | Induction chemo → CRT (W&W if cCR) | — | Higher organ preservation with consolidation (53% vs. 41%) |
| German CAO/ARO/AIO-94 | Preoperative CRT | Postoperative CRT | — | Lower local recurrence (6% vs. 13%) |

## Radiation Therapy Technique

### Long-Course CRT

Long-course CRT typically involves delivering 45 to 50.4 Gy in 25 to 28 fractions, with each fraction being 1.8 Gy. A boost dose to the gross tumor volume (GTV) may increase the total dose to 50.4-54 Gy, administered either as a simultaneous integrated boost (SIB) or sequentially. Concurrent chemotherapy usually consists of capecitabine at 825 mg/m² twice daily on radiation days or continuous infusion 5-FU at 225 mg/m² per day. Target volumes include the GTV, which encompasses the rectal tumor and involved mesorectal or pelvic lymph nodes identified on CT, MRI, or PET-CT. The clinical target volume (CTV) covers the entire mesorectum, presacral space, and at-risk nodal stations. Internal iliac nodes are always included, obturator nodes are included for most LARC cases, and external iliac nodes are included if the tumor involves the anterior rectal wall or adjacent organs, such as in T4b tumors invading the bladder, prostate, or vagina. Inguinal nodes are only included for very distal tumors involving the anal canal or perianal skin. The planning target volume (PTV) is generated by adding a 5-10 mm margin around the CTV.

### Short-Course RT

Short-course RT delivers 25 Gy in 5 fractions of 5 Gy each over one week, targeting the same CTV as long-course CRT, including the mesorectum and nodal stations. No concurrent chemotherapy is given. Traditionally, surgery follows within one week of radiation. However, in TNT protocols, surgery is delayed 12 to 16 weeks to allow for consolidation chemotherapy. The Stockholm III trial demonstrated that delaying surgery by 4 to 8 weeks after short-course RT improves tumor downstaging without increasing surgical complications.

### IMRT/VMAT

Intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) are increasingly standard for rectal cancer radiation. These techniques reduce acute gastrointestinal toxicities such as diarrhea and nausea, as well as genitourinary toxicity, compared to three-dimensional conformal radiation therapy (3D-CRT). Bone marrow-sparing IMRT is particularly important as it reduces hematologic toxicity during CRT, which enhances chemotherapy compliance and reduces treatment interruptions. Dose constraints include limiting femoral head exposure to V30 less than 50% to reduce the risk of avascular necrosis, and small bowel constraints of V45 less than 195 cc and V35 less than 300 cc.

## Watch-and-Wait (Organ Preservation)

### Patient Selection

The watch-and-wait approach is reserved for patients who achieve a clinical complete response after neoadjuvant therapy. Criteria for cCR include the absence of any residual mass on digital rectal examination (DRE), the presence of a white scar or flat ulcer on endoscopy, no residual tumor on MRI characterized by mrTRG 1 (magnetic resonance tumor regression grade), and negative biopsies if performed. Patients with a near-complete response may exhibit small residual mucosal abnormalities that could regress further with continued observation. Assessment is optimally performed 8 to 12 weeks after completing CRT or TNT to avoid premature evaluation.

### Surveillance Protocol

Patients managed with watch-and-wait undergo intensive surveillance. DRE and endoscopy are performed every 1 to 3 months during the first two years, then every six months thereafter. Pelvic MRI is obtained every 3 to 6 months for the first three years. Systemic surveillance includes CT scans of the chest, abdomen, and pelvis every six months, alongside monitoring of carcinoembryonic antigen (CEA) levels.

### Outcomes

Data from the International Watch & Wait Database (IWWD), which includes 880 patients managed non-operatively after cCR, reveal a 2-year local regrowth rate of 25.2%. Despite this, the 5-year overall survival is 85%, and disease-specific survival is 94%. Importantly, over 95% of local regrowths are salvageable with surgery. The rate of distant metastasis is comparable to patients undergoing TME after achieving a pathologic complete response. It is crucial to understand that local regrowth in this context is not equivalent to local recurrence; most regrowths are intraluminal and amenable to salvage TME without compromising oncologic outcomes.

### Challenges

Defining cCR remains subjective and challenging, as no single diagnostic modality is perfectly sensitive. There is a risk of understaging, particularly in patients with near-cCR who may harbor viable tumor cells in mesorectal lymph nodes. Long-term outcomes beyond five years are limited, and patient anxiety along with compliance to intensive surveillance protocols can be problematic. Consequently, watch-and-wait is not yet considered standard of care universally and is best pursued in experienced centers or within clinical trials.

<image>A flowchart showing the evolution of rectal cancer treatment paradigms. Starting from postoperative CRT (German trial, 2004) to preoperative CRT (standard since 2004) to total neoadjuvant therapy (RAPIDO 2021, PRODIGE 23 2021) to organ preservation with watch-and-wait (OPRA 2022). At each transition point, the key trial name and result driving the paradigm shift is annotated. The TNT pathway branches into two arms at the bottom: surgery (TME) for non-responders and watch-and-wait for clinical complete responders.</image>

<image>A multi-panel endoscopic and MRI image set showing the assessment of clinical complete response. Panel A: baseline endoscopy showing a circumferential rectal mass at 5 cm from the anal verge. Panel B: post-TNT endoscopy showing a flat white scar with no residual mass (cCR). Panel C: baseline pelvic MRI (sagittal T2-weighted) showing a T3N1 tumor. Panel D: post-TNT MRI showing a dark signal void scar at the tumor site with no residual intermediate signal (mrTRG 1). Annotations highlight the features of cCR.</image>

<image>An axial CT planning image showing an IMRT/VMAT dose distribution for rectal cancer. The CTV (red) encompasses the mesorectum, presacral space, and bilateral internal iliac and obturator nodes. The 95% isodose line (green) conformally covers the CTV. Key organs at risk (small bowel loops, bladder, femoral heads, pelvic bone marrow) are contoured with dose-volume histogram curves demonstrating bone marrow-sparing technique.</image>

## Key Clinical Pearls

Total neoadjuvant therapy has become the preferred approach for managing locally advanced rectal cancer. Both the RAPIDO and PRODIGE 23 trials demonstrated that TNT leads to higher pathologic complete response rates and lower distant metastasis rates compared to traditional preoperative CRT followed by adjuvant chemotherapy. For patients considering a watch-and-wait strategy, the OPRA trial established that delivering CRT followed by consolidation chemotherapy, rather than induction chemotherapy followed by CRT, results in higher organ preservation rates. Assessing clinical complete response requires a multimodality evaluation including digital rectal examination, endoscopy, and MRI, with timing of assessment at 8 to 12 weeks post-treatment to avoid premature conclusions. Importantly, local regrowth during watch-and-wait is not catastrophic; over 95% of regrowths can be salvaged with total mesorectal excision, and oncologic outcomes remain favorable when salvage surgery is performed promptly. Finally, bone marrow-sparing IMRT represents a significant technical advance in rectal cancer radiation therapy, reducing hematologic toxicity during concurrent CRT, which improves chemotherapy compliance and reduces treatment interruptions.

## References
- Sauer R et al. "Preoperative versus postoperative chemoradiotherapy for rectal cancer." *N Engl J Med*. 2004;351(17):1731-1740.
- Bahadoer RR et al. "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." *Lancet Oncol*. 2021;22(1):29-42.
- Conroy T et al. "Neoadjuvant chemotherapy with FOLFIRINOX and preoperative chemoradiotherapy for patients with locally advanced rectal cancer (UNICANCER-PRODIGE 23): a multicentre, randomised, open-label, phase 3 trial." *Lancet Oncol*. 2021;22(5):702-715.
- Garcia-Aguilar J et al. "Organ preservation in patients with rectal adenocarcinoma treated with total neoadjuvant therapy." *J Clin Oncol*. 2022;40(23):2546-2556.
- van der Valk MJM et al. "Long-term outcomes of clinical complete responders after neoadjuvant treatment for rectal cancer in the International Watch & Wait Database (IWWD): an international multicentre registry study." *Lancet*. 2018;391(10139):2537-2545.