# MRI After Total Neoadjuvant Therapy for Rectal Cancer: A Guide to Response Assessment and Watch-and-Wait Management This review article explains how magnetic resonance imaging (MRI) is changing the way doctors assess rectal cancer after total neoadjuvant therapy (TNT). TNT is a treatment approach that gives chemotherapy and radiation before surgery. The authors describe how restaging MRI now helps identify patients with a clinical complete response (cCR) or near-complete response (nCR) who may safely avoid surgery through a watch-and-wait approach. The article details specific MRI criteria used in major clinical trials, including the OPRA trial, and explains why doctors are shifting toward more sensitive imaging thresholds. It also covers the timing of restaging MRI, the role of endoscopy and digital rectal examination, and the need for further standardization. # MRI After Total Neoadjuvant Therapy for Rectal Cancer: A Guide to Response Assessment and Watch-and-Wait Management ## Table of Contents - Key Points - Background: Why This Research Matters - What Is Total Neoadjuvant Therapy? - Treatment-Oriented MRI Reporting - Key Clinical Trials That Changed Practice - MRI Interpretation Tailored to Different Treatments - The Shift in Diagnostic Threshold - What Is a Near-Complete Response? - Using Endoscopy, Digital Rectal Examination, and MRI Together - Timing of Restaging MRI - Clinical Implications for Patients - Limitations and Unanswered Questions - Recommendations - Frequently Asked Questions - Source Information ## Key Points - TNT gives all chemotherapy before surgery and is endorsed as a preferred approach for locally advanced rectal cancer, producing higher complete response rates than older treatment methods. - In the OPRA trial, patients with clinical complete or near-complete response were offered watch-and-wait; organ preservation occurred in about 53% in the consolidation arm. - MRI response categories alone in the OPRA trial were linked to 5-year disease-free survival: 81.8% for clinical complete response, 67.6% for near-complete, and 49.6% for incomplete. - During watch-and-wait, MRI is recommended every 3–4 months for 2 years, then every 6 months for 3 years; MRI may detect regrowth earlier than endoscopy in some cases. - Near-complete response is now accepted for watch-and-wait with close surveillance, as about half of these patients later achieve clinical complete response with comparable 2-year outcomes. ## Background: Why This Research Matters Rectal cancer treatment has changed significantly in recent years. A treatment approach called total neoadjuvant therapy (TNT) is now increasingly recognized as a standard option for locally advanced rectal cancer. The National Comprehensive Cancer Network (NCCN) guidelines endorse TNT as the preferred approach for this condition. This shift matters because TNT produces higher rates of complete tumor disappearance than older treatment methods. When the tumor disappears completely, some patients may be able to avoid surgery altogether. This approach is called nonoperative management or watch-and-wait. As more patients achieve complete responses, MRI has become more important than ever. MRI is now central to identifying which patients can safely skip surgery and which patients still need an operation. This review article describes how TNT and the growing use of nonoperative management have expanded the role of MRI in rectal cancer care. ## What Is Total Neoadjuvant Therapy? Total neoadjuvant therapy (TNT) is an alternative to conventional chemoradiotherapy (CRT). Conventional CRT gives chemotherapy and radiation together before surgery, with additional chemotherapy after surgery. TNT moves all systemic chemotherapy to before surgery instead of after. This change offers several advantages. TNT lowers treatment-related toxicity (harmful side effects). It improves how many patients complete their full course of systemic therapy. It is also associated with better control of distant disease (cancer that has spread to other parts of the body) and higher rates of pathologic complete response (pCR). A pathologic complete response means no cancer cells are found when the surgical specimen is examined under a microscope. Higher pCR rates mean more patients may be eligible for organ-preserving approaches that avoid permanent removal of the rectum. ## Treatment-Oriented MRI Reporting In the past, restaging MRI after conventional chemoradiotherapy served mainly to assess how much the tumor had shrunk and to help plan surgery. MRI provided useful information about mesorectal fascia involvement (whether the cancer touches the fatty tissue surrounding the rectum) and pelvic sidewall lymph nodes. However, this information rarely changed the treatment plan because all patients proceeded to total mesorectal excision (TME) surgery unless distant metastases appeared during treatment. This pattern held true even in early TNT trials. In the RAPIDO trial, patients with high-risk locally advanced rectal cancer were randomly assigned to either standard long-course CRT or TNT. The TNT group received short-course radiotherapy (5 sessions of 5 Gy each) followed by 6 cycles of CAPOX chemotherapy or 9 cycles of FOLFOX4 chemotherapy. All patients in both groups underwent TME surgery after neoadjuvant therapy. Similarly, in the PRODIGE-23 trial, patients with cT3–T4M0 rectal cancer were randomly assigned to standard CRT or TNT. The TNT group received induction FOLFIRINOX chemotherapy followed by long-course CRT. Again, TME surgery was performed in both groups. In these early trials, restaging MRI did not change patient management. This mirrored the limited role MRI played in the conventional CRT setting. A major shift came with the OPRA trial. This trial redefined restaging MRI as a central tool for deciding between nonoperative management and surgery. The OPRA trial compared two different TNT sequences in patients with stage II–III rectal cancer: - **Induction chemotherapy followed by chemoradiotherapy** - **Chemoradiotherapy followed by consolidation chemotherapy** After completing TNT, patients underwent restaging with MRI, flexible sigmoidoscopy, and digital rectal examination (DRE). Flexible sigmoidoscopy is a tube with a camera to look inside the rectum. DRE is a finger examination of the rectum. Based on these assessments, doctors categorized responses as: - **Clinical complete response (cCR)** — no visible tumor - **Near-complete response (nCR)** — mostly fibrosis with small residual spots - **Incomplete response (iCR)** — significant residual tumor Patients with cCR or nCR were offered a nonoperative watch-and-wait approach. Patients with iCR proceeded to surgery. In this context, MRI directly influenced whether patients would undergo immediate surgery or be managed without surgery. The OPRA trial was also unique because it was the first to allow observation of the natural history of tumor regression after treatment. It did not mandate immediate surgery for patients who lacked a complete response at initial evaluation. This demonstrated that delayed complete responses are common and that organ preservation can be safely achieved in selected patients. The trial also highlighted the continuous critical role of MRI during extended follow-up. MRI helps confirm sustained remission and enables early detection of tumor regrowth. ## Key Clinical Trials That Changed Practice The PROSPECT trial provided another example of treatment-oriented MRI use, though in a different clinical context. Patients with cT2N+ or T3 rectal cancer were randomly assigned to conventional CRT or a chemotherapy-first strategy using modified FOLFOX. In the FOLFOX arm, patients who showed at least 20% tumor reduction proceeded directly to TME surgery. Patients with less than 20% reduction received additional long-course CRT (50.4 Gy with concurrent 5-fluorouracil) before surgery. Only 9.1% of patients in the FOLFOX arm ultimately required preoperative CRT. Disease-free survival and overall survival were non-inferior to the standard CRT group. Prior trials, including OPRA and CAO/ARO/AIO-12, demonstrated that upfront CRT followed by consolidation chemotherapy yields higher complete response rates than induction chemotherapy followed by CRT. The PROSPECT trial now provides an alternative chemotherapy-first approach aimed at avoiding radiotherapy. This approach is becoming increasingly relevant given the rising incidence of rectal cancer among younger patients of reproductive age who may wish to preserve fertility. Although all patients in the PROSPECT trial ultimately underwent TME surgery, MRI played a critical response-adapted role by determining the need for additional radiotherapy. ## MRI Interpretation Tailored to Different Treatments With the diversification of treatment strategies for rectal cancer, restaging MRI interpretation must be tailored to each patient's specific treatment regimen. For example, some patients receive neoadjuvant chemotherapy alone without radiotherapy, as in the PROSPECT trial. In these patients, assessment of tumor response is less likely to be confounded by post-radiation edema (swelling) or fibrosis (scar tissue). One study evaluated MRI performance for predicting pCR after neoadjuvant chemotherapy alone. The authors suggested that the relatively higher diagnostic performance compared with previous studies may be attributable to differences in post-treatment imaging characteristics according to radiation exposure. Consistent with this, the same group reported in a separate study that reduction in longitudinal tumor length was generally greater following chemotherapy alone than after CRT. This interpretation is further supported by a secondary analysis of the NRG-GI002 trial. That analysis demonstrated higher interobserver agreement among radiologists in chemotherapy-only cases than in cases that also received radiation. A similar consideration applies to patients with mismatch repair-deficient or microsatellite instability-high rectal cancer treated with immunotherapy without radiotherapy. Pseudoprogression or pseudo-residual tumor is a well-recognized phenomenon in other malignancies treated with immunotherapy. This means that an apparent increase in tumor size may not necessarily indicate true disease progression. However, it remains unclear whether a similar phenomenon applies in rectal cancer, given the relative novelty of immunotherapy in this setting. ## The Shift in Diagnostic Threshold Another emerging paradigm shift concerns the diagnostic threshold used to define complete tumor response on MRI. Historically, radiologists have adopted a conservative approach to minimize the risk of misclassifying patients with residual tumors as complete responders. This conservative approach is reflected in meta-analytic performance for predicting pCR following CRT. Sensitivity was relatively low at 62%, compared with specificity at 89%. While this approach prioritized oncologic safety, it also led to potentially unnecessary surgery in some patients who had, in fact, achieved pCR. More recently, this rigid threshold appears to be shifting toward a more sensitive interpretation. Doctors are now accepting a slightly higher false-positive rate for cCR in exchange for expanding eligibility for organ-preserving strategies. This conceptual shift is evident in evolving eligibility criteria for watch-and-wait management. The initial report from the International Watch & Wait Database (IWWD), a global registry comprising data from over 60 centers in 15 countries, included only patients who achieved cCR after neoadjuvant therapy. In contrast, the OPRA trial expanded eligibility to include both cCR and nCR. This broader inclusion criterion was based on observations that approximately one-half of patients with nCR at initial restaging ultimately achieve cCR with additional observation time. The OPRA trial confirmed the feasibility of this broader approach. It reported organ preservation in approximately 53% of patients in the consolidation arm, with most cases of local regrowth successfully managed with delayed TME. Consistently, analysis of the updated IWWD data demonstrated that 402 patients with nCR on initial restaging who later achieved cCR during continued follow-up had comparable 2-year oncologic outcomes to 608 patients who had cCR on initial restaging. Together, these findings suggest that many patients with nCR can safely be considered for organ preservation without compromising oncologic outcomes. Reflecting this growing body of evidence, the 2023 consensus statement from the Society of Abdominal Radiology Colorectal and Anal Cancer Disease-Focused Panel recommended grouping nCR with cCR. This recommendation applies provided that such patients undergo close surveillance with MRI and flexible sigmoidoscopy. With nCR now accepted as eligible for watch-and-wait management, radiologists are under less pressure to reserve the designation of cCR exclusively for cases demonstrating an unequivocal complete response. Improved pCR rates achieved with TNT represent another factor contributing to this diagnostic shift from prioritizing high specificity toward high sensitivity in assessing complete response. This can be intuitively understood: radiologists are generally more confident assigning a cCR in a patient cohort known to have a higher prevalence of pCR. This trend has also been demonstrated quantitatively. In a retrospective study comparing strategies for combining T2-weighted and diffusion-weighted imaging (DWI) to predict pCR after CRT, the F1 score (the harmonic mean of sensitivity and positive predictive value) of the "OR" strategy surpassed that of the "AND" strategy at a pCR rate of 36.6% or higher. The "OR" strategy classified cases as complete responders if either mrTRG 1–2 or absence of diffusion restriction was observed. The "AND" strategy required both criteria to be met. These findings suggest that diagnostic strategies aimed at higher sensitivity may become more favorable as the pCR rate improves. The pCR rates achieved with TNT are approximately double those observed with standard CRT. In the RAPIDO trial, pCR rates were 28.4% with TNT versus 14.3% with standard CRT. In the PRODIGE-23 trial, pCR rates were 27.5% with TNT versus 11.7% with standard CRT. These rates are expected to increase further with ongoing advancements in chemotherapy regimens. Notably, the impact of increased pCR rates on the diagnostic shift toward sensitivity-oriented interpretation remains relevant even in countries where nonoperative management is rarely adopted in routine practice. However, the clinical implications may be less pronounced than in settings where watch-and-wait strategies are frequently employed. ## What Is a Near-Complete Response? The term nCR conceptually refers to cases demonstrating substantial tumor regression at initial restaging that may subsequently progress to cCR over time. However, the specific radiologic criteria defining nCR remain poorly standardized and vary considerably across the literature. In the OPRA trial, nCR on T2-weighted imaging was defined as "mostly fibrosis with one or two punctate foci of intermediate T2 signal." In contrast, iCR was described as "predominantly intermediate rather than dark T2 signal intensity." A cCR corresponded to a "normal-appearing rectal wall." On DWI, nCR was characterized by marked regression of high b-value signal relative to baseline. For extraluminal disease (cancer outside the rectum), nCR was defined as partial regression of lymph nodes from baseline with a residual short-axis diameter of 5 mm or larger. Recent expert consensus guidelines acknowledge that imaging criteria for nCR cannot yet be precisely standardized. However, they propose the following guiding principles: 1. **nCR should represent a very good but incomplete response** at initial reassessment, with the potential to evolve into cCR over time. 1. **nCR should be considered a temporary classification**, applicable only within the first 6 months after completion of neoadjuvant therapy. Beyond this period, tumor response should be definitively classified as either cCR or iCR. ## Using Endoscopy, Digital Rectal Examination, and MRI Together MRI remains an indispensable tool for post-treatment assessment of rectal cancer. This is partly because MRI enables evaluation of the mesorectum for lymph nodes, extramural venous invasion (EMVI, cancer cells invading veins outside the rectum), and tumor deposits. These features cannot be assessed by endoscopy. Data from the OPRA trial demonstrated that MRI-based categorization of cCR, nCR, and iCR alone, regardless of endoscopic findings, is associated with both oncologic outcomes and rates of organ preservation. Specifically, MRI response categories stratified 5-year disease-free survival as follows: - **cCR:** 81.8% disease-free survival - **nCR:** 67.6% disease-free survival - **iCR:** 49.6% disease-free survival Additionally, participants with cCR had a higher 5-year organ preservation rate than those with nCR (65.3% vs. 41.6%). Discrepancies between endoluminal evaluation by sigmoidoscopy and MRI are not uncommon. Among 116 patients classified as having cCR on restaging MRI in the OPRA trial, 12 were advised to undergo surgery based on findings of sigmoidoscopy. Three of these 12 patients were confirmed to have pCR. Among 125 patients categorized as nCR, 27 proceeded to surgery, and five were found to have pCR. Currently, there is no clear consensus on how to integrate three modalities—MRI, sigmoidoscopy, and DRE—when discrepancies arise. Although a recent consensus guideline suggests placing greater emphasis on endoscopic assessment over MRI interpretation, robust evidence establishing the superiority of either modality is lacking. Moreover, a prior study demonstrated that MRI may detect tumor regrowth earlier than endoscopy in a subset of cases. MRI can visualize the full thickness of the rectal wall and extraluminal disease. Further standardization of MRI criteria for nCR and subsequently improved interobserver agreement may expand the role of MRI in patient management. ## Timing of Restaging MRI A previous international consensus statement recommended that tumor reassessment using MRI, endoscopy, and DRE for determination of cCR be performed 24–38 weeks after treatment initiation. The exact timing depends on the treatment regimen and its duration. However, the statement did not provide detailed guidance regarding the necessity and timing of additional MRI examinations, such as those performed between CRT and systemic chemotherapy. Prior clinical trials have demonstrated variability in MRI utilization: - **RAPIDO, PRODIGE-23, and OPRA trials:** MRI was performed at baseline and after completion of all neoadjuvant therapy. - **PRODIGE-23 and OPRA trials:** An interim MRI was also performed after the first treatment component, either systemic chemotherapy or CRT, whichever was administered first. - **RAPIDO trial:** Additional MRI during systemic chemotherapy was optional and left to the discretion of the treating clinician. - **PROSPECT trial:** Restaging MRI was performed before and after chemotherapy. However, additional MRI before surgery was not mandated for patients who subsequently received radiotherapy. The same guideline further recommends that, once a watch-and-wait strategy is initiated, patients undergo MRI every 3–4 months during the first 2 years. This is followed by MRI every 6 months for the next 3 years. Further consensus on the optimal timing of restaging MRI is essential. Treatment response evolves over time and may be significantly influenced by the timing of imaging. ## Clinical Implications for Patients This review has several important implications for patients with rectal cancer: - **More patients may avoid surgery.** With TNT producing higher complete response rates, more patients may be eligible for watch-and-wait management. - **MRI is central to treatment decisions.** MRI, combined with endoscopy and DRE, helps doctors determine whether a patient can safely skip surgery. - **Near-complete responses are now acceptable for watch-and-wait.** Patients with nCR can be offered nonoperative management with close surveillance, rather than proceeding directly to surgery. - **Regular surveillance is essential.** Patients undergoing watch-and-wait need MRI every 3–4 months for the first 2 years, then every 6 months for the next 3 years. - **Tumor regrowth can be detected early.** MRI can detect tumor regrowth earlier than endoscopy in some cases, allowing for timely intervention. For patients with nCR who later achieve cCR during continued follow-up, 2-year oncologic outcomes are comparable to those who had cCR on initial restaging. This means that many patients with nCR can safely be considered for organ preservation without compromising their cancer outcomes. ## Limitations and Unanswered Questions The authors acknowledge several limitations and areas needing further research: - **No standardized criteria for nCR.** The specific radiologic criteria defining nCR remain poorly standardized and vary considerably across the literature. - **No consensus on integrating modalities.** There is no clear consensus on how to integrate MRI, sigmoidoscopy, and DRE when discrepancies arise. - **Uncertainty about immunotherapy.** It remains unclear whether pseudoprogression applies in rectal cancer treated with immunotherapy, given the relative novelty of immunotherapy in this setting. - **Optimal timing of MRI is unclear.** Further consensus on the optimal timing of restaging MRI is essential, as treatment response evolves over time. - **Need for validation.** Further standardization and validation are needed to define imaging criteria for nCR. Further standardization and validation are also needed to determine optimal timing and frequency of restaging MRI. Further standardization and validation are needed to establish how imaging findings should be integrated with endoscopic and clinical data. ## Recommendations Based on this review, the following recommendations can be made for patients with rectal cancer considering TNT and watch-and-wait management: 1. **Discuss TNT with your medical team.** TNT is now a preferred approach for locally advanced rectal cancer and may increase your chances of avoiding surgery. 1. **Understand the role of MRI.** MRI is essential for assessing treatment response and determining whether you are eligible for watch-and-wait management. 1. **Complete all recommended imaging.** Follow your doctor's recommendations for restaging MRI, endoscopy, and DRE to accurately assess your response to treatment. 1. **Attend all surveillance appointments.** If you undergo watch-and-wait management, regular MRI every 3–4 months for the first 2 years and every 6 months for the next 3 years is recommended. 1. **Report any new symptoms.** If you experience new rectal bleeding, pain, or changes in bowel habits during watch-and-wait, contact your medical team promptly. 1. **Ask about your response category.** Understanding whether you have cCR, nCR, or iCR can help you make informed decisions about your care. ## Frequently Asked Questions ### What is total neoadjuvant therapy (TNT) for rectal cancer? TNT moves all systemic chemotherapy to before surgery instead of after, unlike conventional chemoradiotherapy. It lowers treatment-related toxicity, improves how many patients complete their full course of systemic therapy, and is associated with better control of distant disease and higher rates of pathologic complete response. The National Comprehensive Cancer Network guidelines endorse TNT as the preferred approach for locally advanced rectal cancer. ### Can I avoid surgery if my rectal cancer disappears after treatment? Some patients whose tumor disappears completely after TNT may avoid surgery through a watch-and-wait approach. In the OPRA trial, patients with a clinical complete response or near-complete response were offered nonoperative management. The trial reported organ preservation in approximately 53% of patients in the consolidation arm, with most local regrowth successfully managed by delayed surgery. ### What do clinical complete response, near-complete response, and incomplete response mean? These are response categories used after TNT. A clinical complete response means no visible tumor. A near-complete response means mostly fibrosis with small residual spots. An incomplete response means significant residual tumor. In the OPRA trial, patients with clinical complete or near-complete response were offered watch-and-wait, while those with incomplete response proceeded to surgery. ### How often will I need MRI scans during watch-and-wait? Once a watch-and-wait strategy is started, an international consensus statement recommends MRI every 3 to 4 months during the first 2 years, followed by MRI every 6 months for the next 3 years. Regular surveillance is essential because treatment response evolves over time and MRI can detect tumor regrowth earlier than endoscopy in some cases. ### Why is MRI used together with endoscopy and digital rectal examination? MRI can assess the mesorectum for lymph nodes, extramural venous invasion, and tumor deposits, which endoscopy cannot. In the OPRA trial, MRI response categories alone were associated with 5-year disease-free survival: 81.8% for clinical complete response, 67.6% for near-complete response, and 49.6% for incomplete response. Discrepancies between endoscopy and MRI are not uncommon. ### What are the risks of choosing watch-and-wait instead of surgery? The main risk is tumor regrowth, which is why close surveillance with MRI and flexible sigmoidoscopy is required. In the OPRA trial, most cases of local regrowth were successfully managed with delayed total mesorectal excision. For patients with near-complete response who later achieved clinical complete response during follow-up, 2-year oncologic outcomes were comparable to those who had clinical complete response initially. ### What should I do if I notice new symptoms during watch-and-wait? If you experience new rectal bleeding, pain, or changes in bowel habits during watch-and-wait, contact your medical team promptly. Regular surveillance appointments and completing all recommended imaging, endoscopy, and digital rectal examination help accurately assess your response. Ask your team about your response category, as understanding whether you have clinical complete, near-complete, or incomplete response can help you make informed decisions. ### If I have a near-complete response on MRI after total neoadjuvant therapy for rectal cancer, should I get a second opinion before deciding on watch-and-wait or surgery? Response category drives the decision. MRI categories stratify 5-year disease-free survival: 81.8% for clinical complete response, 67.6% for near-complete response, and 49.6% for incomplete response. Near-complete response is now accepted for watch-and-wait with close MRI and sigmoidoscopy surveillance, since about half of these patients later reach complete response with comparable 2-year outcomes. Criteria for near-complete response remain poorly standardized, and no consensus exists on integrating MRI, sigmoidoscopy, and digital rectal examination when they disagree, so an independent review of your imaging can help clarify your category. Diagnostic Detectives Network provides independent expert second opinions. ## Source Information **Original Article Title:** Magnetic Resonance Imaging After Total Neoadjuvant Therapy in Rectal Cancer: Treatment-Oriented Response Assessment and Reporting for Watch-and-Wait Management. **Journal:** Korean journal of radiology **License:** CC BY-NC (open access) **Authors:** Kim HY, Jang JK, Gollub MJ. **Author Affiliations:** Department of Radiology and Research Institute of Radiology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Republic of Korea; Department of Radiology, Memorial Sloan Kettering Cancer Center, New York, NY, USA **Publication:** Korean Journal of Radiology, 2026;27(7):652-659 **DOI:** https://doi.org/10.3348/kjr.2026.0046 **Received:** January 10, 2026 | **Revised:** April 5, 2026 | **Accepted:** April 9, 2026 **Conflicts of Interest:** The authors have no potential conflicts of interest to disclose. **Funding:** None *This patient-friendly article is based on peer-reviewed research.* --- Publisher: Diagnostic Detectives Network (https://diagnosticdetectives.com) — independent multi-expert medical second opinions, worldwide, private-pay. Author byline: Anton Titov, MD, PhD. Contact: https://diagnosticdetectives.com/pages/contact Canonical page: https://diagnosticdetectives.com/products/mri-after-total-neoadjuvant-therapy-for-rectal-cancer-a-guide-to-response-assessment-and-watch-and-wait-management