Diagnostic accuracy of magnetic resonance imaging for rectal cancer: is it time to reassess the gold standard?

Tan Jih Huei; Emile John Tan Kwong Wei

doi:10.3393/ac.2025.01312.0187

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Letter to the Editor Colorectal cancer Diagnostic accuracy of magnetic resonance imaging for rectal cancer: is it time to reassess the gold standard?: Tan Jih Huei¹, Emile John Tan Kwong Wei^2,3; Annals of Coloproctology 2026;42(2):256-257.
DOI: https://doi.org/10.3393/ac.2025.01312.0187
Published online: April 29, 2026

¹Department of General Surgery, Hospital Sultanah Aminah, Johor Bahru, Malaysia

²Department of Colorectal Surgery, Singapore General Hospital, Singapore

³Department of Colorectal Surgery, National Cancer Centre Singapore, Singapore

Correspondence to: Emile John Tan Kwong Wei, MBBS, MD Department of Colorectal Surgery, National Cancer Centre Singapore, Singapore General Hospital, Outram Rd, Singapore 169608 Email: emilekwtan@gmail.com

• Received: November 2, 2025 • Accepted: November 17, 2025

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Dear Editor,

In response to the 2023 article published in Annals of Coloproctology entitled “Impact of consolidation chemotherapy in poor responders to neoadjuvant radiation therapy: magnetic resonance imaging–based clinical-radiological correlation in high-risk rectal cancers” [1], we concur with the authors’ observations regarding the inconsistency between magnetic resonance imaging (MRI)-based staging and intraoperative or histopathological findings.

Since the landmark MERCURY study in the early 2000s, MRI has been recognized as a highly accurate tool for assessing circumferential resection margin involvement and predicting long-term oncologic outcomes in rectal cancer based on preoperative local staging [2]. The same group subsequently demonstrated that posttreatment MRI retained similar prognostic value for survival when used to evaluate tumor response after neoadjuvant therapy [3].

However, in real-world practice, surgeons frequently encounter discordance between MRI-based staging and clinical interpretation, and this discrepancy is even more pronounced following neoadjuvant treatment. A 2015 meta-analysis by Memon et al. [4] reported that endorectal ultrasound (ERUS) showed a nonsignificant trend toward superior accuracy compared with MRI in T-staging after neoadjuvant chemoradiation (ERUS: 65%, 95% confidence interval [CI], 56%–72%; MRI: 52%, 95% CI, 44%–59%). They also noted that overstaging occurred more frequently than understaging (72% vs. 10%–15%).

In contrast, a 2020 meta-analysis involving 1,262 patients reported good diagnostic accuracy of MRI for predicting locoregional staging after neoadjuvant therapy [5]. The pooled sensitivity and specificity of MRI for detecting T3–T4 disease were 81% (95% CI, 67%–90%) and 67% (95% CI, 51%–80%), respectively. For nodal metastasis, the reported sensitivity and specificity were both 77% (sensitivity: 95% CI, 65%–86%; specificity: 95% CI, 63%–87%). Taken together, these findings suggest that despite significant technological advancements, MRI still functions as an imperfect gold standard for local staging of rectal cancer.

The accuracy of MRI for nodal staging also remains a topic of debate. Although MRI was historically regarded as less reliable in this context, a recent 2024 validation study involving 139 patients showed that refined morphologic criteria substantially improved diagnostic accuracy and interstudy consistency [6].

Another important limitation of MRI is interobserver variability. A study by a group of radiologists from the Netherlands, evaluating 36 MRI interpretations, found only moderate agreement among radiologists when assessing non-numerical characteristics such as border irregularity, shape, and apparent diffusion coefficient values. Such variability can lead to clinical misclassification, particularly in borderline scenarios such as T2 vs. early T3, mesorectal fascia (MRF) positive vs. T4a, and T4a vs. T4b disease. As highlighted by El Khababi et al. [7], MRI tends to overstage T2 tumors as T3, which may prompt overtreatment. Conversely, cT4a tumors with MRF involvement are sometimes understaged as T3 MRF positive, since readers may not recognize that peritoneal and MRF invasion can coexist. To address this, they proposed a dichotomized structured MRI reporting system to improve reproducibility and staging consistency.

In addition, adherence to recommended imaging protocols remains inadequate. A recent audit found that only 49% of restaging MRIs were performed according to the recommended sequences and protocol standards [8].

Clinically, these limitations create two major dilemmas for rectal cancer surgeons. The first dilemma is whether to operate on patients with a complete clinical response (cCR) on MRI, as misclassification remains common. In one study, among patients who ultimately achieved a pathologic complete response (pCR) after neoadjuvant therapy, MRI correctly identified only 44% of true pCR cases [9]. Although MRI showed high specificity (88.9%) for excluding non-pCR patients, its low sensitivity highlights the ongoing risk of both overtreatment and undertreatment. Consequently, decisions to omit surgery in cCR cases should be made cautiously, and patients should be fully informed of the potential risks of recurrence.

Another dilemma is whether to recommend upfront surgery or preoperative neoadjuvant therapy. Although early data from the MERCURY study supported the accuracy of MRI [2], subsequent studies highlighted high interobserver variability [7], calling for simplified or dichotomous classification systems to support surgical decision-making.

Looking ahead, artificial intelligence (AI)-based MRI analysis represents a promising advance for achieving more objective and reproducible assessments [10].

Despite continuous improvements in MRI technology and interpretation, meaningful limitations persist in its diagnostic accuracy for rectal cancer staging, particularly in the post-neoadjuvant setting. Surgeons should therefore interpret imaging findings within the broader clinical context, incorporating endoscopic assessment, digital rectal examination, and multidisciplinary review when formulating treatment strategies. Looking forward, the integration of AI into MRI analysis offers considerable potential for enhancing diagnostic precision and may represent a key step toward more individualized staging and management of rectal cancer.

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Conflict of interest

Emile John Tan Kwong Wei is an editorial board member of this journal, but was not involved in the peer reviewer selection, evaluation, or decision process of this article. No other potential conflict of interest relevant to this article was reported.

Funding

None.

REFERENCES

1. Patel S, Ankathi S, Haria P, Kazi M, Desouza AL, Saklani A. Impact of consolidation chemotherapy in poor responders to neoadjuvant radiation therapy: magnetic resonance imaging–based clinical-radiological correlation in high-risk rectal cancers. Ann Coloproctol 2023;39:474–83. Article PubMed PMC PDF
2. Taylor FG, Quirke P, Heald RJ, Moran BJ, Blomqvist L, Swift IR, et al. Preoperative magnetic resonance imaging assessment of circumferential resection margin predicts disease-free survival and local recurrence: 5-year follow-up results of the MERCURY study. J Clin Oncol 2014;32:34–43. Article PubMed
3. Patel UB, Taylor F, Blomqvist L, George C, Evans H, Tekkis P, et al. Magnetic resonance imaging-detected tumor response for locally advanced rectal cancer predicts survival outcomes: MERCURY experience. J Clin Oncol 2011;29:3753–60. Article PubMed
4. Memon S, Lynch AC, Bressel M, Wise AG, Heriot AG. Systematic review and meta-analysis of the accuracy of MRI and endorectal ultrasound in the restaging and response assessment of rectal cancer following neoadjuvant therapy. Colorectal Dis 2015;17:748–61. Article PubMed
5. Wei MZ, Zhao ZH, Wang JY. The diagnostic accuracy of magnetic resonance imaging in restaging of rectal cancer after preoperative chemoradiotherapy: a meta-analysis and systematic review. J Comput Assist Tomogr 2020;44:102–10. Article PubMed
6. Crimì F, Cabrelle G, Campi C, Schillaci A, Bao QR, Pepe A, et al. Nodal staging with MRI after neoadjuvant chemo-radiotherapy for locally advanced rectal cancer: a fast and reliable method. Eur Radiol 2024;34:3205–14. Article PubMed PDF
7. El Khababi N, Beets-Tan RG, Curvo-Semedo L, Tissier R, Nederend J, Lahaye MJ, et al. Pearls and pitfalls of structured staging and reporting of rectal cancer on MRI: an international multireader study. Br J Radiol 2023;96:20230091.Article PubMed PMC
8. Prata I, Eriksson M, Krdzalic J, Kranenbarg EM, Roodvoets AG, Beets-Tan R, et al. Results of a diagnostic imaging audit in a randomised clinical trial in rectal cancer highlight the importance of careful planning and quality control. Insights Imaging 2023;14:206.Article PubMed PMC PDF
9. Arndt K, Vigna C, Kaul S, Fabrizio A, Cataldo T, Smith M, et al. Magnetic resonance imaging accuracy in staging early and locally advanced rectal cancer. Surg Oncol 2023;50:101987.Article PubMed
10. Selby HM, Son YA, Sheth VR, Wagner TH, Pollom EL, Morris AM. AI-ready rectal cancer MR imaging: a workflow for tumor detection and segmentation. BMC Med Imaging 2025;25:88.Article PubMed PMC PDF

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