Comparison of MRI response evaluation methods in rectal cancer: a multicentre and multireader validation study

ESR Essentials: Imaging in colorectal cancer-practice recommendations by ESGAR

Colorectal cancer (CRC) is a significant global health concern. Diagnostic imaging, using different modalities, has a pivotal role in CRC, from early detection (i.e., screening) to follow-up. The role of imaging in CRC screening depends on each country's approach: if an organized screening program is in place, the role of CT colonography (CTC) is limited to the study of either individuals with a positive stool test unwilling/unable to undergo colonoscopy (CC) or in patients with incomplete CC. Although CC is the most common modality to diagnose CRC, CRC can be also incidentally detected during a routine abdominal imaging examination or at the emergency room in patients presenting with intestinal occlusion/subocclusion or perforation. Staging is a crucial aspect of CRC management, guiding treatment decisions and providing valuable prognostic information. An accurate local staging is mandatory in both rectal and colon cancer to drive the appropriate therapeutic workflow. Important limitations of US, CT, and MR in N-staging can be partially solved by FDG PET/CT. Distant staging is usually managed by CT, with MR and FDG PET/CT which can be used as problem-solving techniques. Follow-up is performed according to the general recommendations of the oncological societies. CLINICAL RELEVANCE STATEMENT: It is essential to summarize each phase of colorectal cancer workup, differentiating the management for colon and rectal cancer supported by the main international guidelines and literature data, with the aim to inform the community on the best practice imaging in colorectal cancer. KEY POINTS: • Colorectal cancer is a prevalent disease that lends itself to imaging at each stage of detection and management. • Various imaging modalities can be used as adjuncts to, or in place of, direct visualization methods of screening and are necessary for evaluating metastatic disease. • Reevaluation of follow-up strategies should be considered depending on patients' individual risk of recurrence.

Split scar sign to predict complete response in rectal cancer after neoadjuvant chemoradiotherapy: systematic review and meta-analysis

OBJECTIVES

Magnetic resonance imaging (MRI) is the modality of choice for rectal cancer initial staging and restaging after neoadjuvant chemoradiation. Our objective was to perform a meta-analysis of the diagnostic performance of the split scar sign (SSS) on rectal MRI in predicting complete response after neoadjuvant therapy.

METHODS

MEDLINE, EMBASE, and Cochrane databases were searched for relevant published studies through June 2023. Primary studies met eligibility criteria if they evaluated the diagnostic performance of the SSS to predict complete response on pathology or clinical follow-up in patients undergoing neoadjuvant chemoradiation. A meta-analysis with a random-effects model was used to estimate pooled sensitivity and specificity, area under the curve (AUC), and diagnostic odds ratio (DOR) of the SSS.

RESULTS

A total of 4 studies comprising 377 patients met the inclusion criteria. The prevalence of complete response in the studies was 21.7-52.5%. The pooled sensitivity and specificity of the SSS to predict complete response were 62.0% (95% CI, 43.5-78.5%) and 91.9% (95% CI, 78.9-97.2%), respectively. The estimated AUC for SSS was 0.83 (95% CI, 0.56-0.94) with a DOR of 18.8 (95% CI, 3.65-96.5).

CONCLUSION

The presence of SSS on rectal MRI demonstrated high specificity for complete response in patients with rectal cancer after neoadjuvant chemoradiation. This imaging pattern can be a valuable tool to identify potential candidates for organ-sparing treatment and surveillance.

CLINICAL RELEVANCE STATEMENT

SSS presents high specificity for complete response post-neoadjuvant. This MRI finding enhances rectal cancer treatment assessment and aids clinicians and patients in choosing watch-and-wait over immediate surgery, which can potentially reduce costs and associated morbidity.

KEY POINTS

•Fifteen to 50% of rectal cancer patients achieve complete response after neoadjuvant chemoradiation and may be eligible for a watch-and-wait strategy. •The split scar sign has high specificity for a complete response. •This imaging finding is valuable to select candidates for organ-sparing management.

Multi-omics staging of locally advanced rectal cancer predicts treatment response: a pilot study

Treatment response assessment of rectal cancer patients is a critical component of personalized cancer care and it allows to identify suitable candidates for organ-preserving strategies. This pilot study employed a novel multi-omics approach combining MRI-based radiomic features and untargeted metabolomics to infer treatment response at staging. The metabolic signature highlighted how tumor cell viability is predictively down-regulated, while the response to oxidative stress was up-regulated in responder patients, showing significantly reduced oxoproline values at baseline compared to non-responder patients (p-value < 10-4). Tumors with a high degree of texture homogeneity, as assessed by radiomics, were more likely to achieve a major pathological response (p-value < 10-3). A machine learning classifier was implemented to summarize the multi-omics information and discriminate responders and non-responders. Combining all available radiomic and metabolomic features, the classifier delivered an AUC of 0.864 (± 0.083, p-value < 10-3) with a best-point sensitivity of 90.9% and a specificity of 81.8%. Our results suggest that a multi-omics approach, integrating radiomics and metabolomic data, can enhance the predictive value of standard MRI and could help to avoid unnecessary surgical treatments and their associated long-term complications.

Clinical Tools for Rectal Cancer Response Assessment following Neoadjuvant Treatment in the Era of Organ Preservation

Local tumor response evaluation following neoadjuvant treatment(s) in rectal adenocarcinoma requires a multi-modality approach including physical and endoscopic evaluations, rectal protocoled MRI, and cross-sectional imaging. Clinical tumor response exists on a spectrum from complete clinical response (cCR), defined as the absence of clinical evidence of residual tumor, to near-complete response (nCR), which assumes a significant reduction in tumor burden but with increased uncertainty of residual microscopic disease, to incomplete clinical response (iCR), which incorporates all responses less than nCR that is not progressive disease. This article aims to review the clinical tools currently routinely available to evaluate treatment response and offers a potential management approach based on the extent of local tumor response.

Sense and non-sense of imaging in the era of organ preservation for rectal cancer

This review summarizes the current applications and benefits of imaging modalities for organ preservation in the treatment of rectal cancer. The concept of organ preservation in the treatment of rectal cancer has revolutionized the way rectal cancer is managed. Initially, organ preservation was limited to patients with locally advanced rectal cancer who needed neoadjuvant therapy to reduce tumor size before surgery and achieved complete response. However, neoadjuvant therapy is now increasingly utilized for smaller and less aggressive tumors to achieve primary organ preservation. Additionally, more intensive neoadjuvant strategies are employed to improve complete response rates and increase the chances of successful organ preservation. The selection of patients for organ preservation is a critical component of treatment, and imaging techniques such as digital rectal exam, endoscopy, and MRI are commonly used for this purpose. In this review, we provide an overview of what imaging modalities should be chosen and how they can aid in the selection and follow-up of patients undergoing organ-preserving strategies.

Pearls and pitfalls of structured staging and reporting of rectal cancer on MRI: an international multireader study

OBJECTIVES

To investigate uniformity and pitfalls in structured radiological staging of rectal cancer.

METHODS

Twenty-one radiologists (12 countries) staged 75 rectal cancers on MRI using a structured reporting template. Interobserver agreement (IOA) was calculated as the percentage agreement between readers (categorical variables) and Krippendorff's α (continuous variables). Agreement with an expert consensus served as a surrogate standard of reference to estimate diagnostic accuracy. Polychoric correlation coefficients were used to assess correlations between diagnostic confidence and accuracy (=agreement with expert consensus).

RESULTS

Uniformity to diagnose high-risk (≥cT3 ab) versus low-risk (≤cT3 cd) cT-stage, cN0 versus cN+, lateral nodes and tumour deposits, MRF and sphincter involvement, and solid versus mucinous tumours was high with IOA > 80% in the majority of cases (and >80% agreement with expert consensus). Results for assessing extramural vascular invasion, cT-stage (cT1-2/cT3/cT4a/cT4b), cN-stage (cN0/N1/N2), relation to the peritoneal reflection, extent of sphincter involvement (internal/intersphincteric/external) and morphology (solid/annular/semi-annular) were considerably poorer. IOA was high (α = 0.72-0.84) for tumour height/length and extramural invasion depth, but low for tumour-MRF distance and number of (suspicious) nodes (α = 0.05-0.55). There was a significant positive correlation between diagnostic confidence and accuracy (=agreement with expert consensus) (p < 0.001-p = 0.003).

CONCLUSIONS

- Several staging items lacked sufficient reproducibility.- Results for cT- and N-staging g improved when using a dichotomized stratification.- Considering the significant correlation between diagnostic confidence and accuracy, a confidence level may be incorporated into structured reporting for specific items with low reproducibility.

ADVANCES IN KNOWLEDGE

Although structured reporting aims to achieve uniformity in reporting, several items lack sufficient reproducibility and might benefit from dichotomized assessment and incorporating confidence levels.

[Interpretation of Rectal MRI after Neoadjuvant Treatment in Patients with Rectal Cancer]

MRI is currently the imaging modality of choice to evaluate rectal cancer after neoadjuvant treatment. The purposes of restaging MRI are to assess the resectability of rectal cancer and to decide whether organ preservation strategies can be applied in patients with a complete clinical response. This review article indicates the key MRI features needed to evaluate rectal cancer after neoadjuvant treatment using a systematic approach. Assessment of primary tumor response including MRI findings to predict a complete response is discussed. Additionally, MRI evaluation of the relationship between the primary tumor and adjacent structures, lymph node response, extramural venous invasion, and tumor deposits after neoadjuvant treatment is presented. Knowledge of these imaging features and their clinical relevance may help radiologists provide an accurate and clinically valuable interpretation of restaging rectal MRI.