Correction to: Magnetic resonance imaging for clinical management of rectal cancer: Updated recommendations from the 2016 European Society of Gastrointestinal and Abdominal Radiology (ESGAR) consensus meeting

Preoperative lateral lymph node features and impact on local recurrence after neoadjuvant chemoradiotherapy and total mesorectal excision for locally advanced rectal cancer: results from a multicentre international cohort study

AIM

Locally advanced rectal cancer (LARC) is commonly treated with neoadjuvant chemoradiotherapy (nCRT) and total mesorectal excision (TME) to reduce local recurrence (LR) and improve survival. However, LR, particularly associated with lateral lymph node (LLN) involvement, remains a concern. The aim of this study was to investigate preoperative factors associated with LLN involvement and their impact on LR rates in LARC patients undergoing nCRT and curative surgery.

METHOD

This multicentre retrospective study, including four academic high-volume institutions, involved 301 consecutive adult LARC patients treated with nCRT and curative surgery between January 2014 and December 2019 who did not undergo lateral lymph node dissection (LLND). Baseline and restaging pelvic MRIs were evaluated for suspicious LLNs based on institutional criteria. Patients were divided into two groups: cLLN+ (positive nodes) and cLLN- (no suspicious nodes). Primary outcome measures were LR and lateral local recurrence (LLR) rates at 3 years.

RESULTS

Among the cohort, 15.9% had suspicious LLNs on baseline MRI, and 9.3% had abnormal LLNs on restaging MRI. At 3 years, LR and LLR rates were 4.0% and 1.0%, respectively. Ten out of 12 (83.3%) patients with LR showed no suspicious LLNs at the baseline MRI. Abnormal LLNs on MRI were not independent risk factors for LR, distant recurrence or disease-free survival.

CONCLUSION

Abnormal LLNs on baseline and restaging MRI assessment did not impact LR and LLR rates in this cohort of patients with LARC submitted to nCRT and curative TME surgery.

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.

Surgical Considerations for Neoadjuvant Therapy for Pancreatic Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is a challenging disease process with a 5-year survival rate of only 11%. Neoadjuvant therapy in patients with localized pancreatic cancer has multiple theoretical benefits, including improved patient selection for surgery, early delivery of systemic therapy, and assessment of response to therapy. Herein, we review key surgical considerations when selecting patients for neoadjuvant therapy and curative-intent resection. Accurate determination of resectability at diagnosis is critical and should be based on not only anatomic criteria but also biologic and clinical criteria to determine optimal treatment sequencing. Borderline resectable or locally advanced pancreatic cancer is best treated with neoadjuvant therapy and resection, including vascular resection and reconstruction when appropriate. Lastly, providing nutritional, prehabilitation, and supportive care interventions to improve patient fitness prior to surgical intervention and adequately address the adverse effects of therapy is critical.

Artificial intelligence and radiomics in magnetic resonance imaging of rectal cancer: a review

Rectal cancer (RC) is one of the most common tumours worldwide in both males and females, with significant morbidity and mortality rates, and it accounts for approximately one-third of colorectal cancers (CRCs). Magnetic resonance imaging (MRI) has been demonstrated to be accurate in evaluating the tumour location and stage, mucin content, invasion depth, lymph node (LN) metastasis, extramural vascular invasion (EMVI), and involvement of the mesorectal fascia (MRF). However, these features alone remain insufficient to precisely guide treatment decisions. Therefore, new imaging biomarkers are necessary to define tumour characteristics for staging and restaging patients with RC. During the last decades, RC evaluation via MRI-based radiomics and artificial intelligence (AI) tools has been a research hotspot. The aim of this review was to summarise the achievement of MRI-based radiomics and AI for the evaluation of staging, response to therapy, genotyping, prediction of high-risk factors, and prognosis in the field of RC. Moreover, future challenges and limitations of these tools that need to be solved to favour the transition from academic research to the clinical setting will be discussed.

Rectal MRI Interpretation After Neoadjuvant Therapy

In recent years, several key advances in the management of locally advanced rectal cancer have been made, including the implementation of total mesorectal excision as the standard surgical approach; use of neoadjuvant chemoradiotherapy in selected patients with a high risk of local recurrence, and finally, adoption of organ preservation strategies, through either local excision or nonoperative management in selected patients with clinical complete response following neoadjuvant chemoradiotherapy. This review aims to shed light on the role of rectal MRI in the assessment of treatment response after neoadjuvant therapy, which is especially important given the growing feasibility of nonoperative management. First, an overview of current neoadjuvant therapies and response assessment based on digital rectal examination, endoscopy, and MRI will be provided. Second, the use of a high-quality restaging rectal MRI protocol will be presented. Third, a step-by-step approach to assessing treatment response on restaging rectal MRI following neoadjuvant treatment will be outlined, acknowledging challenges faced by radiologists during MRI interpretation. Finally, research related to response assessment will be discussed. LEVEL OF EVIDENCE: 4 TECHNICAL EFFICACY: Stage 3.

Structured and shared MRI staging lexicon and report of rectal cancer: A consensus proposal by the French Radiology Group (GRERCAR) and Surgical Group (GRECCAR) for rectal cancer

PURPOSE

To develop French guidelines by experts to standardize data acquisition, image interpretation, and reporting in rectal cancer staging with magnetic resonance imaging (MRI).

MATERIALS AND METHODS

Evidence-based data and opinions of experts of GRERCAR (Groupe de REcherche en Radiologie sur le CAncer du Rectum [i.e., Rectal Cancer Imaging Research Group]) and GRECCAR (Groupe de REcherche en Chirurgie sur le CAncer du Rectum [i.e., Rectal Cancer Surgery Research Group]) were combined using the RAND-UCLA Appropriateness Method to attain consensus guidelines. Experts scoring of reporting template and protocol for data acquisition were collected; responses were analyzed and classified as "Recommended" versus "Not recommended" (when ≥ 80% consensus among experts) or uncertain (when < 80% consensus among experts).

RESULTS

Consensus regarding patient preparation, MRI sequences, staging and reporting was attained using the RAND-UCLA Appropriateness Method. A consensus was reached for each reporting template item among the experts. Tailored MRI protocol and standardized report were proposed.

CONCLUSION

These consensus recommendations should be used as a guide for rectal cancer staging with MRI.

Interobserver variability in MRI measurements of mesorectal invasion depth in rectal cancer

PROPOSE

To assess the interobserver variability in MRI measurements of mesorectal invasion depth (MID) in rectal adenocarcinomas primarily staged as T3, by determining the level of interobserver agreement in the differentiation of individual T3 substages and of T3a-b vs. T3c-d disease, between readers with different levels of expertise.

METHODS

A retrospective analysis of 60 patients classified by MRI as having T3 rectal cancers was performed. Each patient underwent MR examination in a 1.5 T machine and the standard imaging protocol included a high-resolution axial T2-weighted sequence in which the measurements were determined by independent radiologists (readers A and B, with 15 years and 1 year of experience, respectively). The rectum was further divided into quadrants and each reader selected the quadrant where the measurement was taken. The patients were grouped according to the MID (T3a < 1 mm; T3b 1-5 mm; T3c > 5-15 mm; T3d > 15 mm) and the interobserver reliability was tested using Cohen's kappa.

RESULTS

Population included 40 males and 20 females with a median age of 65.9 years. Interobserver agreement on individual substage differentiation (T3 a, b, c and d) was moderate (K = 0.428) and in the quadrant evaluation the level of agreement was also moderate (K = 0.414). Nevertheless, the interobserver reliability for the differentiation between stages T3a-b vs. T3c-d was substantial (K = 0.697).

CONCLUSIONS

There is no considerable interobserver variability when distinguishing T3a-b from T3c-d tumors, regardless of the quadrant where the MID is measured. Therefore, assessment of MID, for that purpose, is a reproducible MR parameter, irrespectively of the readers' experience.

Poor response at restaging MRI and high incomplete resection rates of locally advanced mucinous rectal cancer after chemoradiation therapy

AIM

Mucinous carcinoma is a histological subtype of rectal cancer and has been associated with a poor response to neoadjuvant chemoradiotherapy (CRT). The primary aim of this study was to analyse the response on MRI of mucinous locally advanced rectal cancer (LARC) after CRT compared to regular adenocarcinoma.

METHOD

Patients with LARC (defined as cT4 and/or cN2), who underwent CRT followed by restaging MRI and surgery in two tertiary referral hospitals were retrospectively included in the study. Pre- and post-treatment MRI was reviewed by an experienced abdominal radiologist.

RESULTS

A total of 102 patients, of whom 29 were diagnosed with mucinous carcinoma, were included for analysis. At restaging MRI, adenocarcinoma patients demonstrated significantly less clinical involvement of the mesorectal fascia (37% vs. 62%, P = 0.003) while this was not demonstrated in mucinous carcinoma patients (86% vs. 97%, P = 0.16). Significant downstaging after CRT in adenocarcinoma patients (P = 0.01) was seen while, in mucinous carcinoma patients, no downstaging after CRT (P = 0.89) was seen. Pathology revealed significantly higher rates of an involved circumferential resection margin in mucinous carcinoma versus adenocarcinoma patients (27.6% vs. 1.4%; P < 0.001). After multivariate regression analysis, mucinous carcinoma remained an independent prognostic factor for local recurrence (hazard ratio 3.6; 95% CI 1.1-12.4), although no differences in overall or disease-free survival were observed.

CONCLUSION

Mucinous rectal carcinoma is associated with a poor clinical response at restaging MRI after CRT, leading to relatively higher rates of involved circumferential resection margins at pathology. In this cohort, mucinous carcinoma seems to be a prognostic factor for increased risk of local recurrence, without an effect on overall survival.

A Pipeline for Predicting the Treatment Response of Neoadjuvant Chemoradiotherapy for Locally Advanced Rectal Cancer Using Single MRI Modality: Combining Deep Segmentation Network and Radiomics Analysis Based on "Suspicious Region"

Patients with locally advanced rectal cancer (LARC) who achieve a pathologic complete response (pCR) after neoadjuvant chemoradiotherapy (nCRT) typically have a good prognosis. An early and accurate prediction of the treatment response, i.e., whether a patient achieves pCR, could significantly help doctors make tailored plans for LARC patients. This study proposes a pipeline of pCR prediction using a combination of deep learning and radiomics analysis. Taking into consideration missing pre-nCRT magnetic resonance imaging (MRI), as well as aiming to improve the efficiency for clinical application, the pipeline only included a post-nCRT T2-weighted (T2-w) MRI. Unlike other studies that attempted to carefully find the region of interest (ROI) using a pre-nCRT MRI as a reference, we placed the ROI on a “suspicious region”, which is a continuous area that has a high possibility to contain a tumor or fibrosis as assessed by radiologists. A deep segmentation network, termed the two-stage rectum-aware U-Net (tsraU-Net), is designed to segment the ROI to substitute for a time-consuming manual delineation. This is followed by a radiomics analysis model based on the ROI to extract the hidden information and predict the pCR status. The data from a total of 275 patients were collected from two hospitals and partitioned into four datasets: Seg-T (N = 88) for training the tsraUNet, Rad-T (N = 107) for building the radiomics model, In-V (N = 46) for internal validation, and Ex-V (N = 34) for external validation. The proposed method achieved an area under the curve (AUC) of 0.829 (95% confidence interval [CI]: 0.821, 0.837) on In-V and 0.815 (95% CI, 0.801, 0.830) on Ex-V. The performance of the method was considerable and stable in two validation sets, indicating that the well-designed pipeline has the potential to be used in real clinical procedures.

An MRI-based multi-objective radiomics model predicts lymph node status in patients with rectal cancer

PURPOSE

To apply a multi-objective radiomics model based on pre-operative magnetic resonance imaging (MRI) for improving diagnostic accuracy of LN metastasis in rectal cancer patients.

METHODS

This study consisted of 91 patients diagnosed with rectal cancer from April 2018 to March 2019. All patients underwent rectal MRI before surgery without any other treatment. Clinical data, subjective radiologist assessments, and radiomic features of LNs were obtained. A total of 1409 radiomic features were extracted from T2WI LN images. Multi-objective optimization with the iterative multi-objective immune algorithm (IMIA) was used to select radiomic features to build prediction models. Predictive performances of radiomic, radiologist, and combined radiomic and radiologist models were assessed for accuracy by receiver operating characteristics (ROC) curves.

RESULTS

For the radiologist analysis, heterogeneity was the only significant independent predictor of LN status. The sensitivity, specificity, and accuracy of the subjective radiologist analysis were 72.09%, 73.81%, and 78.12%, respectively. The sensitivity, specificity, and accuracy of the solitary radiomic model consisting of 10 features were 89.81%, 82.57%, and 87.77%, respectively. The sensitivity, specificity, and accuracy of the combined model, which consisted of 12 radiomic and radiologist features, were 92.23%, 84.69%, and 89.88%, respectively. The combined model had the best prediction performance with an AUC of 0.94.

CONCLUSIONS

The multi-objective radiomics model based on T2WI images was very useful in predicting pre-operative LN status in rectal cancer patients.

The Heterogeneity of Skewness in T2W-Based Radiomics Predicts the Response to Neoadjuvant Chemoradiotherapy in Locally Advanced Rectal Cancer

Our study aimed to investigate whether radiomics on MRI sequences can differentiate responder (R) and non-responder (NR) patients based on the tumour regression grade (TRG) assigned after surgical resection in locally advanced rectal cancer (LARC) treated with neoadjuvant chemoradiotherapy (nCRT). Eighty-five patients undergoing primary staging with MRI were retrospectively evaluated, and 40 patients were finally selected. The ROIs were manually outlined in the tumour site on T2w sequences in the oblique-axial plane. Based on the TRG, patients were grouped as having either a complete or a partial response (TRG = (0,1), n = 15). NR patients had a minimal or poor nCRT response (TRG = (2,3), n = 25). Eighty-four local first-order radiomic features (RFs) were extracted from tumour ROIs. Only single RFs were investigated. Each feature was selected using univariate analysis guided by a one-tailed Wilcoxon rank-sum. ROC curve analysis was performed, using AUC computation and the Youden index (YI) for sensitivity and specificity. The RF measuring the heterogeneity of local skewness of T2w values from tumour ROIs differentiated Rs and NRs with a p-value ≈ 10⁻⁵; AUC = 0.90 (95%CI, 0.73–0.96); and YI = 0.68, corresponding to 80% sensitivity and 88% specificity. In conclusion, higher heterogeneity in skewness maps of the baseline tumour correlated with a greater benefit from nCRT.

Management of the adenocarcinoma of the upper rectum: a reappraisal

The present review attempts to assess whether upper rectal cancer (URC) should be treated either as colon cancer or as rectal one, namely to be managed with upfront surgery without neo-adjuvant treatment and partial mesorectal excision (PME), or with neo-adjuvant short course radiotherapy (SCRT) or chemoradiotherapy (CRT) as indicated, followed by surgery with total mesorectal excision. Reports from current evidence including studies, reviews and various guidelines are conflicting. Main reasons for inability to reach safe conclusions are (i) the various anatomical definitions of the rectum and its upper part, (ii) the inadequate preoperative local staging,(iii) the heterogeneity of selection criteria for the neo-adjuvant treatment,(iv) the different neo-adjuvant treatment regimens, and(v) the variety in the extent of surgical resection, among the studies. Although not adequately supported, locally advanced URC can be treated with neo-adjuvant CRT provided the lesion is within the radiation field of safety, and a PME if the lower border of the tumour is located above the anterior peritoneal reflection. There is evidence that adjuvant chemotherapy is of benefit in high-risk stage II and stage III lesions.

Watch-and-Wait Compared to Operation for Patients with Complete Response to Neoadjuvant Therapy for Rectal Cancer

BACKGROUND

Trimodality therapy with neoadjuvant chemoradiation (nCRT), surgery, and adjuvant chemotherapy is the standard treatment for locally advanced rectal cancer. There is evidence that surgery can be deferred in patients with complete response (CR) to nCRT, a strategy termed "watch-and-wait" (WW). We compare WW to surgery in patients with CR to nCRT.

STUDY DESIGN

We reviewed records of patients treated with nCRT for nonmetastatic rectal cancer at our institution. Complete endoscopic response (CER) was defined as negative digital rectal exam and negative endoscopy at the end of neoadjuvant therapy (NAT). Clinical complete response (cCR) was defined as CER with negative rectal MRI. Patients with CER refusing surgery were offered WW, which included strict surveillance with digital rectal exam and endoscopy.

RESULTS

From January 2015 through February 2019, 465 patients completed nCRT; 406 patients had response assessment, of which 95 (23%) had CER. Of these patients, 53 patients underwent WW and 42 patients had surgery. Median follow-up was 35 months. In the WW group, 3-year freedom from local regrowth was 85%. In the surgical and WW groups, 3-year overall survival, rectal cancer-specific survival, and freedom from nonregrowth recurrence were 100% vs 88% (p = 0.03), 100% vs 95% (p = 0.16), and 92% vs 85% (p = 0.36), respectively. Of the 6 WW patients with local regrowth, 5 (83%) eventually developed distant recurrence.

CONCLUSIONS

WW in lieu of surgery appears to be a safe and feasible treatment approach for patients achieving CR to nCRT. Careful evaluation to confirm cCR after nCRT is valuable in selecting patients for WW.

Tumour growth rate of carcinoma of the colon and rectum: retrospective cohort study

BACKGROUND

The growth pattern of colorectal cancer is seldom investigated. This cohort study aimed to explore tumour growth rate in colorectal cancers managed non-surgically or deemed not resectable, and to determine its implication for prognosis.

METHODS

Consecutive patients with colonic or rectal adenocarcinoma were identified through the colorectal multidisciplinary team database at Leeds Teaching Hospitals NHS Trust over a 2-year interval. Patients who received no treatment (surgery, stenting, colonic defunctioning procedures, chemotherapy, radiotherapy) and who underwent CT twice more than 5 weeks apart were included. Multidetector CT/three-dimensional image analysis was performed independently by three experienced radiologists.

RESULTS

Of 804 patients reviewed, 43 colorectal cancers were included in the final analysis. Median age at first CT was 80 (73-85) years and the median interval between scans was 150 (i.q.r. 72-471) days. An increase in T category was demonstrated in 31 of 43 tumours, with a median doubling time of 211 (112-404) days. The median percentage increase in tumour volume was 34·1 (13·3-53·9) per cent per 62 days. The all-cause 3-year mortality rate was 81 per cent (35 of 43) with a median survival time of 1·1 (0·4-2·2) years after the initial diagnostic scan. In those obstructed, the relative risk of death from subsequent perforation was 1·26 (95 per cent c.i. 1·07 to 1·49; P = 0·005).

CONCLUSION

This study documented a median doubling time of 211 days, with a concerning suggestion of tumour progression, which has implications for the current management standard.

MRI response rate after short-course radiotherapy on rectal cancer in the elderly comorbid patient: results from a retrospective cohort study

Background

The aim of the present study was to evaluate MRI response rate and clinical outcome of short-course radiotherapy (SCRT) on rectal cancer as an alternative to chemoradiotherapy in patients where downstaging is indicated.

Methods

A retrospective analysis was performed of a patient cohort with rectal carcinoma (cT1-4cN0-2 cM0–1) from a large teaching hospital receiving restaging MRI, deferred surgery or no surgery after SCRT between 2011 and 2017. Patients who received chemotherapy during the interval between SCRT and restaging MRI were excluded.

The primary outcome measure was the magnetic resonance tumor regression grade (mrTRG) at restaging MRI after SCRT followed by a long interval. Secondary, pathological tumor stage, complete resection rate and 1-year overall survival were assessed.

Results

A total of 47 patients (M:F = 27:20, median age 80 (range 53–88) years), were included. In 33 patients MRI was performed for response assessment 10 weeks after SCRT. A moderate or good response (mrTRG≤3) was observed in 24 of 33 patients (73%). While most patients (85%; n = 28) showed cT3 or cT4 stage on baseline MRI, a ypT3 or ypT4 stage was found in only 20 patients (61%) after SCRT (p <  0.01). A complete radiologic response (mrTRG 1) was seen in 4 patients (12%). Clinical N+ stage was diagnosed in n = 23 (70%) before SCRT compared to n = 8 (30%) post-treatment (p = 0.03).

After SCRT, 39 patients underwent deferred surgery (after a median of 14 weeks after start of SCRT) and a resection with complete margins was achieved in 35 (90%) patients. One-year overall survival after surgery was 82%. Complete pathological response was found in 2 patients (5%).

Conclusions

The use of SCRT followed by a long interval to restaging showed a moderate to good response in 73% and therefore can be considered as an alternative to chemoradiotherapy in elderly comorbid patients.

Imaging of rectal cancer

International guidelines dictate that magnetic resonance imaging (MRI) should be part of the primary standard work up of patients with rectal cancer because MRI can accurately identify the main risk factors for local recurrence and stratify patients into a differentiated treatment. The role of endoscopic ultrasound (EUS) is restricted to staging of superficial tumors because EUS is able to differentiate between T1 and T2 rectal cancer. Recent guidelines recommend the addition of diffusion-weighted (DWI) MRI to clinical and endoscopic assessment of response to preoperative radiochemotherapy (RCT). MRI is able to identify significant tumor regression which may alter the surgical approach.

Mucinous rectal cancer: concepts and imaging challenges

Rectal adenocarcinoma with mucinous components is an uncommon type of rectal cancer with two distinct histologic subtypes: mucinous adenocarcinoma and signet-ring cell carcinoma. Mucin can also be identified as pattern of response after neoadjuvant treatment. On imaging modalities, mucin typically demonstrates high signal intensity on T2-weighted images, low attenuation on computed tomography, and may be negative on 18-fluorodeoxyglucose positron emission tomography. After neoadjuvant CRT, cellular and acellular mucin share similar imaging features, and differentiating them is currently the main challenge faced by radiologists. Radiologists should be aware of pros, cons, and limitations of each imaging modality in the primary staging and restaging to avoid misinterpretation of the radiological findings.

Mucinous rectal cancer: concepts and imaging challenges

Rectal adenocarcinoma with mucinous components is an uncommon type of rectal cancer with two distinct histologic subtypes: mucinous adenocarcinoma and signet-ring cell carcinoma. Mucin can also be identified as pattern of response after neoadjuvant treatment. On imaging modalities, mucin typically demonstrates high signal intensity on T2-weighted images, low attenuation on computed tomography, and may be negative on 18-fluorodeoxyglucose positron emission tomography. After neoadjuvant CRT, cellular and acellular mucin share similar imaging features, and differentiating them is currently the main challenge faced by radiologists. Radiologists should be aware of pros, cons, and limitations of each imaging modality in the primary staging and restaging to avoid misinterpretation of the radiological findings.

Creation of a rectal cancer registry in Italy by the Advanced International Mini-Invasive Surgery (AIMS) academy clinical research network

Background: The management of rectal cancer is multimodal and involves a multidisciplinary team of cancer specialists with expertise in medical oncology, surgical oncology, radiation oncology and radiology. It is crucial for highly specialized centers to collaborate via networks that aim to maintain uniformity in every aspect of treatment and rigorously gather patients’ data, from the first clinical evaluation to the last follow-up visit.

The Advanced International Mini-Invasive Surgery (AIMS) academy clinical research network aims to create a rectal cancer registry. This will prospectively collect the data of patients operated on for non-metastatic rectal cancer in high volume colorectal surgical units through a well design pre-fashioned database for non-metastatic rectal cancer, in order to take all multidisciplinary aspects into consideration.

Methods/Design: The protocol describes a multicenter prospective observational cohort study, investigating demographics, frailty, cancer-related features, surgical and radiological parameters, and oncological outcomes among patients with non-metastatic rectal cancer who are candidates for surgery with curative intent. Patients enrolled in the present registry will be followed up for 5 years after surgery.

Discussion: Standardization and centralization of data collection for neoplastic diseases is a virtuous process for patient care. The creation of a register will allow the control of the quality of treatments provided and permit prospective and retrospective studies to be carried out on complete and reliable high quality data. Establishing data collection in a prospective and systematic fashion is the only possibility to preserve the enormous resource that each patient represents.

[Imaging of rectal cancer. German version]

International guidelines dictate that magnetic resonance imaging (MRI) should be part of the primary standard work up of patients with rectal cancer because MRI can accurately identify the main risk factors for local recurrence and stratify patients into a differentiated treatment. The role of endoscopic ultrasound (EUS) is restricted to staging of superficial tumors because EUS is able to differentiate between T1 and T2 rectal cancer. Recent guidelines recommend the addition of diffusion-weighted (DWI) MRI to clinical and endoscopic assessment of response to preoperative radiochemotherapy (RCT). MRI is able to identify significant tumor regression which may alter the surgical approach.

Radiogenomics of rectal adenocarcinoma in the era of precision medicine: A pilot study of associations between qualitative and quantitative MRI imaging features and genetic mutations

OBJECTIVE

To investigate associations between genetic mutations and qualitative as well as quantitative features on MRI in rectal adenocarcinoma at primary staging.

METHODS

In this retrospective study, patients with rectal adenocarcinoma, genome sequencing, and pretreatment rectal MRI were included. Statistical analysis was performed to evaluate associations between qualitative features obtained from subjective evaluation of rectal MRI and gene mutations as well as between quantitative textural features and gene mutations. For the qualitative evaluation, Fisher's Exact test was used to analyze categorical associations and Wilcoxon Rank Sum test was used for continuous clinical variables. For the quantitative evaluation, we performed manual segmentation of T2-weighted images for radiomics-based quantitative image analysis. Thirty-four texture features consisting of first order intensity histogram-based features (n = 4), second order Haralick textures (n = 5), and Gabor-edge based Haralick textures were computed at two different orientations. Consensus clustering was performed with 34 computed texture features using the K-means algorithm with Euclidean distance between the texture features. The clusters resulting from the algorithm were then used to enumerate the prevalence of gene mutations in those clusters.

RESULTS

In 65 patients, 45 genes were mutated in more than 3/65 patients (5%) and were included in the statistical analysis. Regarding qualitative imaging features, on univariate analysis, tumor location was significantly associated with APC (p = 0.032) and RASA1 mutation (p = 0.032); CRM status was significantly associated with ATM mutation (p = 0.021); and lymph node metastasis was significantly associated with BRCA2 (p = 0.046) mutation. However, these associations were not significant after adjusting for multiple comparisons. Regarding quantitative imaging features, Cluster C1 had tumors with higher mean Gabor edge intensity compared with cluster C2 (θ = 0°, p = 0.018; θ = 45°, p = 0.047; θ = 90°, p = 0.037; cluster C3 (θ = 0°, p = 0.18; θ = 45°, p = 0.1; θ = 90°, p = 0.052), and cluster C4 (θ = 0°, p = 0.016; θ = 45°, p = 0.033; θ = 90°, p = 0.014) suggesting that the cluster C1 had tumors with more distinct edges or heterogeneous appearance compared with other clusters.

CONCLUSIONS

Although this preliminary study showed promising associations between quantitative features and genetic mutations, it did not show any correlation between qualitative features and genetic mutations. Further studies with larger sample size are warranted to validate our preliminary data.