Imaging in rectal cancer with emphasis on local staging with MRI

Watch & wait - Post neoadjuvant imaging for rectal cancer

Rectal cancer management has evolved over the past decade with the emergence of total neoadjuvant therapy (TNT). For select patients who achieve a clinical complete response following TNT, organ preservation by means of the watch-and-wait (WW) strategy is an increasingly adopted alternative that preserves rectal function and quality of life without compromising oncologic outcomes. Recently, published 5-year results from the OPRA trial demonstrated that organ preservation can be achieved in approximately half of patients managed with the WW strategy, with most local regrowth events occurring within two years. Considering the potential for local regrowth, the implementation of the WW strategy mandates rigorous clinical and radiographic surveillance. Magnetic resonance imaging (MRI) serves as the conventional imaging modality for local staging and surveillance of rectal cancer given its excellent soft-tissue resolution. This review will discuss the current evidence for the WW strategy and the role of restaging rectal MRI in determining patient eligibility for this strategy. Restaging rectal MRI acquisition parameters and treatment response assessment, including important factors to assess, pitfalls, and classification systems, will be discussed in the context of the WW strategy.

Disparities in Diagnostic Imaging for Initial Local Staging for Rectal Cancer

OBJECTIVE

To assess the presence, quality, and timeliness of initial staging imaging for rectal cancer patients, and to evaluate demographic factors associated with disparities.

METHODS

We conducted a chart review of consecutive rectal adenocarcinoma cancer registry cases from a single institution for the period from 2015 to 2020. We recorded whether initial staging MRI or endoscopic ultrasound (EUS) was performed, and whether it was performed in or outside the institution. MRI quality was assessed based on compliance to the Society of Abdominal Radiology rectal cancer disease-focused panel protocol recommendations. The times between diagnosis and imaging were calculated. Patients' age, race, ethnicity, sex, body mass index, address, and primary payer were acquired from the electronic medical record. Descriptive analysis, odds ratios, and Student's t tests were used for analysis.

RESULTS

Of 346 patients, 39% were female, and the average age was 59 years. A total of 93 patients (26.8%) had no initial staging MRI or endoscopic ultrasound. Of the 142 MRIs evaluated for image quality, 100 patient exams (72.4%) met the criteria for adequate quality. The mean time interval from diagnosis to imaging was 30.9 days. A lower likelihood of receiving initial local staging was associated with being of Hispanic ethnicity (P < .01), having Medicaid or no insurance (P < .01), and residing in a low-income census block (P < .01). Higher quality of imaging was associated with residence in a census block with high median income (P < 0.01), more recent diagnosis (P < .01), and MRI performed at the institution presented (P < .01).

CONCLUSIONS

Although radiologic workup variability was found across all demographics, sociodemographic factors have an effect on local initial imaging of rectal cancer, emphasizing the need to improve image acquisition for underserved patients and improve quality standardization at low-volume centers.

Evaluation of an Objective MRI-Based Tumor Regression Grade (mrTRG) Score and a Subjective Likert Score for Assessing Treatment Response in Locally Advanced Rectal Cancers-A Retrospective Study

Purpose:  Magnetic resonance imaging (MRI) with the help of MRI-based tumor regression grade (mrTRG) score has been used as a tool to predict pathological tumor regression grade (pTRG) in patients of rectal cancer post-neoadjuvant chemoradiation. Our study aims to evaluate the ability of MRI in assessing treatment response comparing an objective mrTRG score and a subjective Likert score, with a focus on the ability to predict pathologic complete response (pCR). Methods:  Post-treatment MRI studies were retrospectively reviewed for 170 consecutive cases of histopathologically proven rectal cancer after receiving neoadjuvant chemoradiation and prior to surgery by two oncoradiologists blinded to the eventual postoperative histopathology findings. An objective (mrTRG) and a subjective Likert score were assigned to all the cases. Receiver operating characteristic curves were constructed to determine the ability of Likert scale and mrTRG to predict pCR, with postoperative histopathology being the gold standard. The optimal cutoff points on the scale of 1 to 5 were obtained for mrTRG and Likert scale with the greatest sum of sensitivity and specificity using the Youden Index. Results:  The most accurate cutoff point for the mrTRG to predict complete response was 2.5 (using Youden index), with a sensitivity of 69.2%, specificity of 69.6%, positive predictive value (PPV) of 85.6%, negative predictive value (NPV) of 46.4%, and accuracy of 69.3%. The most accurate cutoff for the Likert scale to predict complete response was 3.5, with a sensitivity of 47.5%, specificity of 89.1%, PPV of 91.9%, NPV of 39.4%, and accuracy of 59%. mrTRG had a lower cutoff and was more accurate in predicting pCR compared to Likert score. Conclusion:  An objective mrTRG was more accurate than a subjective Likert scale to predict complete response in our study.

The Promise of Magnetic Resonance Imaging in Radiation Oncology Practice in the Management of Brain, Prostate, and GI Malignancies

Magnetic resonance imaging (MRI) has a key role to play at multiple steps of the radiotherapy (RT) treatment planning and delivery process. Development of high-precision RT techniques such as intensity-modulated RT, stereotactic ablative RT, and particle beam therapy has enabled oncologists to escalate RT dose to the target while restricting doses to organs at risk (OAR). MRI plays a critical role in target volume delineation in various disease sites, thus ensuring that these high-precision techniques can be safely implemented. Accurate identification of gross disease has also enabled selective dose escalation as a means to widen the therapeutic index. Morphological and functional MRI sequences have also facilitated an understanding of temporal changes in target volumes and OAR during a course of RT, allowing for midtreatment volumetric and biological adaptation. The latest advancement in linear accelerator technology has led to the incorporation of an MRI scanner in the treatment unit. MRI-guided RT provides the opportunity for MRI-only workflow along with online adaptation for either target or OAR or both. MRI plays a key role in post-treatment response evaluation and is an important tool for guiding decision making. In this review, we briefly discuss the RT-related applications of MRI in the management of brain, prostate, and GI malignancies.

Pictorial essay on MRI local staging of rectal carcinoma: An easy approach

Rectal cancer is common and accounts for more than one-third of colorectal tumors. It is associated with significant morbidity and mortality. Previously computed tomography scan is the key imaging modality in preoperative assessment to detect local invasion and distant metastasis. However, the advent of magnetic resonance imaging (MRI) has aided in local staging and prognosticates the outcome of rectal tumor. Here, the author briefly explains why rectal MRI has a comprehensive role and provides a simple and easy way in reporting an MRI rectal carcinoma, even for a non-radiologist.

How to accurately measure the distance from the anal verge to rectal cancer on MRI: a prospective study using anal verge markers

PURPOSE

To determine an accurate method for localizing rectal cancer using the distance from the anal verge on preoperative MRI.

METHODS

This prospective study included 50 patients scheduled for MRI evaluation of rectal cancer. After rectal filling with gel, MRI was performed with two markers attached at the anal verge. The distance between the tumor and the anal verge on a sagittal T2-weighted image (T2WI) was measured independently by two radiologists using six methods divided into three groups of similar measurement approaches, and compared to those obtained on rigid sigmoidoscopy. The anal verge location relative to the external anal sphincter was assessed on oblique coronal T2WI in reference to the markers. Correlation analysis was performed using the intraclass correlation coefficient (ICC) for verification, and a paired t test was used to evaluate the mean differences.

RESULTS

The highest correlation (ICC 0.797-0.815) and the least mean difference (0.74-0.85 cm) with rigid sigmoidoscopy, and the least standard deviation (3.12-3.17 cm) were obtained in the direct methods group using a straight line from the anal verge to the tumor. The anal verge was localized within a range of - 1.4 to 1.5 cm (mean - 0.31 cm and - 0.22 cm) from the lower end of the external anal sphincter.

CONCLUSION

The direct methods group provided the most accurate tumor distance among the groups. Among the direct methods, we recommend the direct mass method for its simplicity. Despite minor differences in location, the lower end of the external anal sphincter was a reliable anatomical landmark for the anal verge.

Systemic chemotherapy and short-course radiation in metastatic rectal cancers: A feasible paradigm in unresectable and potentially resectable cancers

Background:

The optimal use and sequencing of short-course radiotherapy (SCRT) in metastatic rectal cancers (mRCs) are not well established.

Materials and Methods:

We retrospectively reviewed the records of mRC patients receiving SCRT followed by palliative chemotherapy between January 1, 2013, and December 31, 2016, in Tata Memorial Hospital. Patients were classified as having “potentially resectable” disease (local and metastatic) or “unresectable” disease at baseline based on prespecified criteria.

Results:

A total of 105 consecutive patients were available for analysis. The median age of patients was 48 years (range: 16–62 years), and 57.1% were male patients. Signet ring histology was seen in 13.3% of patients. The most common site of metastases was liver limited (29.5%), nonloco-regional nodes (12.4%), and lung limited metastases (9.5%). Chemotherapeutic regimens administered were capecitabine-oxaliplatin (70.5%), modified 5 fluorouracil (5 FU)-leucovorin-irinotecan-oxaliplatin (10.5%), and modified 5 FU-leucovorin-irinotecan (8.6%). Targeted therapy accompanying chemotherapy was administered in 27.6% of patients. About 42.1% of patients with potentially resectable disease and 11.1% with the unresectable disease at baseline underwent curative-intent resection of the primary and address of metastatic sites. With a median follow-up 18.2 months, median overall survival (OS) was 15.7 months (95% confidence interval: 10.42–20.99). Patients classified as potentially resectable had a median OS of 32.62 months while patients initially classified as unresectable had a median OS of 13.04 months (P = 0.016). The presence of signet ring morphology predicted for inferior mOS (P = 0.021).

Conclusions:

SCRT followed by systemic therapy in mRC is a feasible, efficacious paradigm for maximizing palliation, and achieving objective responses. The classification of patients based on resectability was predictive of actual resection rates as well as outcomes. Signet ring mRC show inferior outcomes in this cohort of patients.

Radiological staging of rectal cancer in a resource limited setting

Objective

Current guidelines on rectal cancer (RC) management recommend pre-operative MRI for loco-regional staging and CT for staging of metastases. This allows appropriate selection of patients for chemo-radiotherapy (CRT). However, MRI is not freely available in many low-income countries. We assessed the status of pre-operative imaging for RC in Sri Lanka and evaluated the performance of CT in RC staging.

Results

A pre-tested interview-administered questionnaire was used to assess the pre-operative use of MRI and CT in RC. CT findings from 37 RC patients were then compared with histopathology findings. Of the 64 surgeons interviewed, 57 (89.1%) did not request an MRI for their RC patients. Reasons cited included limited availability and long waiting times due to competing health needs. A CT was requested by all. In RC, the overall accuracy of CT for T staging was 43.2% and 29.7% of T1–T2 tumours were over-staged as T3. The overall accuracy of CT for regional lymph node staging was 70.3%. In summary, CT alone is not suitable for RC staging in any setting. It leads to over-staging and patients may thus receive unnecessary CRT. Steps must be taken to improve access to pre-operative MRI among Sri Lankan RC patients.

Addition of short course radiotherapy in newly diagnosed locally advanced rectal cancers with distant metastasis

AIM

To study the outcomes of patients presenting with locally advanced rectal cancers with distant metastasis (mLARC), treated with short course radiotherapy (SCRT).

METHOD

Between May 2012 and August 2015, 70 patients diagnosed with mLARC, treated with SCRT (25 Gy/5#) and three to six cycles of CAPOX chemotherapy (CT), were assessed for surgical feasibility for the primary and metastatic sites.

RESULTS

Sixty-five patients could complete the planned SCRT and three to six cycles of CT. Response rate and disease control rate for the primary was 68% and 97%, respectively. Radiologically, CRM became free in 44 (72%) patients out of 61 initially involved. Fifty-two (74%) were planned to receive treatment with a potentially curative intent and 18 (26%) with palliative intent. Of those treated with curative intent, 34 (65%) underwent primary tumor resection (PTR). Successful intervention for metastatic disease was done in 27 (52%) patients. At a median follow up of 43 months, the median overall survival (OS) for patients undergoing PTR was 36 months versus 12 months for those in which the tumor was still unresectable or had distant progression (P < .001). Of the operated patients, 56% were alive at the end of 3 years. The median pelvic recurrence free survival was 29 months. Symptom control in the form of pain and bleeding control was observed in 80%.

CONCLUSION

The addition of SCRT to CT in mLARC can downstage the primary tumor to undergo surgery, thereby, achieving better loco-regional control and survival. It achieves good palliation in patients unable to undergo surgery due to extensive primary or metastatic disease.

Factors predicting recurrence after curative resection for rectal cancer: a 16-year study

BACKGROUND

The recurrence after curative surgery of the rectal adenocarcinoma is a serious complication, considered as a failure of the therapeutic strategy. The aim of this study was to identify the different prognostic factors affecting the recurrence of adenocarcinoma of the rectum.

METHODS

A retrospective analysis of patients operated for adenocarcinoma of the rectum between January 2000 and December 2015 was conducted. The study of the recurrence rate and prognostic factors was performed through the Kaplan Meier survival curve and the Cox regression analysis.

RESULTS

During the study period, 188 patients underwent curative surgery for rectal adenocarcinoma, among which 53 had a recurrence. The recurrence rate was 44.6% at 5 years. The multivariate analysis identified four parameters independently associated with the risk of recurrence after curative surgery: a distal margin ≤ 2 cm (HR = 6.8, 95% CI 2.7-16.6, 6), extracapsular invasion of lymph node metastasis (HR = 4.4, 95% CI 1.3-14), tumor stenosis (HR = 4.3, 95% CI 1.2-15.2), and parietal invasion (pT3/T4 disease) (HR = 3, 95% CI 1.1-9.4).

CONCLUSION

The determination of the prognostic factors affecting the recurrence of rectal adenocarcinoma after curative surgery allows us to define the high-risk patients for recurrence.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT03899870 . Registered on 2 February 2019, retrospectively registered.

EUS versus magnetic resonance imaging in staging rectal adenocarcinoma: a diagnostic test accuracy meta-analysis

BACKGROUND AND AIMS

EUS and magnetic resonance imaging (MRI) are both used for locoregional staging of rectal cancer, which determines treatment options. There is a lack of consensus on the best modality for locoregional staging, with studies supporting both EUS and MRI. In this study, we performed the first diagnostic test accuracy meta-analysis to compare the diagnostic accuracy, sensitivity, and specificity of EUS and MRI in the staging of rectal cancer.

METHODS

A comprehensive electronic literature search up to June 2018 was performed to identify prospective cohort studies directly comparing the accuracy of EUS with MRI in staging nonmetastatic rectal cancer with surgical pathology as the reference standard. Quality of the included studies was measured by using the Quality Assessment of Diagnostic Accuracy Studies (QUADAS-2) tool. A bivariate hierarchical model was used to perform the meta-analysis of diagnostic test accuracy according to the Cochrane approved methodology. Summary receiver operating characteristics were developed, and the area under the curve was calculated for overall and individual T and N staging, for EUS, MRI, and head-to-head comparison.

RESULTS

Six of 2475 studies including 234 patients were eligible. Pooled sensitivity and specificity in T staging were .79 (95% confidence interval [CI], .72-.85) and .89 (95% CI, .84-.93) for EUS and .79 (95% CI, .72-.85) and .85 (95% CI, .79-.90) for MRI, respectively. Pooled sensitivity and specificity in N staging were .81 (95% CI, .71-.89) and .88 (95% CI, .80-.94) for EUS and .83 (95% CI, .73-.90), and .90 (95% CI, .82-.95) for MRI, respectively. In area under the curve head-to-head analysis, EUS was superior to MRI in overall T staging (P < .05). EUS outperformed MRI in overall T, overall N, T1, and T3 staging (P < .01), after excluding studies using an endorectal coil for MRI. MRI was superior to EUS in T2 staging (P = .01) in both analyses.

CONCLUSIONS

EUS and MRI both provide reasonable diagnostic accuracy in the staging of nonmetastatic rectal cancer. EUS was superior to MRI in overall T staging and overall T and N staging after adjusting for MRI technology. Practitioners should be aware of advantages and disadvantages of both modalities and choose appropriate methods while considering diagnostic accuracy of each test and institutional practices and limitations.

Persistent involvement of anterior mesorectal fascia in carcinoma rectum - extended resection of rectum vs total pelvic exenteration: results from a single-centre retrospective study

AIM

Involvement of the anterior mesorectal fascia (iAMRF) after neoadjuvant treatment leads to either resection of the involved organ alone [extended resection of the rectum (ERR)] or total pelvic exenteration (TPE). The purpose of this study was to compare the rate of recurrence and survival of patients undergoing ERR or TPE for iAMRF after neoadjuvant treatment. The outcome of patients who underwent total mesorectal excision after downstaging was also compared.

METHOD

This was a retrospective study of primary rectal cancer patients.

RESULTS

Of 237 patients, 61 (21.5%) patients with nonmetastatic carcinoma rectum had iAMRF at baseline. Ten patients defaulted before completion of neoadjuvant chemoradiotherapy. After neoadjuvant chemoradiotherapy, 22 patients (43.1%) developed systemic metastases, seven patients (13.8%) were downstaged to free anterior mesorectal fascia and underwent total mesorectal excision (anterior resection/abdominoperineal resection) and the remaining 22 patients (43.1%) had persistent iAMRF. Thirteen patients with persistent iAMRF underwent ERR, whereas nine patients underwent TPE. The median duration of hospital stay in the TPE group was 13 days (10-26), whereas it was 7 days (5-21) in the ERR group. A clear circumferential resection margin, R0 resection, was achieved in all patients with TPE and ERR. After a median follow-up of 31.6 months, five patients with TPE (55.6%), four patients with ERR (30.7%) and three patients in the downstaged group (42.9%) developed systemic recurrence. None of the patients with TPE and the downstaged group developed local recurrence, whereas three patients with ERR (23.1%) developed local recurrence. Median disease-free survival was 12.3 months in the TPE group, 18.9 months in the ERR group and 10.6 months in the downstaged group, whereas mean overall survival was 36.2, 32.8 and 27.9 months, respectively.

CONCLUSION

Although there is no significant difference in the overall survival and disease-free survival, ERR is associated with a high risk of local recurrence compared to TPE and the downstaged group.

Low prevalence of deficient mismatch repair (dMMR) protein in locally advanced rectal cancers (LARC) and treatment outcomes

Background

The available evidence in locally advanced rectal cancer (LARC) suggests a low prevalence of deficient mismatch repair (dMMR) protein status, approximating 1-3%.

Methods

Patients with LARC who were offered long course chemoradiation (LCRT), as per institution protocol during the period of 1st January 2014 to 31st December 2015 at Tata Memorial Hospital (TMH) in Mumbai were evaluated for outcomes and assessment of MMR status.

Results

A total of 419 patients were evaluated for LARC in TMH, of whom 354 were treated with LCRT. Of these 354 patients, 296 were assessable for MMR status based on tissue adequacy for testing. Three patients (1.01%) has dMMR status, while the remaining 293 patients had proficient MMR status. A total of 240 patients (67.8%) underwent curative intent resections. With a median follow-up of 32 months, estimated 3-year recurrence free survival (RFS) and overall survival (OS) for the resected group was 63.5% and 85.2%, respectively, while 3-year event free survival and OS for the unresected cohort was 15.2% and 15.8%, respectively. Signet ring histology, higher ypT stage, involved margin status post resection, and delays (>1 week) in LCRT were associated with inferior OS on multivariate analysis.

Conclusions

In a large LARC cohort, a majority of tumors had proficient MMR status, suggesting that MSI as a biomarker may have limited applicability in the management of rectal cancers. Signet ring histology, CRM involvement post resection, higher ypT stage and interruptions in LCRT predicted for inferior OS.