The role of sequential 18(F) -FDG PET/CT in predicting tumour response after preoperative chemoradiation for rectal cancer

MRI VS. FDG-PET for diagnosis of response to neoadjuvant therapy in patients with locally advanced rectal cancer

Aim

In this study, we aimed to compare the diagnostic values of MRI and FDG-PET for the prediction of the response to neoadjuvant chemoradiotherapy (NACT) of patients with locally advanced Rectal cancer (RC).

Methods

Electronic databases, including PubMed, Embase, and the Cochrane library, were systematically searched through December 2021 for studies that investigated the diagnostic value of MRI and FDG-PET in the prediction of the response of patients with locally advanced RC to NACT. The quality of the included studies was assessed using QUADAS. The pooled sensitivity, specificity, positive and negative likelihood ratio (PLR and NLR), and the area under the ROC (AUC) of MRI and FDG-PET were calculated using a bivariate generalized linear mixed model, random-effects model, and hierarchical regression.

Results

A total number of 74 studies with recruited 4,105 locally advanced RC patients were included in this analysis. The pooled sensitivity, specificity, PLR, NLR, and AUC for MRI were 0.83 (95% CI: 0.77-0.88), 0.85 (95% CI: 0.79-0.89), 5.50 (95% CI: 4.11-7.35), 0.20 (95% CI: 0.14-0.27), and 0.91 (95% CI: 0.88-0.93), respectively. The summary sensitivity, specificity, PLR, NLR and AUC for FDG-PET were 0.81 (95% CI: 0.77-0.85), 0.75 (95% CI: 0.70-0.80), 3.29 (95% CI: 2.64-4.10), 0.25 (95% CI: 0.20-0.31), and 0.85 (95% CI: 0.82-0.88), respectively. Moreover, there were no significant differences between MRI and FDG-PET in sensitivity (P = 0.565), and NLR (P = 0.268), while the specificity (P = 0.006), PLR (P = 0.006), and AUC (P = 0.003) of MRI was higher than FDG-PET.

Conclusions

MRI might superior than FGD-PET for the prediction of the response of patients with locally advanced RC to NACT.

The impact of total neo-adjuvant treatment on nonoperative management in patients with locally advanced rectal cancer: The evaluation of 66 cases

BACKGROUND

The study aimed to assess if adherence to a total-neoadjuvant-treatment (TNT) protocol followed by observation(watch-and-wait) led to the successful nonoperative-management of low-rectal-cancer.

METHODS

In this study, patients with primary, resectable-T3-T4, N0-N1 distal-rectal-adenocarcinoma underwent-chemoradiotherapy + consolidation-chemotherapy (TNT). During the-TNT-period, endoscopy, MRI, and FDG-PET/CT were performed. We allocated patients with complete-clinical-tumor-regression, who underwent endoscopy every two months, MRI every-four-months, and PET/CT every-six-months-after-treatment, to the observation-group(OG). All other patients were referred for surgery. The OG was followed-up. The primary endpoint was local tumor-ecurrence after allocation to the OG.

RESULTS

Between 2015 and 2018, we enrolled 66-patients. Of 60-patients who were eligible to participate, 39 had complete-clinical-response(cCR) and were allocated to the OG, six underwent local-excision (LE), and 15 underwent total-mesorectal-excision (TME). The median follow-up duration was 22 (9-42) months. The local-recurrence-rate in the OG was 15.3%, and the LE and TME rates were 16.6% and 0%, respectively. All recurrence cases were salvaged through either LE or TME. The-distant-metastasis rate was 5.1%, 16.6%, and 12.5% in the OG, LE, and TME groups, respectively. The endoscopic negative-predictive-value(NPV) was 50%, and the positive-predictive-value(PPV) was 76.9% in the surgery group (LE + TME). MRI; NPV-50%, PPV-76.9%. PET/CT; NPV-100%, PPV-93.3%. Six patients(28.57%) from surgery group achieved complete pathological response (cPR).

CONCLUSION

Our results indicated a high proportion of selected-rectal-cancers with-cCR after neo-adjuvant-therapy could potentially be managed non-operatively, and major surgery may be avoided.

Clinical and molecular diagnosis of pathologic complete response in rectal cancer: an update

INTRODUCTION

The standard of care for locally advanced rectal cancer includes neoadjuvant chemoradiation with subsequent total mesorectal excision. This approach has shown various degrees of response to neoadjuvant chemoradiation (ranging from complete response to further tumor growth), which have substantial prognostic and therapeutic implications. A total regression of the tumor is a predictor of superior oncologic outcomes compared with partial responders and non-responders. Further, this concept has opened the possibility of nonoperative strategies for complete responders and explains the widespread research interest in finding clinical, radiographic, pathologic, and biochemical parameters that allow for identification of these patients. Areas covered: The present review evaluates the most recent efforts in the literature to identify predictors of patients likely to achieve a complete response following neoadjuvant treatment for the management of rectal cancer. This includes clinical predictors of pathologic complete response such as tumor location, size, and stage, molecular predictors such as tumor biology and microRNA, serum biomarkers such as carcinoembryogenic antigen and nomograms. Expert commentary: There has been significant progress in our ability to predict pathological complete response. However, more high-quality research is still needed to use this concept to confidently dictate clinical management.

Value of FDG-PET/CT Volumetry After Chemoradiotherapy in Rectal Cancer

BACKGROUND

Neoadjuvant chemoradiotherapy followed by an optimal surgery is the standard treatment for patients with locally advanced rectal cancer. FDG-PET/CT is commonly used as the modality for assessing the effect of chemoradiotherapy.

OBJECTIVE

The purpose of this study was to investigate whether PET/CT-based volumetry could contribute to the prediction of pathological complete response or prognosis after neoadjuvant chemoradiotherapy.

DESIGN

This was a retrospective cohort study.

SETTINGS

This study was conducted at a single research center.

PATIENTS

Ninety-one consecutive patients with locally advanced rectal cancer were enrolled between January 2005 and December 2015.

INTERVENTION

Patients underwent PET/CT before and after neoadjuvant chemoradiotherapy.

MAIN OUTCOME MEASURES

Maximum standardized uptake value and total lesion glycolysis on PET/CT before and after neoadjuvant chemoradiotherapy were calculated using isocontour methods. Correlations between these variables and clinicopathological factors and prognosis were assessed.

RESULTS

PET/CT-associated variables before chemoradiotherapy were not correlated with either clinicopathological factors or prognosis. Maximum standardized uptake value was associated with pathological complete response, but total lesion glycolysis was not. Maximum standardized uptake value correlated with ypT, whereas total lesion glycolysis correlated with both ypT and ypN. High total lesion glycolysis was associated with a considerably poorer prognosis; the 5-year recurrence rate was 65% and the 5-year mortality rate 42%, whereas in lesions with low total lesion glycolysis, these were 6% and 2%. On multivariate analysis, high total lesion glycolysis was an independent risk factor for recurrence (HR = 4.718; p = 0.04).

LIMITATIONS

The gain in fluoro-2-deoxy-D-glucose uptake may differ between scanners, thus the general applicability of this threshold should be validated.

CONCLUSIONS

In patients with locally advanced rectal cancer, high total lesion glycolysis after neoadjuvant chemoradiotherapy is strongly associated with a worse prognosis. Total lesion glycolysis after chemoradiotherapy may be a promising preoperative predictor of recurrence and death. See Video Abstract at http://links.lww.com/DCR/A464.

Magnetic Resonance Imaging Evaluation in Neoadjuvant Therapy of Locally Advanced Rectal Cancer: A Systematic Review

Background

The aim of the study was to present an update concerning several imaging modalities in diagnosis, staging and pre-surgery treatment response assessment in locally advanced rectal cancer (LARC). Modalities include: traditional morphological magnetic resonance imaging (MRI), functional MRI such as dynamic contrast enhanced MRI (DCE-MRI) and diffusion weighted imaging (DWI). A systematic review about the diagnostic accuracy in neoadjuvant therapy response assessment of MRI, DCE-MRI, DWI and Positron Emission Tomography/Computed Tomography (PET/CT) has been also reported.

Methods

Several electronic databases were searched including PubMed, Scopus, Web of Science, and Google Scholar. All the studies included in this review reported findings about therapy response assessment in LARC by means of MRI, DCE-MRI, DWI and PET/CT with details about diagnostic accuracy, true and false negatives, true and false positives. Forest plot and receiver operating characteristic (ROC) curves analysis were performed. Risk of bias and the applicability at study level were calculated.

Results

Twenty-five papers were identified. ROC curves analysis demonstrated that multimodal imaging integrating morphological and functional MRI features had the best accuracy both in term of sensitivity and specificity to evaluate preoperative therapy response in LARC. DCE-MRI following to PET/CT showed high diagnostic accuracy and their results are also more reliable than conventional MRI and DWI alone.

Conclusions

Morphological MRI is the modality of choice for rectal cancer staging permitting a correct assessment of the disease extent, of the lymph node involvement, of the mesorectal fascia and of the sphincter complex for surgical planning. Multimodal imaging and functional DCE-MRI may also help in the assessment of treatment response allowing to guide the surgeon versus conservative strategies and/or tailored approach such as “wait and see” policy.

FDG PET/CT Can Assess the Response of Locally Advanced Rectal Cancer to Neoadjuvant Chemoradiotherapy: Evidence From Meta-analysis and Systematic Review

INTRODUCTION

Neoadjuvant chemoradiotherapy (CRT) is indicated in locally advanced rectal adenocarcinoma where there is a high risk of local recurrence based on preoperative imaging. Optimal radiological assessment of CRT response is unknown, and metabolic assessment of the tumor has been suggested to gauge response before surgical resection.

PATIENTS AND METHODS

A systematic search of the MEDLINE database was performed using the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) statement to identify papers comparing pre- and post-CRT PET/CT in patients with locally advanced rectal adenocarcinoma with histopathological assessment of tumor regression. Papers were assessed with the QUADAS (Quality Assessment of Diagnostic Accuracy Studies) tool. Meta-analysis was performed for response index (RI) and SUVmax post-CRT.

RESULTS

Ten of 69 studies met inclusion criteria containing a total of 538 patients. Methodological quality was high with low heterogeneity. In all studies, post-CRT PET/CT showed a reduction in SUVmax and the RI irrespective of histological findings. Tumors confirmed to have regressed after CRT had a mean difference of 12.21% higher RI (95% confidence interval, 6.51-17.91; P < 0.00001) compared with nonresponders. Mean difference between pre- and post-CRT SUVmax groups was -2.48 (95% confidence interval, -3.06 to -1.89; P < 0.00001) with histopathological responders having a lower post-CRT SUVmax.

CONCLUSIONS

The available evidence suggests that PET/CT may be a useful addition to the current imaging modalities in the assessment of treatment response.

Circulating serum microRNA-345 correlates with unfavorable pathological response to preoperative chemoradiotherapy in locally advanced rectal cancer

Preoperative chemoradiotherapy (pre-CRT) has been represented as the standard treatment for locally advanced rectal cancer (LARC), but large variations of tumor radiation response to CRT have been reported in the clinic. To explore the function of microRNAs as potential therapeutic predictors of pre-CRT pathological response in LARC, we analyzed global miRNA expression in CRT-sensitive and CRT-resistant groups before treatment. MiR-345 was significantly elevated in the CRT-resistant group. Therefore, miR-345 was selected as a candidate for further analysis. We assessed the correlation between the miRNA signatures and the chemoradiotherapeutic response in 20 randomly selected LARC tissue samples (Validation set) and 87 serum samples (Training set) by qRT-PCR. Further, we validated the results in 42 randomly selected LARC serum samples (Validation set). High miR-345 expression was significantly correlated with unfavorable pre-CRT pathological response in tissue and serum. Moreover, low miR-345 levels predicted superior 3-year local recurrence free survival (LRFS). Taken together, circulating serum miR-345 correlates with unfavorable pre-CRT response and poor locoregional control in LARC. It might be a promising biomarker to facilitate patient stratification for personalized treatment.

Early 18F-FDG PET/CT Evaluation Shows Heterogeneous Metabolic Responses to Anti-EGFR Therapy in Patients with Metastatic Colorectal Cancer

OBJECTIVE

The aim of this pilot study was to explore intrapatient mixed metabolic response and early 18F-FDG PET response evaluation using predefined quantification strategies in patients with advanced KRAS wild-type colorectal adenocarcinoma (mCRC) treated with cetuximab.

METHODS

A 18F-FDG PET was performed at baseline and after 2 cycles of cetuximab. Metabolic response was categorized using thresholds suggested in PERCIST. Quantitative analysis was done for the sum of all target lesions, ≤ 5 lesions and the metabolically most active lesion per PET. Quantitative data were correlated with clinical benefit, according to RECIST v1.1, after two months of treatment.

RESULTS

In nine evaluable patients the total number of target lesions was 34 (1-8 per patient). Mixed metabolic response was observed in three out of seven patients with multiple target lesions, using TLG. Dichotomised metabolic data of the sum of all or ≤ 5 lesions had a concordance with clinical benefit of 89% using SULmax or SULpeak, and 100% using TLG. Evaluating the metabolically most active lesion, concordance was 89% for all three units. Additionally, the decrease in TLG was significantly correlated with PFS for all three quantification strategies.

CONCLUSION

Mixed metabolic response was observed in nearly half of the patients with advanced KRAS wild-type mCRC treated with cetuximab. If ≤ 5 target lesions were evaluated using TLG clinical benefit was predicted correctly for all patients. Moreover, decrease in TLG is significantly correlated with the duration of PFS. Validation of these promising preliminary results in a larger cohort is currently on-going.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01691391.

Relationship between the Temporal Changes in Positron-Emission-Tomography-Imaging-Based Textural Features and Pathologic Response and Survival in Esophageal Cancer Patients

PURPOSE

Although change in standardized uptake value (SUV) measures and PET-based textural features during treatment have shown promise in tumor response prediction, it is unclear which quantitative measure is the most predictive. We compared the relationship between PET-based features and pathologic response and overall survival with the SUV measures in esophageal cancer.

METHODS

Fifty-four esophageal cancer patients received PET/CT scans before and after chemoradiotherapy. Of these, 45 patients underwent surgery and were classified into complete, partial, and non-responders to the preoperative chemoradiation. SUVmax and SUVmean, two cooccurrence matrix (Entropy and Homogeneity), two run-length matrix (RLM) (high-gray-run emphasis and Short-run high-gray-run emphasis), and two size-zone matrix (high-gray-zone emphasis and short-zone high-gray emphasis) textures were computed. The relationship between the relative difference of each measure at different treatment time points and the pathologic response and overall survival was assessed using the area under the receiver-operating-characteristic curve (AUC) and Kaplan-Meier statistics, respectively.

RESULTS

All Textures, except Homogeneity, were better related to pathologic response than SUVmax and SUVmean. Entropy was found to significantly distinguish non-responders from the complete (AUC = 0.79, p = 1.7 × 10(-4)) and partial (AUC = 0.71, p = 0.01) responders. Non-responders can also be significantly differentiated from partial and complete responders by the change in the run-length and size-zone matrix textures (AUC = 0.71-0.76, p ≤ 0.02). Homogeneity, SUVmax, and SUVmean failed to differentiate between any of the responders (AUC = 0.50-0.57, p ≥ 0.46). However, none of the measures were found to significantly distinguish between complete and partial responders with AUC <0.60 (p = 0.37). Median Entropy and RLM textures significantly discriminated patients with good and poor survival (log-rank p < 0.02), while all other textures and survival were poorly related (log-rank p > 0.25).

CONCLUSION

For the patients studied, temporal changes in Entropy and all RLM were better correlated with pathological response and survival than the SUV measures. The hypothesis that these metrics can be used as clinical predictors of better patient outcomes will be tested in a larger patient dataset in the future.

Combined value of apparent diffusion coefficient-standardized uptake value max in evaluation of post-treated locally advanced rectal cancer

AIM: To assess the clinical diagnostic value of functional imaging, combining quantitative parameters of apparent diffusion coefficient (ADC) and standardized uptake value (SUV)max, before and after chemo-radiation therapy, in prediction of tumor response of patients with rectal cancer, related to tumor regression grade at histology.

METHODS: A total of 31 patients with biopsy proven diagnosis of rectal carcinoma were enrolled in our study. All patients underwent a whole body ¹⁸FDG positron emission tomography (PET)/computed tomography (CT) scan and a pelvic magnetic resonance (MR) examination including diffusion weighted (DW) imaging for staging (PET1, RM1) and after completion (6.6 wk) of neoadjuvant treatment (PET2, RM2). Subsequently all patients underwent total mesorectal excision and the histological results were compared with imaging findings. The MR scanning, performed on 1.5 T magnet (Philips, Achieva), included T2-weighted multiplanar imaging and in addition DW images with b-value of 0 and 1000 mm²/s. On PET/CT the SUVmax of the rectal lesion were calculated in PET1 and PET2. The percentage decrease of SUVmax (ΔSUV) and ADC (ΔADC) values from baseline to presurgical scan were assessed and correlated with pathologic response classified as tumor regression grade (Mandard’s criteria; TRG1 = complete regression, TRG5 = no regression).

RESULTS: After completion of therapy, all the patients were submitted to surgery. According to the Mandard’s criteria, 22 tumors showed complete (TRG1) or subtotal regression (TRG2) and were classified as responders; 9 tumors were classified as non responders (TRG3, 4 and 5). Considering all patients the mean values of SUVmax in PET 1 was higher than the mean value of SUVmax in PET 2 (P < 0.001), whereas the mean ADC values was lower in RM1 than RM2 (P < 0.001), with a ΔSUV and ΔADC respectively of 60.2% and 66.8%. The best predictors for TRG response were SUV2 (threshold of 4.4) and ADC2 (1.29 × 10^-3 mm²/s) with high sensitivity and specificity. Combining in a single analysis both the obtained median value, the positive predictive value, in predicting the different group category response in related to TRG system, presented R² of 0.95.

CONCLUSION: The functional imaging combining ADC and SUVmax in a single analysis permits to detect changes in cellular tissue structures useful for the assessment of tumour response after the neoadjuvant therapy in rectal cancer, increasing the sensitivity in correct depiction of treatment response than either method alone.

Assessing pathological complete response to neoadjuvant chemoradiotherapy in locally advanced rectal cancer: a systematic review

AIM

Pathological complete response to neoadjuvant chemoradiotherapy is found in 20% of patients with rectal cancer undergoing long-course chemoradiotherapy. Some authors have suggested that these patients do not need to undergo surgery and can be managed with careful follow-up, with surgery only used in the event of clinical failure. Widespread adoption of this regimen is limited by the accuracy of methods to confirm a pathological complete response (pCR).

METHOD

A systematic search of PubMed, Medline and Cochrane databases was conducted to identify clinical, histological and radiological features in those patients with rectal cancer who achieved a pCR following chemoradiotherapy. Searches were conducted with the following keywords and MeSH search terms: 'rectal neoplasm', 'response', 'neoadjuvant', 'preoperative chemoradiation' and 'tumour response'. After review of title and abstracts, 89 articles addressing the assessment of pCR were identified.

RESULTS

Histology and clinical assessment are the most effective methods of assessment of pCR, with histology considered the gold standard. Clinical assessment is limited to low rectal tumours and is open to significant inter-rater variability, while histological examination requires a surgical specimen. Diffusion-weighted MRI and (18) F-fluorodeoxyglucose positron emission tomography/CT demonstrate the greatest potential for the assessment of pCR, but both modalities have limited accuracy.

CONCLUSION

Determination of a pCR is crucial if a nonoperative approach is to be undertaken proactively. Various methods are available, but currently they lack sufficient sensitivity and specificity to define management. This is likely to be an area of further research in the future.

The role of diffusion-weighted MRI and (18)F-FDG PET/CT in the prediction of pathologic complete response after radiochemotherapy for rectal cancer: a systematic review

After neoadjuvant radiochemotherapy (RCT) for locally advanced rectal cancer, 15-27% of the patients experience a pathological complete response (pCR). This observation raises the question as to whether invasive surgery could be avoided in a selected cohort of patients who obtain a clinical complete response after preoperative RCT. In this respect, there has been growing interest in functional imaging techniques to improve clinical response assessment. This systematic review focuses on the role of diffusion-weighted imaging (DWI) and (18)F-fluorodeoxyglucose positron emission tomography/computed tomography ((18)F-FDG PET/CT) in the prediction of pCR after RCT for rectal cancer. A total of 14 publications on DWI and 25 on (18)F-FDG PET/CT were retrieved. Pooled analysis of individual patient data shows both imaging modalities have a low positive predictive value in the prediction of pCR (mean PPV of 54% and 39% for DWI- and (18)F-FDG PET/CT-based parameters respectively). Especially pre-RCT imaging is unable to predict pCR with overall accuracies of 68-72% for DWI and 44% for (18)F-FDG PET/CT. Qualitative DWI assessment 5-10weeks after the end of RCT may outperform apparent diffusion coefficient (ADC)-based DWI-parameters (overall accuracy of 87% vs. 74-78%). Although few data are available, early changes in FDG-uptake seem promising in the prediction of pCR and the role of (18)F-FDG PET/CT during RCT should be further investigated. Quantitative and qualitative (18)F-FDG PET/CT measurements are equally effective in the assessment of pCR after RCT. The major strength of DWI and (18)F-FDG PET/CT lies in the identification of non-responders who are not candidates for organ preservation. Up to now, DWI and (18)F-FDG PET/CT are not accurate enough to safely select patients for organ-sparing strategies. Future research must focus on the integration of functional imaging with clinical data and molecular biomarkers.

Evolution of imaging in rectal cancer: multimodality imaging with MDCT, MRI, and PET

Magnetic resonance imaging (MRI), multidetector computed tomography (MDCT), and positron emission tomography (PET) are complementary imaging modalities in the preoperative staging of patients with rectal cancer, and each offers their own individual strengths and weaknesses. MRI is the best available radiologic modality for the local staging of rectal cancers, and can play an important role in accurately distinguishing which patients should receive preoperative chemoradiation prior to total mesorectal excision. Alternatively, both MDCT and PET are considered primary modalities when performing preoperative distant staging, but are limited in their ability to locally stage rectal malignancies. This review details the role of each of these three modalities in rectal cancer staging, and how the three imaging modalities can be used in conjunction.

Pathologic evaluation of the response of mesorectal positive nodes to preoperative chemoradiotherapy in patients with rectal cancer

BACKGROUND

The response of positive mesorectal lymph nodes to chemoradiotherapy remains largely unstudied in patients with rectal cancer. The aim of this study was to investigate the requirements of the total regression of positive nodes treated with chemoradiotherapy.

METHODS

The response of the primary tumor was evaluated according to the tumor regression grade (TRG 0-4) in resected specimens, and positive lymph nodes were assessed according to the lymph node regression grade (LRG 1-3), with TRG 4 and LRG 3 indicating total regression. We investigated the relationships among TRG, LRG, and the sizes of positive lymph nodes.

RESULTS

Among 178 patients, 68 (38.2%) had 200 positive lymph nodes. We first investigated the relationship of positive nodes to TRG and LRG and found that the response of the primary tumor to chemoradiotherapy correlated with the response of positive nodes. Next, we investigated the correlation between LRG and the size of positive nodes. At TRG 1 and 2, LRG score was not correlated with the positive node size. In contrast, at TRG 3, LRG score was correlated with the size of positive nodes. Next, our assessment of the relationship between the sizes of positive nodes and complete degeneration to LRG 3 showed that the most accurate cut-off score on receiver-operator-characteristics curve analysis was 6 mm in maximum diameter for TRG 3.

CONCLUSION

The requirements of the total regression of positive nodes are 1) degeneration of the primary tumor to TRG 3 and 2) a positive node diameter of <6 mm.

Nomogram predicting response after chemoradiotherapy in rectal cancer using sequential PETCT imaging: a multicentric prospective study with external validation

PURPOSE

To develop and externally validate a predictive model for pathologic complete response (pCR) for locally advanced rectal cancer (LARC) based on clinical features and early sequential (18)F-FDG PETCT imaging.

MATERIALS AND METHODS

Prospective data (i.a. THUNDER trial) were used to train (N=112, MAASTRO Clinic) and validate (N=78, Università Cattolica del S. Cuore) the model for pCR (ypT0N0). All patients received long-course chemoradiotherapy (CRT) and surgery. Clinical parameters were age, gender, clinical tumour (cT) stage and clinical nodal (cN) stage. PET parameters were SUVmax, SUVmean, metabolic tumour volume (MTV) and maximal tumour diameter, for which response indices between pre-treatment and intermediate scan were calculated. Using multivariate logistic regression, three probability groups for pCR were defined.

RESULTS

The pCR rates were 21.4% (training) and 23.1% (validation). The selected predictive features for pCR were cT-stage, cN-stage, response index of SUVmean and maximal tumour diameter during treatment. The models' performances (AUC) were 0.78 (training) and 0.70 (validation). The high probability group for pCR resulted in 100% correct predictions for training and 67% for validation. The model is available on the website www.predictcancer.org.

CONCLUSIONS

The developed predictive model for pCR is accurate and externally validated. This model may assist in treatment decisions during CRT to select complete responders for a wait-and-see policy, good responders for extra RT boost and bad responders for additional chemotherapy.

Is diffusion-weighted MRI superior to FDG-PET or FDG-PET/CT in evaluating and predicting pathological response to preoperative neoadjuvant therapy in patients with rectal cancer?

OBJECTIVE

This meta-analysis aimed to compare the diagnostic accuracy of diffusion-weighted magnetic resonance imaging (DW-MRI) and fluorodeoxyglucose-positron emission tomography (FDG-PET) or FDG-PET/computed tomography (CT) in evaluating and predicting pathological response to preoperative neoadjuvant chemoradiotherapy (NCRT) in patients with rectal cancer.

METHODS

A comprehensive literature research was conducted to identify the relevant studies for this meta-analysis. Combined sensitivity, specificity, positive (PPV) and negative predictive values (NPV) were calculated.

RESULTS

A total of 33 studies including 1564 patients met the inclusion criteria. The pooled sensitivity (81% [95% CI 74-86%] vs 85% [95% CI 75-91%]) and NPV (80% [95% CI 68-89%] vs 91% [95% CI 80-95%]) for FDG-PET or FDG-PET/CT were significantly lower than those for DW-MRI (P < 0.05). No differences were observed in pooled specificity and PPV between DW-MRI and FDG-PET or FDG-PET/CT. Further subgroup analyses showed that DW-MRI had higher sensitivity on adenocarcinomas alone than on those including mucinous-type adenocarcinomas (92% [95% CI 83-99%] vs 76% [95% CI 63-90%], P = 0.00).

CONCLUSIONS

DW-MRI is superior to FDG-PET or FDG-PET/CT in predicting and evaluating pathological responses to preoperative NCRT in patients with rectal cancer. However, its relatively low specificity and PPV limit its application in clinic, making it currently inappropriate to monitor such patients, especially those with mucinous-type rectal adenocarcinomas.

Tumor SUVmax Normalized to Liver Uptake on (18)F-FDG PET/CT Predicts the Pathologic Complete Response After Neoadjuvant Chemoradiotherapy in Locally Advanced Rectal Cancer

PURPOSE

This study investigates the feasibility of using (18)F-fluorodeoxyglucose positron emission tomography/computed tomography ((18)F-FDG PET/CT) to predict the pCR (pathologic complete response) rate after neoadjuvant chemoradiotherapy (NCRT) in patients with locally advanced rectal cancer.

METHODS

A total of 88 patients with locally advanced rectal cancer were retrospectively analyzed. All patients were treated with NCRT, followed by radical surgery, and (18)F-FDG PET/CT was performed before and after NCRT. For a semiquantitative assessment, a volume of interest was drawn, including the whole tumor region, and the maximum SUV (SUVmax), SUVmax normalized to liver uptake (SLR), SUVmax normalized to blood pool uptake (SBR), the metabolic tumor volume at SUV 2.0 (MTV[2.0]), SUV 2.5 (MTV[2.5]), and SUV 3.0 (MTV[3.0]) were measured. In addition, their percentage changes after NCRT were assessed. The pCR was verified through a histologic examination of postsurgical specimens. A receiver operating characteristic curve analysis was conducted to predict the pCR by using these PET parameters.

RESULTS

The pCR was predicted in 17 patients (19 %). The values of the area under the curve (AUC) for predicting the pCR were 0.774 for SUVmax after NCRT, 0.826 for SLR after NCRT, 0.815 for SBR after NCRT, 0.724 for MTV(2.5) after NCRT, 0.729 for the percentage change in SUVmax, 0.700 for the percentage change in SLR, and 0.749 for the percentage change in MTV (2.5). Among these PET parameters, SLR after NCRT showed the highest AUC value. The optimal criterion, sensitivity, specificity, and accuracy of SLR after NCRT for predicting the pCR were ≤1.41, 88 %, 65 %, and 68 %, respectively.

CONCLUSIONS

F-FDG PET was found to be useful for predicting the pCR after NCRT in patients with locally advanced rectal cancer. Among various PET parameters, SUVmax normalized to liver uptake after NCRT was the best predictor of the pCR.

18F-FDG PET predicts pathological response to preoperative chemoradiotherapy in patients with primary rectal cancer: a meta-analysis

OBJECTIVE

The aim of this study was to assess the performance of fluorine-18-fluorodeoxyglucose (18F-FDG) positron emission tomography (PET) in predicting pathological response to preoperative chemoradiotherapy (CRT) in patients with primary rectal cancer.

METHODS

Potentially relevant articles were searched in the databases of PubMed and Embase from January 1990 to September 2013. The Quality Assessment for Diagnostic Accuracy Studies criteria was employed to assess the quality of all of the included studies. The pooled sensitivity and specificity were calculated, and the area under the curve of the summary receiver operating characteristic curve was obtained. Subgroup analysis was conducted to explore the sources of heterogeneity.

RESULTS

Thirty-one eligible studies involving 1527 patients were ultimately included in the meta-analysis. Four main quantitative or qualitative parameters [response index (RI), post-treatment maximum standardized uptake value (SUVmax-post), visual response (VR) and the percentage change in total lesion glycolysis (TLG) before and after CRT (deltaTLG%)] related to PET or positron emission tomography/computed tomography (PET/CT) were assessed for the prediction of histopathological response. The pooled sensitivities of these four parameters were comparable and were 74, 74, 75 and 78%, respectively (P>0.05). The pooled specificity of deltaTLG% was higher than that of the other three parameters (RI, SUVmax-post and VR) and was 81, 66, 64 and 67%, respectively (P<0.05). The results from subgroup analysis showed that the RI and SUVmax-post had higher specificity in predicting tumor regression grade (TRG) than complete pathological response (pCR) [RI, 71 vs. 59% (P=0.0275); SUVmax-post, 72 vs. 61% (P=0.0178)].The diagnostic sensitivity and specificity of the RI and SUVmax-post when the post-treatment PET or PET/CT scan was performed at two different time points (during CRT and after the completion of CRT) were 82 vs. 72% (P=0.0630) and 78 vs. 63% (P=0.0059), respectively.

CONCLUSIONS

18F-FDG PET could be a potentially powerful non-invasive tool for predicting pathological response; the related parameters RI and SUVmax-post may be more suitable for the prediction of TRG than pCR. The current data also suggested that the optimum post-treatment 18F-FDG PET scan could be carried out during CRT.