Long-term prognostic value of 18F-FDG PET in patients with locally advanced rectal cancer previously treated with neoadjuvant radiochemotherapy

Unanticipated pathological clearance in two cases of clinical T4b dMMR/MSI-h advanced colorectal cancer: the potential of immune checkpoint inhibitors despite positive positron-emission tomography results

BACKGROUND

The standard treatment for colorectal cancer consists of surgery and chemotherapy, which can be combined to improve outcomes. Immune checkpoint inhibitors (ICI) are a significant advancement in the standard treatment of metastatic, unresectable colorectal cancer with deficient mismatch repair (dMMR). However, limited data are available about the use of ICI in the neoadjuvant and conversion settings. Here, we present two cases treated with ICI.

CASE PRESENTATION

Case 1: A 75-year-old male with a large, borderline resectable rectal cancer diagnosed as cT4bN1bM0 who underwent neoadjuvant chemotherapy, followed by combination ICI consisting of ipilimumab and nivolumab. After four courses of ICI, the tumor significantly shrank, but positron emission tomography still showed a positive result and R0 resection was performed. Pathological analysis revealed no residual cancer cells. The patient has been monitored without adjuvant chemotherapy, and no recurrences have occurred after one year. Case 2: A 60-year-old male with locally advanced sigmoid colon cancer who received neoadjuvant treatment with pembrolizumab. The tumor partially shrank after three courses, and continued pembrolizumab monotherapy resulted in further tumor shrinkage which still showed positive positron emission tomography. Curative sigmoidectomy with partial resection of the ileum and bladder was performed, and the pathological outcome was pCR. There was no viable tumor in the specimen. The patient has been monitored without adjuvant chemotherapy for six months, and no recurrence has been observed.

CONCLUSIONS

The present study reports two cases, including a large, borderline resectable rectal cancer after failure of chemotherapy followed by combination treatment with nivolumab and ipilimumab and one case of sigmoid colon cancer after pembrolizumab treatment, which resulted in pathological complete response. However, it remains unknown whether ICI therapy can replace surgery or diminish the optimal extent of resection, or whether adjuvant chemotherapy is needed after surgery in the case of achieving pCR after ICI therapy. Overall, this case report suggests that ICI before colorectal surgery can be effective and potentially a 'watch-and-wait" strategy could be used for cases in which ICI is effective.

FDG-PET/MRI for Nonoperative Management of Rectal Cancer: A Prospective Pilot Study

Nonoperative management (NOM) is increasingly utilized for rectal cancer patients with a clinical complete response (cCR) following total neoadjuvant therapy (TNT). The objective of this pilot study was to determine whether FDG-PET/MRI alters clinical response assessments among stage I-III rectal cancer patients undergoing TNT followed by NOM, relative to MRI alone. This prospective study included 14 subjects with new rectal cancer diagnoses. Imaging consisted of FDG-PET/MRI for initial staging, post-TNT restaging, and surveillance during NOM. Two independent readers assessed treatment response on MRI followed by FDG-PET/MRI. Inter-reader differences were resolved by consensus review. The reference standard for post-TNT restaging consisted of surgical pathology or clinical follow-up. 7/14 subjects completed post-TNT restaging FDG-PET/MRIs. 5/7 subjects had evidence of residual disease and underwent total mesorectal excision; 2/7 subjects had initial cCR with no evidence of disease after 12 months of NOM. FDG-PET/MRI assessments of cCR status at post-TNT restaging had an accuracy of 100%, compared with 71% for MRI alone, as FDG-PET detected residual tumor in 2 more subjects. Inter-reader agreement for cCR status on FDG-PET/MRI was moderate (kappa, 0.56). FDG-PET provided added value in 82% (9/11) of restaging/surveillance scans. Our preliminary data indicate that FDG-PET/MRI can detect more residual disease after TNT than MRI alone, with the FDG-PET component providing added value in most restaging/surveillance scans.

The role of MRI and 18F-FDG PET/CT with respect to evaluation of pathological response in the rectal cancer patients after neoadjuvant chemoradiotherapy

BACKGROUND

We aimed to evaluate the role of magnetic resonance imaging (MRI) and 18F-fluorodeoxyglucose (FDG) positron emission tomography-computed tomography (PET-CT) in determining the correct stage and predicting the pathological response.

METHODS

Seventy one patients with pathologic proven rectal adenocarcinoma, clinical stage IIA-IVA, and neoadjuvant chemoradiotherapy (CRT) were evaluated retrospectively. Radiotherapy was delivered 45-50 Gy in 25 fractions with concomitant oral capecitabine. Pelvic MRI, colonoscopy, and 18F-FDG PET-CT were performed before the neoadjuvant treatment (NAT). After NAT, MRI and PET-CT were performed for re-evaluation.

RESULTS

The median follow-up time was 25 months (range: 3-57 months). Of the 71 patients who underwent NAT, 57 patients underwent surgery. Downstaging was recorded in 48 (84.2%) of 57 patients who underwent surgery. There was no statistically significant difference between both MRI and PET-CT with pathology results in terms of response evaluation. As a result of the comparison of MRI and PET-CT with pathological results; sensitivity and specificity were 91.6% (44/48) and 22.2% (2/9) for MRI, and 100% (47/47) and 12.5% (1/8) for PET-CT, respectively.

CONCLUSION

PET-CT and MRI are effective in predicting response to NAT and predictive for the pathological response. A more accurate response can be judged when both PET-CT and MRI are executed together in restaging after NAT.

Association of visual and quantitative heterogeneity of 18F-FDG PET images with treatment response in locally advanced rectal cancer: A feasibility study

BACKGROUND AND PURPOSE

Few tools are available to predict tumor response to treatment. This retrospective study assesses visual and automatic heterogeneity from 18F-FDG PET images as predictors of response in locally advanced rectal cancer.

METHODS

This study included 37 LARC patients who underwent an 18F-FDG PET before their neoadjuvant therapy. One expert segmented the tumor from the PET images. Blinded to the patient´s outcome, two experts established by consensus a visual score for tumor heterogeneity. Metabolic and texture parameters were extracted from the tumor area. Multivariate binary logistic regression with cross-validation was used to estimate the clinical relevance of these features. Area under the ROC Curve (AUC) of each model was evaluated. Histopathological tumor regression grade was the ground-truth.

RESULTS

Standard metabolic parameters could discriminate 50.1% of responders (AUC = 0.685). Visual heterogeneity classification showed correct assessment of the response in 75.4% of the sample (AUC = 0.759). Automatic quantitative evaluation of heterogeneity achieved a similar predictive capacity (73.1%, AUC = 0.815).

CONCLUSION

A response prediction model in LARC based on tumor heterogeneity (assessed either visually or with automatic texture measurement) shows that texture features may complement the information provided by the metabolic parameters and increase prediction accuracy.

Impact of PET/CT for Restaging Patients With Locally Advanced Rectal Cancer After Neoadjuvant Chemoradiation

BACKGROUND

A major challenge in identifying candidates for nonoperative management of locally advanced rectal cancer is predicting pathologic complete response (pCR) following chemoradiation. We evaluated pre- and post-CRT PET-CT imaging to predict pCR and prognosis in this set of patients undergoing resection after neoadjuvant therapy.

METHODS

We retrospectively identified patients from 2002 to 2015 with locally advanced rectal cancer who underwent CRT, pre- and post-CRT PET-CT imaging, and resection. Univariate and multivariate analysis was performed and receiver operating characteristic (ROC) curves were generated to evaluate the association of PET-CT characteristics with pCR and survival. ROC curves were generated to define optimal cutoff points for predictive PET-CT characteristics.

RESULTS

125 patients were included. pCR rate was 28%, and follow-up was 48 mo. On multivariable analysis, patients who had a pCR had lower median post-CRT maximal standardized uptake value (SUV_max) (3.2 versus 5.2, P = 0.009) and higher median %SUV decrease (72 versus 58%, P = 0.009). ROC curves were generated for %SUV_max decrease (AUC = 0.70) and post-CRT SUV (AUC = 0.69). Post-CRT SUV_max <4.3 and %SUV_max decrease of >66% were equally predictive of pCR with a sensitivity of 65%, specificity of 72%, PPV of 44%, and NPV of 86%. Median 5-y overall and relapse-free survival were improved for patients with post-CRT SUV <4.3 (OS: 86 versus 66%, P = 0.01; RFS: 75 versus 52%, P = 0.01) or %SUV decrease of >66% (OS, 82 versus 66%, P = 0.05; RFS, 75 versus 54%, P = 0.01).

CONCLUSIONS

PET/CT may be useful in identifying patients who did not achieve pCR, as well as overall survival in patients undergoing CRT for rectal cancer. Patients with a post-CRT SUV of >4.3 should be considered for operative management, as an estimated 86% of these patients will not have a pCR.

Early Imaging Biomarker of Myocardial Glucose Adaptations in High-Fat-Diet-Induced Insulin Resistance Model by Using 18F-FDG PET and [U-13C]glucose Nuclear Magnetic Resonance Tracer

Background

High-fat diet (HFD) induces systemic insulin resistance leading to myocardial dysfunction. We aim to characterize the early adaptations of myocardial glucose utility to HFD-induced insulin resistance.

Methods

Male Sprague–Dawley rats were assigned into two groups, fed a regular chow diet or HFD ad libitum for 10 weeks. We used in vivo imaging of cardiac magnetic resonance (CMR), ¹⁸F-FDG PET, and ex vivo nuclear magnetic resonance (NMR) metabolomic analysis for the carbon-13-labeled glucose ([U-¹³C]Glc) perfused myocardium.

Results

As compared with controls, HFD rats had a higher ejection fraction and a smaller left ventricular end-systolic volume (P < 0.05), with SUV_max of myocardium on ¹⁸F-FDG PET significantly increased in 4 weeks (P < 0.005). The [U-¹³C]Glc probed the increased glucose uptake being metabolized into pyruvate and acetyl-CoA, undergoing oxidative phosphorylation via the tricarboxylic acid (TCA) cycle, and then synthesized into glutamic acid and glutamine, associated with overexpressed LC3B (P < 0.05).

Conclusions

HFD-induced IR associated with increased glucose utility undergoing oxidative phosphorylation via the TCA cycle in the myocardium is supported by overexpression of glucose transporter, acetyl-CoA synthase. Noninvasive imaging biomarker has potentials in detecting the metabolic perturbations prior to the decline of the left ventricular function.

Status for clinically complete remission rectal cancer after concomitant chemo-radiotherapy in Taiwan

Treatment for Rectal cancer changed after the induction of concomitant chemo-radiotherapy, CCRT. Complete remission of the tumor leads to debate of the necessity of surgical intervention. We evaluate the treatment outcome to know if operation is beneficial to these patients. Patients received long course concomitant chemo-radiotherapy for advanced rectal cancer between 2004 and 2013 in Taiwan were enrolled. Total 2780 patients diagnosed advanced rectal cancer were enrolled. In these patients, 2578 received surgical intervention and 202 were in wait and see for complete remission tumor. Higher local recurrence rate was found with wait and see group (8.9% vs. 2.7%). Also, better overall survival, disease free survival and local recurrence free survival were seen with the surgical intervention group. Surgical intervention may be benefit for some misdiagnosed completed response to CCRT.

PET/CT with Fluorodeoxyglucose During Neoadjuvant Chemoradiotherapy in Locally Advanced Rectal Cancer

Objective

The aim of the present study is to evaluate the accuracy of Positron Emission Tomography/Computed Tomography (PET/CT) with Fluorodeoxyglucose ([18F]FDG) to predict treatment response in patients with locally advanced rectal cancer (LARC) during neoadjuvant chemoradiotherapy.

Patients and methods

Forty-one LARC patients performed [18F]FDG-PET/CT at baseline (PET0). All patients received continuous capecitabine concomitant to radiotherapy on the pelvis, followed by intermittent capecitabine until two weeks before curative surgery. [18F]FDG-PET/CT was also carried out at 40 Gy-time (PET1) and at the end of neoadjuvant therapy (PET2). PET imaging was analysed semi-quantitatively through the measurement of maximal standardised uptake value (SUVmax) and the tumour volume (TV). Histology was expressed through pTNM and Dworak tumor regression grading. Patients were categorised into responder (downstaging or downsizing) and non-responder (stable or progressive disease by comparison pretreatment parameters with clinical/pathological characteristics posttreatment/after surgery).

Logistic regression was used to evaluate SUVmax and TV absolute and percent reduction as predictors of response rate using gender, age, and CEA as covariates. Progression-free survival (PFS) and overall survival (OS) were estimated by the Kaplan-Meier method. Survivals were compared by the Log-Rank test.

Results

Twenty-three responders (9 ypCR, 14 with downstaged disease) and 18 non-responders showed differences in terms of both early and posttreatment SUVmax percent reduction (median comparison: responder = 63.2%, non-responder = 44.2%, p = 0.04 and responder = 76.9%, non-responder = 61.6%, p = 0.06 respectively). The best predictive cut-offs of treatment response for early and posttreatment SUVmax percent reduction were ≥57% and ≥66% from baseline (p = 0.02 and p = 0.01 respectively).

Conclusions

[18F]FDG-PET/CT is a reliable technique for evaluating therapy response during neoadjuvant treatment in LARC, through a categorical classification of the SUV max reduction during treatment.

Predictive value of repeated F-18 FDG PET/CT parameters changes during preoperative chemoradiotherapy to predict pathologic response and overall survival in locally advanced esophageal adenocarcinoma patients

INTRODUCTION

The goal of the current study was to investigate the predictive and prognostic values of repeated F-18 FDG PET/CT parameter changes for prediction of complete pathologic response (pCR) in patients with adenocarcinoma of locally advanced esophageal cancer (LAEC) who received preoperative concurrent chemoradiotherapy (PCRT).

METHODS

A total 53 patients with LAEC patients were included in the current study. All patients were evaluated by F-18 FDG PET/CT before and during chemoradiotherapy. The percent changes (∆, %) in F-18 FDG PET/CT parameters were used to predict pCR and to calculate overall survival (OS). The predictive value for pCR of F-18 FDG PET/CT cutoff values was determined by ROC analysis. The prognostic significance was assessed using Kaplan-Meier analysis.

RESULTS

pCR occurred in 15 patients (28.3 %). When ΔSUVmax > 23.5 % was used as cutoff, the sensitivity and specificity of F-18 FDG PET/CT for prediction of pCR were 100 % and 52.6, respectively. The AUC was 0.750 (95 % CI; 0.612-0.859), and standard error (SE) was 0.0633 (p = 0.0002). ΔMTV resulted in 80 % sensitivity, 76.3 % specificity, and 0.731 AUC (95 % CI; 0.591-0.843, SE = 0.077, p = 0.0027) for cutoff values >25.5 %. When ΔTLG > 44.8 % was used as cutoff, the sensitivity and specificity of F-18 FDG PET/CT for prediction of pCR were 100 and 65.8 %, respectively. The AUC was 0.893 (95 % CI; 0.777-0.961), and SE was 0.0431 (p < 0.0001). Kaplan-Meier analysis showed that high ΔSUVmax, ΔMTV, and ΔTLG were associated with improved OS.

CONCLUSION

In conclusion, the current study shows the capability of the changes (Δ) in repeated F-18 FDG PET/CT parameters to predict the achievement of pCR during PCRT in LAEC patients. Among the parameters, the ΔSUVmax, ΔMTV, and ΔTLG were predictors for pCR and well associated with OS.

Role of fluorine 18 fluorodeoxyglucose positron emission tomography/computed tomography in gastrointestinal cancers

Fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) has become a routine imaging modality for many malignancies and its use is currently increasing. In the present review article, we will summarize the evidence for FDG-PET/CT use in digestive cancers (excluding neuroendocrine tumours), and review the existing recommendations. While PET/CT is nowadays considered to be an important tool in the initial workup of oesophageal and anal cancers, new data are emerging regarding its use in assessing therapeutic efficacy, radiotherapy treatment planning, and detection of recurrence in case of isolated tumour marker elevation. Moreover, PET/CT may help decision making by detecting distant metastatic sites especially in potentially resectable metastatic colorectal cancer and, to a lesser extent, in localized gastric and pancreatic cancers. Finally, incidental focal colonic FDG uptakes require exploration by colonoscopy, as they are often associated with premalignant or malignant lesions.

The value of liver-based standardized uptake value and other quantitative 18F-FDG PET-CT parameters in neoadjuvant therapy response in patients with locally advanced rectal cancer: correlation with histopathology

AIM

We aimed to investigate the value of PET-CT in therapy response and the correlation of quantitative PET parameters with histopathologic results in patients with locally advanced rectal cancer (LARC) before and after neoadjuvant chemoradiotherapy. We also analyzed the correlation of PET-CT parameters between Ki-67 and glucose transporter 1 (GLUT1).

PATIENTS AND METHODS

A total of 29 patients diagnosed with LARC who had undergone a biopsy between 2009 and 2012 were included in our study. Quantitative PET parameters [standardized uptake value (SUV)max-mean, lean body mass SUV(max-mean), tumor/liver SUV, retention index , and [INCREMENT]SUV(max)] were measured before and after therapy using PET-CT. Tumor regression grade (TRG) was evaluated according to Wheeler's classification. Patients in grade 1 were considered responders, whereas patients at grades 2 and 3 were considered nonresponders. Immunohistochemical staining with Ki-67 and GLUT1 was performed on biopsy and surgical specimens. The correlation between staining ratios and SUV was also investigated.

RESULTS

SUV parameters were significantly decreased after therapy (P < 0.001). Twelve (41%) patients were at TRG1, 10 (35%) were at TRG2, and seven (24%) were at TRG3. A cutoff SUV(max) of 5.05 to discriminate between responders and nonresponders after treatment revealed a sensitivity of 57%, specificity of 73%, negative predictive value of 65%, positive predictive value of 67%, and accuracy of 66%. Using a cutoff of 3.55 for the SUV(mean) (standardized measurement of SUV with 1.2-cm-diameter region of interest) revealed a sensitivity, specificity, negative predictive value, positive predictive value, and accuracy of 67, 76, 67, 76, and 72%, respectively. For a cutoff of 1.95 for the tumor SUV(mean)/liver SUV(mean), these diagnostic values after therapy were 73, 78, 82, 67, and 76%, respectively. We found a moderate correlation between liver-based SUV(max) (r = -0.35, P = 0.019) and SUV(mean )(r = -0.31, P = 0.036) with GLUT1 after therapy. Quantitative PET parameters and retention index were moderately correlated with Ki-67.

CONCLUSION

PET-CT is a useful method for assessing the response to neoadjuvant chemoradiotherapy in patients with LARC. The most significant parameter for assessing treatment response using SUV parameters is the tumor/liver ratio.

Multidisciplinary treatment of rectal cancer in 2014: Where are we going?

In the present review we discuss the recent developments and future directions in the multimodal treatment of locally advanced rectal cancer, with respect to staging and re-staging modalities, to the current role of neoadjuvant chemo-radiation and to the conservative and more limited surgical approaches based on tumour response after neoadjuvant combined therapy. When initial tumor staging is considered a high accuracy has been reported for T pre-treatment staging, while preoperative lymph node mapping is still suboptimal. With respect to tumour re-staging, all the current available modalities still present a limited accuracy, in particular in defining a complete response. The role of short vs long-course radiotherapy regimens as well as the optimal time of surgery are still unclear and under investigation by means of ongoing randomized trials. Observational management or local excision following tumour complete response are promising alternatives to total mesorectal excision, but need further evaluation, and their use outside of a clinical trial is not recommended. The preoperative selection of patients who will benefit from neoadjuvant radiotherapy or not, as well as the proper identification of a clinical complete tumour response after combined treatment modalities,will influence the future directions in the treatment of locally advanced rectal cancer.

Early prediction of response by ¹⁸F-FDG PET/CT during preoperative therapy in locally advanced rectal cancer: a systematic review

AIM

To assess the predictive value of fluorine-18-fluorodeoxyglucose ((18)F-FDG) positron emission tomography/computed tomography (PET/CT) in early assessing response during neo-adjuvant chemoradiotherapy (CRT) in patients with locally advanced rectal cancer.

MATERIALS AND METHODS

A systematic review was performed by search of MEDLINE Library for the following terms: "rectal carcinoma OR rectal cancer", "predictive OR prediction OR response assessment OR response OR assessment", "early OR ad interim", "therapy", "FDG OR (18)F-FDG", "PET OR PET/CT". Articles performed by the use of stand-alone PET scanners were excluded.

RESULTS

10 studies met the inclusion criteria, including 302 patients. PET/CT demonstrated a good early predictive value in the global cohort (mean sensitivity = 79%; mean specificity = 78%). SUV and its percentage decrease (response index = RI) were calculated in all studies. A higher accuracy was demonstrated for RI (mean sensitivity = 82%; pooled specificity = 85%) with a mean cut-off of 42%. The mean time point to perform PET scan during CRT resulted to be at 1.85 weeks. Some PET parameters resulted to be both predictive and not statistical predictive of response, maybe due to the small population and few studies bias.

CONCLUSION

PET showed high accuracy in early prediction response during preoperative CRT, increased with the use of RI as parameter. In the era of tailored treatment, the precocious assessment of non-responder patients allows modification of the subsequent strategy especially the timing and the type of surgical approach.

A systematic review of the predictive value of 18F-fluoro-2-deoxyglucose positron emission tomography on survival in locally advanced rectal cancer after neoadjuvant chemoradiation

AIM

Treatment of locally advanced rectal cancer (LARC) includes preoperative radiation therapy with or without chemotherapy followed by radical surgery, but the clinical outcome is uncertain. A systemic review was carried out to determine the predictive value of (18)F-fluoro-2-deoxyglucose positron emission tomography ((18)FDG-PET) for assessing disease-free (DFS) and overall survival (OS) in LARC.

METHOD

A literature search (PubMed/MEDLINE, EMBASE, Cochrane) up to January 2012 to identify full papers with sequential (18)FDG-PET and survival data, using indexing terms and free text words. The inclusion criteria were: a study of at least 10 patients, having sequential (18)FDG-PET imaging before and after adjuvant chemoradiation and a minimal follow-up of 24 months. Studies were selected by two of the authors. A meta-analysis was performed for DFS and OS using the hazard ratio (HR) as the primary outcome.

RESULTS

Five eligible studies were identified including 330 patients (mean age 63 years, 64% men), in which PET-CT or PET imaging was used. The American Joint Committee on Cancer stage distribution was as follows: Stage I, 2%; Stage II, 44%; Stage III, 52%; Stage IV, 1%. The pooled HRs for complete metabolic response versus partial or no response were 0.39 (95% CI 0.18-0.86; P = 0.02) for OS and 0.70 (95% CI 0.16-3.14; P = 0.64) for DFS. The lack of significance for DFS might be explained by different follow-up characteristics. There was also clinical heterogeneity among the different studies.

CONCLUSION

This systematic review indicates that complete metabolic response on sequential (18)FDG-PET data after preoperative chemoradiation of LARC is predictive of OS, but not of DFS.

Tumor regression grades: can they influence rectal cancer therapy decision tree?

Background. Evaluating impact of tumor regression grade in prognosis of patients with locally advanced rectal cancer (LARC). Materials and Methods. We identified from our colorectal cancer database 168 patients with LARC who received neoadjuvant therapy followed by complete mesorectum excision surgery between 2003 and 2011: 157 received 5-FU-based chemoradiation (CRT) and 11 short course RT. We excluded 29 patients, the remaining 139 were reassessed for disease recurrence and survival; the slides of surgical specimens were reviewed and classified according to Mandard tumor regression grades (TRG). We compared patients with good response (Mandard TRG1 or TRG2) versus patients with bad response (Mandard TRG3, TRG4, or TRG5). Outcomes evaluated were 5-year overall survival (OS), disease-free survival (DFS), local, distant and mixed recurrence. Results. Mean age was 64.2 years, and median followup was 56 months. No statistically significant survival difference was found when comparing patients with Mandard TRG1 versus Mandard TRG2 (p = .77). Mandard good responders (TRG1 + 2) have significantly better OS and DFS than Mandard bad responders (TRG3 + 4 + 5) (OS p = .013; DFS p = .007). Conclusions. Mandard good responders had a favorable prognosis. Tumor response (TRG) to neoadjuvant chemoradiation should be taken into account when defining the optimal adjuvant chemotherapy regimen for patients with LARC.

Optimizing the role of FDG PET-CT for potentially operable metastatic colorectal cancer

Recent treatment advances now allow a realistic chance of cure in selected patients with metastatic colorectal carcinoma (CRC). Accurate pre-treatment staging is crucial to ensure appropriate management by identification of patients with more advanced disease who will not benefit from surgery. (18)Fluorine 2-fluoro-2-deoxy-D-glucose positron emission tomography-computed tomography (PET-CT) has a firmly established role in staging, restaging, and recurrence detection of a range of tumors. This article will review the role of PET-CT in patients with CRC with a particular emphasis on optimizing the technique in patients with potentially operable metastatic disease.

Existem benefícios com a cirurgia retardada após radioterapia e quimioterapia neoadjuvante no câncer de reto localmente avançado?

RACIONAL: Tratamento neoadjuvante com radioterapia e quimioterapia é o esquema preferencial para câncer de reto localmente avançado, tendo por objetivo aumentar a ressecabilidade e diminuir a recidiva local. OBJETIVO: Avaliar os benefícios da operação tardia após radioterapia e quimioterapia neoadjuvante em câncer de reto localmente avançado quanto à resposta da regressão tumoral, sobrevida e efeitos adversos. MÉTODOS: Foram tratados consecutivamente 106 pacientes, portadores de adenocarcinoma do reto localmente avançado no período pré-operatório com radioterapia na dose de 50,4 Gy (28 frações) e quimioterapia com 5-fluoracil e leucovorin. A operação foi programada entre cinco e seis semanas. Pacientes que retornaram após seis semanas por motivos diversos foram agrupados em grupo de operação tardia. Variáveis como diminuição do estádio, remissão tumoral completa, tempo cirúrgico, transfusão sanguínea, recidiva local, metástase e sobrevida foram correlacionadas com o restante dos pacientes a fim de verificar os seus benefícios. RESULTADOS: Remissão completa do tumor foi encontrada em 15 pacientes (T0=15/106 - 14,2%). Resposta parcial em 38 (34,9%); entretanto em um paciente a resposta foi pT0N2. O seguimento médio foi 35,6 semanas e 32,2 semanas para grupo de operação em seis semanas e grupo de cirurgia tardia. Não houve diferença entre os dois grupos quanto à diminuição de estádio, remissão tumoral completa, tempo cirúrgico, transfusão sanguínea e complicações cirúrgicas precoces. Embora a operação tardia não apresentasse diferença significante quanto à recidiva local (p=0,1468), ela mostrou tendência em menor risco de metástase à distância (p=0,0520). CONCLUSÃO: Operação tardia após tratamento neoadjuvante não oferece benefícios evidentes em termos de remissão completa ou diminuição do estádio tumoral. Fatores moleculares preditivos devem ser investigados no futuro para melhor seleção de doentes que poderão beneficiar-se com o tratamento neoadjuvante.

Fifteen different 18F-FDG PET/CT qualitative and quantitative parameters investigated as pathological response predictors of locally advanced rectal cancer treated by neoadjuvant chemoradiation therapy

PURPOSE

The aim of this study was to correlate qualitative visual response and various PET quantification factors with the tumour regression grade (TRG) classification of pathological response to neoadjuvant chemoradiotherapy (CRT) proposed by Mandard.

METHODS

Included in this retrospective study were 69 consecutive patients with locally advanced rectal cancer (LARC). FDG PET/CT scans were performed at staging and after CRT (mean 6.7 weeks). Tumour SUVmax and its related arithmetic and percentage decrease (response index, RI) were calculated. Qualitative analysis was performed by visual response assessment (VRA), PERCIST 1.0 and response cut-off classification based on a new definition of residual disease. Metabolic tumour volume (MTV) was calculated using a 40 % SUVmax threshold, and the total lesion glycolysis (TLG) both before and after CRT and their arithmetic and percentage change were also calculated. We split the patients into responders (TRG 1 or 2) and nonresponders (TRG 3-5).

RESULTS

SUVmax MTV and TLG after CRT, RI, ΔMTV% and ΔTLG% parameters were significantly correlated with pathological treatment response (p < 0.01) with a ROC curve cut-off values of 5.1, 2.1 cm(3), 23.4 cm(3), 61.8 %, 81.4 % and 94.2 %, respectively. SUVmax after CRT had the highest ROC AUC (0.846), with a sensitivity of 86 % and a specificity of 80 %. VRA and response cut-off classification were also significantly predictive of TRG response (VRA with the best accuracy: sensitivity 86 % and specificity 55 %). In contrast, assessment using PERCIST was not significantly correlated with TRG.

CONCLUSION

FDG PET/CT can accurately stratify patients with LARC preoperatively, independently of the method chosen to interpret the images. Among many PET parameters, some of which are not immediately obtainable, the most commonly used in clinical practice (SUVmax after CRT and VRA) showed the best accuracy in predicting TRG.

Is the standardized uptake value of FDG-PET/CT predictive of pathological complete response in locally advanced rectal cancer treated with capecitabine-based neoadjuvant chemoradiation?

OBJECTIVES

Our aim was to assess FDG-PET/CT as a surrogate biomarker of the pathological complete response in locally advanced rectal cancer treated with neoadjuvant chemoradiation.

METHODS

T3-4 and/or N+ rectal cancer patients were treated prospectively with capecitabine-based chemoradiation and total mesorectal excision 7-8 weeks later. FDG-PET/CT uptake was obtained at baseline, after 2 weeks, and 6 weeks following treatment completion, calculating the maximum standardized uptake value (SUV) and percentage difference to identify the early and late metabolic 'response index'.

RESULTS

Thirty-one patients were treated from January 2009 to January 2012 at the Istituto Nazionale dei Tumori of Milan. One patient was excluded due to surgery refusal. The pathological complete response rate was 30%. Early FDG-PET/CT was performed in 24 consenting patients and failed to show predictive utility. On the contrary, significant differences in late SUV value and response index were observed between complete and noncomplete pathological responders (p = 0.0006 and 0.03). In multivariate analysis including most relevant SUV parameters, none of them was independently associated with a pathological complete response. With receiver operating characteristic curve analysis, a late SUV threshold <5.4 had 81% sensitivity and 100% specificity, with 90% overall accuracy.

CONCLUSIONS

We evidenced a possible predictive role of late FDG-PET/CT for the assessment of pathological response in locally advanced rectal cancer following neoadjuvant chemoradiation.

Organ-preserving therapy for rectal cancer

SUMMARY Total mesorectal excision has resulted in low local recurrence rates in rectal cancer patients; however, it is associated with a significant impairment in quality of life. The operation may be disfiguring and cause permanent effects on gastrointestinal, genitourinary and sexual function. Recently, researchers have identified subgroups of rectal cancer patients who may be able to forgo total mesorectal excision without compromising their oncological outcomes. Two groups of patients are candidates for organ preservation: those with early-stage disease that may be adequately addressed by a more limited resection, and those with locally advanced disease that has responded completely to neoadjuvant therapy. Additionally, radiation alone may be curative in both early and locally advanced disease. This article reviews the data regarding these approaches.

Early FDG PET response assessment of preoperative radiochemotherapy in locally advanced rectal cancer: correlation with long-term outcome

PURPOSE

The aim of the present study is to prospectively evaluate the prognostic value of previously defined [(18)F]2-fluoro-2-deoxy-D-glucose positron emission tomography (FDG PET) criteria of early metabolic response in patients with locally advanced rectal cancer (LARC) after long-term follow-up.

METHODS

Forty-two patients with poor prognosis LARC underwent three biweekly courses of chemotherapy with oxaliplatin, raltitrexed and 5-fluorouracil modulated by levofolinic acid during pelvic radiotherapy. FDG PET studies were performed before and 12 days after the beginning of the chemoradiotherapy (CRT) treatment. Total mesorectal excision (TME) was carried out 8 weeks after completion of CRT. A previously identified cutoff value of ≥52 % reduction of the baseline mean FDG standardized uptake value (SUV(mean)) was applied to differentiate metabolic responders from non-responders and correlated to tumour regression grade (TRG) and survival.

RESULTS

Twenty-two metabolic responders showed complete (TRG1) or subtotal tumour regression (TRG2) and demonstrated a statistically significantly higher 5-year relapse-free survival (RFS) compared with the 20 non-responders (86 vs 55 %, p = .014) who showed TRG3 and TRG4 pathologic responses. A multivariate analysis demonstrated that early ∆SUV(mean) was the only pre-surgical parameter correlated to the likelihood of recurrence (p = .05).

CONCLUSION

This study is the first prospective long-term evaluation demonstrating that FDG PET is not only an early predictor of pathologic response but is also a valuable prognostic tool. Our results indicate the potential of FDG PET for optimizing multidisciplinary management of patients with LARC.

Early prediction of histopathological response of rectal tumors after one week of preoperative radiochemotherapy using 18 F-FDG PET-CT imaging. A prospective clinical study

BACKGROUND

Preoperative radiochemotherapy (RCT) is standard in locally advanced rectal cancer (LARC). Initial data suggest that the tumor's metabolic response, i.e. reduction of its 18 F-FDG uptake compared with the baseline, observed after two weeks of RCT, may correlate with histopathological response. This prospective study evaluated the ability of a very early metabolic response, seen after only one week of RCT, to predict the histopathological response to treatment.

METHODS

Twenty patients with LARC who received standard RCT regimen followed by radical surgery participated in this study. Maximum standardized uptake value (SUV-MAX), measured by PET-CT imaging at baseline and on day 8 of RCT, and the changes in FDG uptake (ΔSUV-MAX), were compared with the histopathological response at surgery. Response was classified by tumor regression grade (TRG) and by achievement of pathological complete response (pCR).

RESULTS

Absolute SUV-MAX values at both time points did not correlate with histopathological response. However, patients with pCR had a larger drop in SUV-MAX after one week of RCT (median: -35.31% vs -18.42%, p = 0.046). In contrast, TRG did not correlate with ΔSUV-MAX. The changes in FGD-uptake predicted accurately the achievement of pCR: only patients with a decrease of more than 32% in SUV-MAX had pCR while none of those whose tumors did not show any decrease in SUV-MAX had pCR.

CONCLUSIONS

A decrease in ΔSUV-MAX after only one week of RCT for LARC may be able to predict the achievement of pCR in the post-RCT surgical specimen. Validation in a larger independent cohort is planned.

FDG-PET assessment of rectal cancer response to neoadjuvant chemoradiotherapy is not associated with long-term prognosis: a prospective evaluation

BACKGROUND

At present there is no defined role for routine FDG-PET in the preoperative evaluation of nonmetastatic rectal cancer.

OBJECTIVE

The primary objective of this study was to evaluate the ability of FDG-PET to predict long-term prognosis based on the response to neoadjuvant chemoradiotherapy in patients with locally advanced rectal cancer.

DESIGN

This was a prospective study.

SETTINGS

This study was performed at an academic, tertiary care, comprehensive cancer center.

PATIENTS

One hundred twenty-seven patients with locally advanced rectal cancer were enrolled between September 1999 and December 2005.

INTERVENTIONS

All patients underwent FDG-PET scans before and after neoadjuvant chemoradiotherapy.

MAIN OUTCOME MEASURES

FDG-PET parameters were evaluated by at least 2 study board-certified nuclear medicine physicians, and included mean standard uptake value, maximum standard uptake value, total lesion glycolysis, and visual response score. The main outcome measures were time to recurrence and disease-specific survival.

RESULTS

Of 127 patients, 82 (65%) were men, the median age was 60 years (range, 27-82), 110 patients had stage II/III disease, and 17 patients had stage IV disease. Median follow-up among survivors was 77 months (range, 1-115 months). Nine patients had unresectable metastatic disease and were excluded from the time-to-recurrence analysis. At 5 years, 74% (95% CI = 66%-81%) of patients had not had recurrences (locally and/or distantly). The 5-year disease-specific survival was 89% (95% CI = 81%-93%). On univariate analysis, visual response score and time to recurrence came closest to having an association (HR = 0.83, 95% CI = 0.68-1.01, p = 0.06). On multivariate analysis, the visual response score was not significant (p = 0.85). No FDG-PET parameter was associated with disease-specific survival.

CONCLUSIONS

Assessment of rectal cancer response to neoadjuvant chemoradiotherapy by FDG-PET provides no prognostic information. Therefore, serial FDG-PET before and after neoadjuvant chemoradiotherapy should not be performed for this purpose.

Predicting pathological response to neoadjuvant chemoradiotherapy in locally advanced rectal cancer using 18FDG-PET/CT

BACKGROUND

Pathologic complete response (pCR) after neoadjuvant chemoradiation (CRT) has been observed in 15-30% of patients with locally advanced rectal cancer (LARC). The objective of this study was to determine whether PET/CT can predict pCR and disease-free survival in patients receiving CRT with LARC.

METHODS

This is a retrospective review of patients with EUS-staged T3-T4, N+rectal tumors treated with CRT, who underwent pre/post-treatment PET/CT from 2002-2009. All patients were treated with CRT and surgical resection. Standardized uptake value (SUV) of each tumor was recorded. Logistic regression was used to analyze the association of pre-CRT SUV, post-CRT SUV, %SUV change, and time between CRT and surgery, compared with pCR. Kaplan-Meier estimation evaluated significant predictors of survival.

RESULTS

Seventy patients (age 62 years; 42M:28F) with preoperative stage T3 (n=61) and T4 (n=9) underwent pre- and post-CRT PET/CT followed by surgery. The pCR rate was 26%. Median pre-CRT SUV was 10.8, whereas the median post-CRT SUV was 4 (P=0.001). Patients with pCR had a lower median post-CRT SUV compared with those without (2.7 vs. 4.5, P=0.01). Median SUV decrease was 63% (7.5-95.5%) and predicted pCR (P=0.002). Patients with a pCR had a greater time interval between CRT and surgery (median, 58 vs. 50 days) than those without (P=0.02). Patients with post-CRT SUV<4 had a lower recurrence compared with those without (P=0.03). Patients with SUV decrease≥63% had improved overall survival at median follow-up of 40 months than those without (P=0.006).

CONCLUSIONS

PET/CT can predict response to CRT in patients with LARC. Posttreatment SUV, %SUV decrease, and greater time from CRT to surgery correlate with pCR. Post-CRT, SUV<4, and SUV decrease≥63% were predictive of recurrence-free and overall survival.

Avoiding radical surgery after pre-operative chemoradiotherapy: a possible therapeutic option in rectal cancer?

BACKGROUND

In this modern era of multi-modality treatment there is increasing interest in the possibility of avoiding radical surgery in complete responders after neo-adjuvant long-course chemoradiotherapy (LCPRT). In this article, we present a systematic review of such treatments and discuss their therapeutic applicability for the future.

METHODS

We searched the PubMed online libraries to identify studies that reported on the long-term surgical and pathological outcomes after local excision together with those that explored the possibility of clinical observation only in patients achieving a complete clinical response after LCPRT.

RESULTS

Several retrospective (n = 10), one single-arm prospective, and one small randomised series have reported on the use of local excision after LCPRT and demonstrated acceptably low levels of local recurrence with survival comparable to patients progressing to conventional surgery. One prospective series allocated patients to observation or radical surgery based on histological parameters after local excision (ypT0 and ypT1) and showed no differences in outcomes. Two retrospective series from the same group on a Brazilian cohort of patients reported excellent long-term outcomes after "wait and watch" in complete clinical responders. However, other reports have shown no direct correlation between clinical and pathological response.

CONCLUSION

Local excision may be an appropriate option for selected patients developing good clinical response after LCPRT. In our opinion, a policy of clinical observation in complete clinical responders after LCPRT may not be a safe strategy, unless we had robust predictive models for accurate identification of pathological complete response. In order to identify patients that may be potentially appropriate for such an approach we propose a clinical algorithm incorporating important clinical, radiological, and pathological parameters. The proposed model will require validation in a prospective study. Finally, we need randomised data for demonstrating the non-inferiority of clinical observation compared to conventional surgery before this can be considered as standard possible therapeutic option.

Potential role of FDG PET imaging in predicting metastatic potential and assessment of therapeutic response to neoadjuvant chemotherapy in Ewing sarcoma family of tumors

AIMS AND OBJECTIVES

The aim of this study was to retrospectively correlate FDG uptake in primary Ewing sarcoma family of tumors (ESFT) with tumor behavior, and to evaluate whether FDG PET can be used to predict response to neoadjuvant chemotherapy (NACT) in this patient group.

METHODS

Out of the total 54 patients of recently diagnosed ESFT who underwent pretreatment FDG PET imaging, group I included patients without metastasis at presentation (n = 34) and group II included those with metastasis at presentation (n = 20). Fourteen of these patients had undergone FDG PET after 4 cycles of induction chemotherapy and surgical resection of primary tumor. In this subgroup of 14 patients, maximum standardized uptake value (SUVmax) of primary tumor was estimated before and after 4 cycles of induction chemotherapy and was correlated with the histopathological response in terms of necrosis in the tumor specimen.

RESULTS

Mean SUVmax in the primary tumor in group I patients was 6.84 and in group II patients, it was 11.31. The difference between mean SUVmax of these 2 groups was significant by Wilcoxon test analysis, with P < 0.01. In group II patients, SUVmax in metastasis with maximum FDG uptake was consistently lower as compared with that of primary tumor. In subgroup of 14 patients, Pearson correlation analysis showed that percentage change in SUVmax of primary tumor correlated well with percentage necrosis on histopathological examination (P < 0.01).

CONCLUSION

FDG uptake in primary ESFT reflected its metastatic potential and hence the aggressive behavior. The significant correlation between change in metabolic activity of the primary tumor and histopathological response after neoadjuvant chemotherapy suggests that FDG PET may be an ideal noninvasive method to assess tumor behavior and response to therapy in ESFT.

Selection criteria for the radical treatment of locally advanced rectal cancer

There are over 14,000 newly diagnosed rectal cancers per year in the United Kingdom of which between 50 and 64 percent are locally advanced (T₃/T₄) at presentation. Pelvic exenterative surgery was first described by Brunschwig in 1948 for advanced cervical cancer, but early series reported high morbidity and mortality. This approach was later applied to advanced primary rectal carcinomas with contemporary series reporting 5-year survival rates between 32 and 66 percent and to recurrent rectal carcinoma with survival rates of 22–42%. The Swansea Pelvic Oncology Group was established in 1999 and is involved in the assessment and management of advanced pelvic malignancies referred both regionally and UK wide. This paper will set out the selection, assessment, preparation, surgery, and outcomes from pelvic exenterative surgery for locally advanced primary rectal carcinomas.

Positron emission tomography and colorectal cancer

Colorectal cancer (CRC) is a major cause of cancer-related morbidity and mortality. Molecular imaging using positron emission tomography (PET) is now an integral part of multidisciplinary cancer care. In this review, we discuss the role of PET in CRC including well established indications in the assessment of recurrent disease and emerging applications such as initial staging, monitoring therapy efficacy and using PET for radiotherapy planning. With rapid advancement in imaging technology, we also discuss the future potential of combining PET and magnetic resonance imaging and the use of novel radiotracers.

Repeated positron emission tomography-computed tomography and perfusion-computed tomography imaging in rectal cancer: fluorodeoxyglucose uptake corresponds with tumor perfusion

PURPOSE

The purpose of this study was to analyze both the intratumoral fluorodeoxyglucose (FDG) uptake and perfusion within rectal tumors before and after hypofractionated radiotherapy.

METHODS AND MATERIALS

Rectal cancer patients, referred for preoperative hypofractionated radiotherapy (RT), underwent FDG-positron emission tomography (PET)-computed tomography (CT) and perfusion-CT (pCT) imaging before the start of hypofractionated RT and at the day of the last RT fraction. The pCT-images were analyzed using the extended Kety model, quantifying tumor perfusion with the pharmacokinetic parameters K(trans), v(e), and v(p). The mean and maximum FDG uptake based on the standardized uptake value (SUV) and transfer constant (K(trans)) within the tumor were correlated. Also, the tumor was subdivided into eight subregions and for each subregion the mean and maximum SUVs and K(trans) values were assessed and correlated. Furthermore, the mean FDG uptake in voxels presenting with the lowest 25% of perfusion was compared with the FDG uptake in the voxels with the 25% highest perfusion.

RESULTS

The mean and maximum K(trans) values were positively correlated with the corresponding SUVs (ρ = 0.596, p = 0.001 and ρ = 0.779, p < 0.001). Also, positive correlations were found for K(trans) values and SUVs within the subregions (mean, ρ = 0.413, p < 0.001; and max, ρ = 0.540, p < 0.001). The mean FDG uptake in the 25% highest-perfused tumor regions was significantly higher compared with the 25% lowest-perfused regions (10.6% ± 5.1%, p = 0.017). During hypofractionated radiotherapy, stable mean (p = 0.379) and maximum (p = 0.280) FDG uptake levels were found, whereas the mean (p = 0.040) and maximum (p = 0.003) K(trans) values were found to significantly increase.

CONCLUSION

Highly perfused rectal tumors presented with higher FDG-uptake levels compared with relatively low perfused tumors. Also, intratumor regions with a high FDG uptake demonstrated with higher levels of perfusion than regions with a relatively low FDG-uptake. Early after hypofractionated RT, stable FDG uptake levels were found, whereas tumor perfusion was found to significantly increase.

PET-based treatment response evaluation in rectal cancer: prediction and validation

PURPOSE

To develop a positron emission tomography (PET)-based response prediction model to differentiate pathological responders from nonresponders. The predictive strength of the model was validated in a second patient group, treated and imaged identical to the patients on which the predictive model was based.

METHODS AND MATERIALS

Fifty-one rectal cancer patients were prospectively included in this study. All patients underwent fluorodeoxyglucose (FDG) PET-computed tomography (CT) imaging both before the start of chemoradiotherapy (CRT) and after 2 weeks of treatment. Preoperative treatment with CRT was followed by a total mesorectal excision. From the resected specimen, the tumor regression grade (TRG) was scored according to the Mandard criteria. From one patient group (n = 30), the metabolic treatment response was correlated with the pathological treatment response, resulting in a receiver operating characteristic (ROC) curve based cutoff value for the reduction of maximum standardized uptake value (SUV(max)) within the tumor to differentiate pathological responders (TRG 1-2) from nonresponders (TRG 3-5). The applicability of the selected cutoff value for new patients was validated in a second patient group (n = 21).

RESULTS

When correlating the metabolic and pathological treatment response for the first patient group using ROC curve analysis (area under the curve = 0.98), a cutoff value of 48% SUV(max) reduction was selected to differentiate pathological responders from nonresponders (specificity of 100%, sensitivity of 64%). Applying this cutoff value to the second patient group resulted in a specificity and sensitivity of, respectively, 93% and 83%, with only one of the pathological nonresponders being false positively predicted as pathological responding.

CONCLUSIONS

For rectal cancer, an accurate PET-based prediction of the pathological treatment response is feasible already after 2 weeks of CRT. The presented predictive model could be used to select patients to be considered for less invasive surgical interventions or even a "wait and see" policy. Also, based on the predicted response, early modifications of the treatment protocol are possible, which might result in an improved clinical outcome.

Change in glucose metabolism measured by 18F-FDG PET/CT as a predictor of histopathologic response to neoadjuvant treatment in rectal cancer

PURPOSE

In order to analyze the changes of glucose metabolism by maximum standardized uptake value (SUVmax) of 18F-FDG PET/CT in patients with rectal cancer submitted to neoadjuvant radiochemotherapy (nRCT) and to correlate SUV changes with tumor regression grade (TRG).

METHODS AND MATERIAL

Three sequential 18F-FDG PET/CT studies were performed in 31 patients with rectal cancer at the following time point: before starting the treatment (PET/CT1), during the treatment (PET/CT2), and after completion of neoadjuvant treatment (PET/CT3). The SUVmax values of the rectal lesion in the PET/CT1 (SUV1), PET/CT2 (SUV2), and PET/CT3 (SUV3) were obtained; deltaSUV1 [(SUV1 - SUV2)/SUV1] and deltaSUV2 [(SUV1 - SUV3)/SUV1] were also calculated. Metabolic parameters were compared to TRG.

RESULTS

Significant differences in pathologic responder and non-responder patients were found only for SUV2 (6.4 ± 2.9 in responder and 10.7 ± 4.8 in non-responder patients, respectively; P = 0.006) and SUV3 (3.6 ± 1.4 in responder and 6.6 ± 2.1 in non-responder patients, respectively; P = 0.0009). The best predictor for TRG response was SUV3 (threshold of 4.4) with sensitivity, specificity, accuracy, negative predictive value, and positive predictive value of 77.3%, 88.9%, 80.7%, 61.5%, and 94.4%, respectively.

CONCLUSION

18F-FDG PET/CT is a reliable and accurate technique to assess the response to nRCT in rectal cancer. In our population, the absolute value of SUVmax after treatment was the best predictor of pathological response.

18Fluoro-deoxy-glucose positron emission tomography in assessing tumor response to preoperative chemoradiation therapy for locally advanced rectal cancer

BACKGROUND

This study aims to evaluate the efficacy of (18)F-FDG PET in assessing tumor response after preoperative chemoradiation therapy (CRT) for rectal cancer.

METHODS

Maximum standardized uptake value (SUV) was measured for 37 patients who underwent (18)F-FDG PET before and 4 weeks after completion of preoperative CRT. Pre-SUV, post-SUV, the difference between pre- and post-SUV (ΔSUV), and reduction rate (RR) were correlated with tumor response.

RESULTS

A lower mean post-SUV and a higher mean RR were shown in good tumor response (T-downstaging(+) and tumor regression grade 1, 2). Considering pathologic complete response (pCR), the mean post-SUV and the mean RR were significantly different between pCR (+) patients (N = 13) and pCR (-) patients (N = 24) (2.7 vs. 4.8, P < 0.001, 73.9% vs. 58.7%, P = 0.009). With a 3.35 cut-off value for the post-SUV by receiver operating characteristic analysis, 84.6% sensitivity, 79.2% specificity, and 81.2% overall accuracy were obtained for discriminating between pCR (+) and pCR (-) (area under the curve = 0.885, P < 0.001).

CONCLUSIONS

(18)F-FDG PET is potentially useful as a method for assessing tumor response after preoperative CRT for rectal cancer. Post-SUV and RR were significantly associated with pathological treatment response, especially in pCR.