A prospective study of 2-[18F] fluoro-2-deoxy-D-glucose/positron emission tomography scan, 99mTc-labeled arcitumomab (CEA-scan), and blind second-look laparotomy for detecting colon cancer recurrence in patients with increasing carcinoembryonic antigen levels

PET/CT in assessment of colorectal liver metastases: a comprehensive review with emphasis on 18F-FDG

Approximately 25% of those who are diagnosed with colorectal cancer will develop colorectal liver metastases (CRLM) as their illness advances. Despite major improvements in both diagnostic and treatment methods, the prognosis for patients with CRLM is still poor, with low survival rates. Accurate employment of imaging methods is critical in identifying the most effective treatment approach for CRLM. Different imaging modalities are used to evaluate CRLM, including positron emission tomography (PET)/computed tomography (CT). Among the PET radiotracers, fluoro-18-deoxyglucose (18F-FDG), a glucose analog, is commonly used as the primary radiotracer in assessment of CRLM. As the importance of 18F-FDG-PET/CT continues to grow in assessment of CRLM, developing a comprehensive understanding of this subject becomes imperative for healthcare professionals from diverse disciplines. The primary aim of this article is to offer a simplified and comprehensive explanation of PET/CT in the evaluation of CRLM, with a deliberate effort to minimize the use of technical nuclear medicine terminology. This approach intends to provide various healthcare professionals and researchers with a thorough understanding of the subject matter.

Selective Use of (18)F-Fluorodeoxyglucose-Positron Emission Tomography and Computed Tomography in the Management of Metastatic Disease from Colorectal Cancer: Results from a regional centre

OBJECTIVES

Computed tomography (CT) scans are routinely used for primary staging and disease surveillance in patients with colorectal cancer. However, these scans have limited sensitivity in some organs and can only detect lesions with morphological changes, whereas (18)F-fluorodeoxyglucose-positron emission tomography ((18)F-FDG-PET) scans are able to detect areas of metabolic change before morphological changes appear. The aim of this study was to evaluate the impact of (18)F-FDG-PET/CT scans over conventional imaging during preoperative work-ups or follow-ups in a selected group of patients.

METHODS

This retrospective cohort study, which took place between July 2009 and May 2011, assessed 1,043 patient records from the South East Scotland Cancer Network colorectal cancer database. A total of 102 patients who underwent (18)F-FDG-PET/CT scans in addition to conventional imaging were included in the study. These patients had potentially resectable metastases, equivocal findings on CT scans and elevated carcinoembryonic antigen levels with negative conventional imaging.

RESULTS

Of the 102 patients included in the study, 22 underwent a preoperative (18)F-FDG-PET/CT scan and 80 underwent a follow-up 18F-FDG-PET/CT scan. In the preoperative scan group, the (18)F-FDG-PET/CT scan had a major impact on 16 patients (72.75%) and no impact on six patients (27.25%). In the follow-up scan group, the (18)F-FDG-PET/CT scan had a major impact on 51 (63.75%), a minor impact on four (5%), no impact on 22 (27.5%) and a negative impact on three (3.75%) patients.

CONCLUSION

The results of this study demonstrated that (18)F-FDG-PET/CT scans have a considerable effect on disease management when undertaken among indicated colorectal cancer patients.

Current approaches and challenges for monitoring treatment response in colon and rectal cancer

Introduction: With the advent of multidisciplinary and multimodality approaches to the management of colorectal cancer patients, there is an increasing need to define how we monitor response to novel therapies in these patients. Several factors ranging from the type of therapy used to the intrinsic biology of the tumor play a role in tumor response. All of these can aid in determining the ideal course of treatment, and may fluctuate over time, pending down-staging or progression of disease. Therefore, monitoring how disease responds to therapy requires standardization in order to ultimately optimize patient outcomes. Unfortunately, how best to do this remains a topic of debate among oncologists, pathologists, and colorectal surgeons. There may not be one single best approach. The goal of the present article is to shed some light on current approaches and challenges to monitoring treatment response for colorectal cancer.

Methods: A literature search was conducted utilizing PubMed and the OVID library. Key-word combinations included colorectal cancer metastases, neoadjuvant therapy, rectal cancer, imaging modalities, CEA, down-staging, tumor response, and biomarkers. Directed searches of the embedded references from the primary articles were also performed in selected circumstances.

Results: Pathologic examination of the post-treatment surgical specimen is the gold standard for monitoring response to therapy. Endoscopy is useful for evaluating local recurrence, but not in assessing tumor response outside of the limited information gained by direct examination of intra-lumenal lesions. Imaging is used to monitor tumors throughout the body for response, with CT, PET, and MRI employed in different circumstances. Overall, each has been validated in the monitoring of patients with colorectal cancer and residual tumors.

Conclusion: Although there is no imaging or serum test to precisely correlate with a tumor's response to chemo- or radiation therapy, these modalities, when used in combination, can aid in allowing clinicians to adjust medical therapy, pursue operative intervention, or (in select cases) identify complete responders. Improvements are needed, however, as advances across multiple modalities could allow appropriate selection of patients for a close surveillance regimen in the absence of operative intervention.

F-18 FDG PET/CT in the assessment of patients with unexplained CEA rise after surgical curative resection for colorectal cancer

PURPOSE

We evaluated the role of quantitative assessment by maximum standardized uptake value (SUVmax) on F-18 fluorodeoxyglucose [F-18]FDG positron emission tomography/computed tomography (PET/CT) in stratifying colorectal cancer (CRC) patients with unexplained carcinoembryonic antigen (CEA) rise after surgical curative resection.

MATERIAL AND METHODS

Forty asymptomatic patients (mean age, 64 ± 12 years) with previous CRC and current serum CEA levels >5 ng/ml underwent [F-18] FDG PET/CT 13 ± 3 months after complete surgical resection. The SUVmax was registered on anastomosis and peri-anastomotic tissue lesions, if present. The patients were followed for 24 ± 9 months thereafter. Re-intervention, evidence of newly discovered distant metastases, and death were recognized as main events and constituted surrogate end points. The receiver-operator-curve (ROC) analysis was performed to estimate the optimal SUVmax cut-off to predict patients at high risk of main events. PET/CT results were then related to disease outcome (overall survival; OS).

RESULTS

The mean SUVmax at the anastomotic site was 6.2 ± 3 (range 2.6-15). At multivariate logistic regression analysis, the anastomotic SUVmax remained as the only significant contributor to the prediction of the events (p = 0.004; OR 1.97). The ROC analysis recognized that the optimal threshold of SUVmax to differentiate patients was 5.7. A worse OS was observed in patients presenting with a SUVmax greater than 5.7 as compared to those having lesser (median survival: 16 vs. 31 months; p = 0.002).

CONCLUSIONS

The quantitative assessment by SUVmax on [F-18]FDG PET/CT may be helpful in patients presenting with unexplained CEA rise after curative resection of CRC, by identifying those at risk of main events.

Use of FDG-PET or PET/CT to detect recurrent colorectal cancer in patients with elevated CEA: a systematic review and meta-analysis

AIM

The purpose of the present study was to conduct a systematic review and meta-analysis of the published literature to assess the diagnostic performance of FDG-PET or PET/CT in the detection of recurrent colorectal cancer (CRC) rising in patients with elevated CEA.

MATERIALS AND METHODS

The authors conducted a systematic MEDLINE search of published articles. Two reviewers independently assessed the methodological quality of each study. We estimated pooled sensitivity and specificity and positive and negative likelihood ratios, and summary receiver-operating characteristic curves in the detection of recurrent CRC in patients with elevated CEA.

RESULTS

Eleven studies with a total of 510 patients met the inclusion criteria. One hundred and six patients (106/510 = 20.8%) had true-negative FDG-PET (PET/CT) results in detection of recurrent CRC when rising CEA. The pooled estimates of sensitivity and specificity and positive and negative likelihood ratios of FDG-PET in the detection of tumor recurrence in CRC patients with elevated CEA were 90.3% (95% CI, 85.5-94.0%), 80.0% (95% CI, 67.0-89.6%), 2.88 (95% CI, 1.37-6.07), and 0.12 (95% CI, 0.07-0.20), respectively. The pooled estimates of sensitivity and specificity and positive and negative likelihood ratios of FDG-PET/CT in the detection of tumor recurrence in CRC patients with elevated CEA were 94.1% (95% CI, 89.4-97.1%), 77.2% (95% CI, 66.4-85.9%), 4.70 (95% CI, 0.82-12.13), and 0.06 (95% CI, 0.03-0.13), respectively.

CONCLUSIONS

Whole-body FDG-PET and PET/CT are valuable imaging tools for the assessment of patients with suspected CRC tumor recurrence based on the increase of CEA.

Selecting Potential Targetable Biomarkers for Imaging Purposes in Colorectal Cancer Using TArget Selection Criteria (TASC): A Novel Target Identification Tool

Peritoneal carcinomatosis (PC) of colorectal origin is associated with a poor prognosis. However, cytoreductive surgery combined with hyperthermic intraperitoneal chemotherapy is available for a selected group of PC patients, which significantly increases overall survival rates up to 30%. As a consequence, there is substantial room for improvement. Tumor targeting is expected to improve the treatment efficacy of colorectal cancer (CRC) further through 1) more sensitive preoperative tumor detection, thus reducing overtreatment; 2) better intraoperative detection and surgical elimination of residual disease using tumor-specific intraoperative imaging; and 3) tumor-specific targeted therapeutics. This review focuses, in particular, on the development of tumor-targeted imaging agents. A large number of biomarkers are known to be upregulated in CRC. However, to date, no validated criteria have been described for the selection of the most promising biomarkers for tumor targeting. Such a scoring system might improve the selection of the correct biomarker for imaging purposes. In this review, we present the TArget Selection Criteria (TASC) scoring system for selection of potential biomarkers for tumor-targeted imaging. By applying TASC to biomarkers for CRC, we identified seven biomarkers (carcinoembryonic antigen, CXC chemokine receptor 4, epidermal growth factor receptor, epithelial cell adhesion molecule, matrix metalloproteinases, mucin 1, and vascular endothelial growth factor A) that seem most suitable for tumor-targeted imaging applications in colorectal cancer. Further cross-validation studies in CRC and other tumor types are necessary to establish its definitive value.

Role of FDG-PET staging in selecting the optimum patient for hepatic resection of metastatic colorectal cancer

Staging by FDG-PET of patients who are candidates for surgical treatment of colorectal metastases is an essential part of management of this problem. FDG-PET is highly sensitive and specific for intrahepatic colorectal tumors and the most sensitive test for extrahepatic tumors. FDG-PET alters management in 25% of patients, reducing futile laparotomies and hepatectomies.

Imaging in targeted delivery of therapy to cancer

We review the current status of imaging as applied to targeted therapy with particular focus on antibody-based therapeutics. Antibodies have high tumor specificity and can be engineered to optimize delivery to, and retention within, the tumor. Whole antibodies can activate natural immune effector mechanisms and can be conjugated to beta- and alpha-emitting radionuclides, toxins, enzymes, and nanoparticles for enhanced therapeutic effect. Imaging is central to the development of these agents and is used for patient selection, performing dosimetry and assessment of response. gamma- and positron-emitting radionuclides may be used to image the distribution of antibody-targeted therapeutics While some radionuclides such as iodine-131 emit both beta and gamma radiation and are therefore suitable for both imaging and therapy, others are more suited to imaging or therapy alone. Hence for radionuclide therapy of neuroendocrine tumors, patients can be selected for therapy on the basis of gamma-emitting indium-111-octreotide imaging and treated with beta-emitting yttrium-90-octreotate. Positron-emitting radionuclides can give greater sensitivity that gamma-emitters but only a single radionuclide can be imaged at one time and the range of radionuclides is more limited. The multiple options for antibody-based therapeutic molecules, imaging technologies and therapeutic scenarios mean that very large amounts of diverse data are being acquired. This can be most effectively shared and progress accelerated by use of common data standards for imaging, biological, and clinical data.

Brain metastases in colorectal cancers

BACKGROUND

Although colorectal cancer is the most common cancer in Singapore, brain metastases associated with colorectal primaries are quite rare, with reported incidences ranging from less than 1% to 4%. This is a review of the incidence, presentation, and prognosis of brain secondaries from colorectal primaries in our institution.

METHODS

From a prospectively collected database, 4378 patients underwent surgery for colorectal cancers between 1995 and 2003. Patients who developed brain metastases were identified and their records reviewed retrospectively.

RESULTS

Twenty-seven patients who developed brain metastases were identified, for an incidence of 0.62%. Seventy-one percent of the patients had a tumor in the rectum or sigmoid; 92.6% of patients had metachronous brain secondaries. The median interval between surgery for the primary tumor and the discovery of a brain secondary was 27.5 months. The lung was the most common site of concurrent metastatic disease, with the discovery of a brain secondary a median of 9.7 months after diagnosis of the lung lesion. All patients were symptomatic. The majority of the patients received nonsurgical treatment for the brain lesion. Median survival after diagnosis of brain secondaries was 2.4 months.

CONCLUSIONS

The poor survival of the patients in our series could be due to late diagnosis. It may be recommended that a brain scan be performed to screen for a brain secondary when lung and/or liver metastases are discovered, especially in a patient with a left-sided cancer. This may lead to earlier diagnosis, amenability to surgical treatment, and improved survival and quality of life.

Diagnostic value of FDG-PET in recurrent colorectal carcinoma: a meta-analysis

Accurate detection of recurrent colorectal carcinoma remains a diagnostic challenge. The purposes of this study were to evaluate the diagnostic value of Positron emission tomography (PET) using fluor-18-deoxyglucose (FDG) in recurrent colorectal carcinoma with a meta-analysis. All the published studies in English relating the diagnostic value of FDG-PET in the detection of recurrent colorectal carcinoma were collected. Methodological quality of the included studies was evaluated. Pooled sensitivity, specificity and diagnostic odds ratio and SROC (summary receiver operating characteristic curves) were obtained by the statistical software. Twenty-seven studies were included in the meta-analysis. The pooled sensitivity and specificity for FDG-PET detecting distant metastasis or whole body involvement in recurrent colorectal carcinoma were 0.91 (95% CI 0.88-0.92) and 0.83 (95% CI 0.79-0.87), respectively. The pooled sensitivity and specificity for FDG-PET detecting hepatic metastasis were 0.97 (95% CI 0.95-0.98) and 0.98 (95% CI 0.97-0.99). The pooled sensitivity and specificity for pelvic metastasis or local regional recurrence were 0.94 (95% CI 0.91-0.97) and 0.94 (95% CI 0.92-0.96). FDG-PET is valuable for the assessment of recurrent colorectal carcinoma.

Perspectives of tumour markers in gastrointestinal malignancies - an overview

There is an increasing incidence of GI cancers as per the Cancer Registry Data. In such a situation, it is essential to evaluate the patient by standard investigational tools like clinical examination and endoscopy which help in establishing the diagnosis. Determination of tumour markers is useful not only in diagnosis and prognosis of cancer but also monitoring of cancer treatment. Tumour markers in GI oncology include oncofoetal proteins, hormones, enzymes and cancer antigens. Recent advances include application of tumour marker level determination combined with newer radiological and functional imaging such as FDG PET - CT.

Clinical case report and literature review: metachronous colorectal splenic metastases

A 52-year-old woman with a rising carcinoembryonic antigen CEA, no clinical or radiological findings, a negative colonoscopy, and a positron emission tomography (PET) scan that revealed an isolated hypermetabolic lesion in the spleen. The patient underwent splenectomy by laparoscopic surgery. The pathological study confirmed the presence of an isolated metastasis to the spleen. This case reveals the rare occurrence of isolated splenic metastases in the context of colorectal cancer and illustrates the role of PET when a patient shows a rising CEA with negative clinicoradiological studies.

Radionuclide-Based Cancer Imaging Targeting the Carcinoembryonic Antigen

Carcinoembryonic antigen (CEA), highly expressed in many cancer types, is an important target for cancer diagnosis and therapy. Radionuclide-based imaging techniques (gamma camera, single photon emission computed tomography [SPECT] and positron emission tomography [PET]) have been extensively explored for CEA-targeted cancer imaging both preclinically and clinically. Briefly, these studies can be divided into three major categories: antibody-based, antibody fragment-based and pretargeted imaging. Radiolabeled anti-CEA antibodies, reported the earliest among the three categories, typically gave suboptimal tumor contrast due to the prolonged circulation life time of intact antibodies. Subsequently, a number of engineered anti-CEA antibody fragments (e.g. Fab’, scFv, minibody, diabody and scFv-Fc) have been labeled with a variety of radioisotopes for CEA imaging, many of which have entered clinical investigation. CEA-Scan (a ^99mTc-labeled anti-CEA Fab’ fragment) has already been approved by the United States Food and Drug Administration for cancer imaging. Meanwhile, pretargeting strategies have also been developed for CEA imaging which can give much better tumor contrast than the other two methods, if the system is designed properly. In this review article, we will summarize the current state-of-the-art of radionuclide-based cancer imaging targeting CEA. Generally, isotopes with short half-lives (e.g. ¹⁸F and ^99mTc) are more suitable for labeling small engineered antibody fragments while the isotopes with longer half-lives (e.g. ¹²³I and ¹¹¹In) are needed for antibody labeling to match its relatively long circulation half-life. With further improvement in tumor targeting efficacy and radiolabeling strategies, novel CEA-targeted agents may play an important role in cancer patient management, paving the way to “personalized medicine”.

Management of recurrent colorectal cancer with positron emission tomography

The use of positron emission tomography, on its own and in combination with computed tomography, has been integrated into the management algorithm of patients with suspected recurrence of colorectal cancer. This article looks at the biological basis of positron emission tomography, its clinical advantages and disadvantages.

Development of radioimmunotherapeutic and diagnostic antibodies: an inside-out view

Only a handful of radiolabeled antibodies (Abs) have gained US Food and Drug Administration (FDA) approval for use in clinical oncology, including four immunodiagnostic agents and two targeted radioimmunotherapeutic agents. Despite the advent of nonimmunogenic Abs and the availability of a diverse library of radionuclides, progress beyond early Phase II radioimmunotherapy (RIT) studies in solid tumors has been marginal. Furthermore, [18F]fluorodeoxyglucose continues to dominate the molecular imaging domain, underscored by a decade-long absence of any newly approved Ab-based imaging agent (none since 1996). Why has the development of clinically successful Abs for RIT been limited to lymphoma? What obstacles must be overcome to allow the FDA approval of immuno-positron emission tomography (immuno-PET) imaging agents? How can we address the unique challenges that have thus far prevented the introduction of Ab-based imaging agents and therapeutics for solid tumors? Many poor decisions have been made regarding radiolabeled Abs, but useful insight can be gained from these mistakes. The following review addresses the physical, chemical, biological, clinical, regulatory and financial limitations that impede the progress of this increasingly important class of drugs.

Detection and management of extrahepatic colorectal cancer in patients with resectable liver metastases

The presence of extrahepatic disease has a great effect on the management of patients with metastatic colorectal cancer in the liver. FDG-PET scanning is currently the most sensitive way of detecting extrahepatic metastases in such patients. This is supported by 10 studies, which show that FDG-PET scan will discover extrahepatic disease in about one in six patients who have completed standard imaging. Staging laparoscopy is another means of detecting extrahepatic disease. Its role remains undefined especially in patients who have had FDG-PET scans. It should probably be restricted to patients with high clinical risk scores. In terms of treatment, patients with recurrence at the primary colorectal site as well as resectable liver metastases appear to benefit from resection of both sites provided that R0 resections can be obtained. Resection of involved hepatic pedicle lymph nodes in patients with resectable liver metastases is associated with poor outcome. The situation regarding patients with peritoneal and liver metastases bears a strong resemblance to that of primary site recurrence and liver metastases. Very acceptable survival can be expected if the peritoneal disease can be eradicated. Information regarding treatment of lung and liver metastases is the most complete of any of these areas. Good results may be expected if all the disease can be cleared. Caution is required in interpreting claims of good survival when study numbers are small and confidence intervals of data are not provided.

Biodistribution and planar gamma camera imaging of 123I- and 131I-labeled F(ab′)2 and Fab fragments of monoclonal antibody 14C5 in nude mice bearing an A549 lung tumor

Detection of antigen 14C5, involved in substrate adhesion and highly expressed on the membrane of many carcinomas, including lung cancer, provides important diagnostic information that can influence patient management. The aim of this study was to evaluate the biodistribution and planar gamma camera imaging characteristics of radioiodinated F(ab')(2) and Fab fragments of monoclonal antibody (mAb) 14C5 in tumor-bearing mice.

METHODS

F(ab')(2) and Fab 14C5 fragments were radioiodinated using the Iodo-Gen method. In vitro stability, binding specificity and affinity of (125)I-labeled 14C5 fragments were studied in A549 lung carcinoma cells. Biodistribution, blood clearance and tumor-targeting characteristics of (131)I-labeled 14C5 fragments and intact mAb 14C5 were studied in Swiss nu/nu mice bearing A549 lung carcinoma tumors. Planar gamma imaging illustrated the potential use of these (123)I-labeled 14C5 fragments for radioimmunodetection (RID).

RESULTS

Saturation binding experiments showed highest affinity for (125)I-labeled F(ab')(2) fragments (K(d)=0.37+/-0.10 nmol/L) and lowest affinity for (125)I-labeled Fab fragments (K(d)=2.25+/-0.44 nmol/L). Blood clearance studies showed that the alpha half-life (t(1/2)alpha) value for Fab, F(ab')(2) and mAb 14C5 was 14.9, 21 and 118 min, respectively. The beta half-life t(1/2)beta value for Fab, F(ab')(2) and mAb 14C5 was 439, 627 and 4067 min, respectively. (131)I-Fab fragments showed highest tumor uptake 3 h after injection (2.4+/-0.8 %ID/g), (131)I-labeled F(ab')(2) showed highest tumor uptake 6 h after injection (4.7+/-0.7 %ID/g) and for (131)I-labeled mAb highest tumor uptake was observed at 24 h (10.7+/-2.3 %ID/g). In planar gamma imaging, both labeled fragments gave better tumor-to-background contrast than (123)I-mAb 14C5.

CONCLUSION

Fab and F(ab')(2) fragments derived from intact mAb 14C5 have significant potential for diagnostic and therapeutic applications and may provide new tools in mAb-based radiopharmaceuticals for targeting non-small cell lung cancer.

Tumour assessment in advanced melanoma: value of FDG-PET/CT in patients with elevated serum S-100B

PURPOSE

To evaluate the usefulness of PET/CT in melanoma patients with an elevated serum S-100B tumour marker level.

METHODS

Out of 165 consecutive high-risk melanoma patients referred for PET/CT imaging, 47 had elevated (>0.2 microg/l) S-100B serum levels and a contemporaneous 18F-FDG PET/CT scan. PET/CT scans were evaluated for the presence of metastases. To produce a composite reference standard, we used cytological, histological, MRI and PET/CT follow-up findings as well as clinical and S-100B follow-up.

RESULTS

Among the 47 patients with increased S-100B levels, PET/CT correctly identified metastases in 38 (30 distant metastases and eight lymph node metastases). In one patient with cervical lymph node metastases, PET/CT was negative. Eight patients had no metastases and PET/CT correctly excluded metastases in all of them. Overall sensitivity for metastases was 97% (38/39), specificity 100% (8/8) and accuracy 98% (46/47). S-100B was significantly higher in patients with distant metastases (mean 1.93 microg/l, range 0.3-14.3 microg/l) than in patients with lymph node metastases (mean 0.49 microg/l, range 0.3-1.6 microg/l, p=0.003) or patients without metastases (mean 0.625 microg/l, range 0.3-2.6 microg/l, p=0.007). However, 6 of 14 patients with a tumour marker level of 0.3 microg/l had no metastases.

CONCLUSION

In melanoma patients with elevated S-100B tumour marker levels, FDG-PET/CT accurately identifies lymph node or distant metastases and reliably excludes metastases. Because of the significant number of false positive S-100B tumour marker determinations (17%), we recommend repetition of tumour marker measurements if elevated S-100B levels occur before extensive imaging is used.

Recent evidences of the use of 18F-fluorodeoxyglucose positron emission tomography in the management of colorectal cancer

Positron emission tomography is considered a potentially useful diagnostic tool in the management of a variety of malignancies. It has been used for staging, evaluation of recurrent and metastatic disease, evaluation of tumoral response to neoadjuvant therapy, and providing prognostic information. However, some data are available about its definitive role in the colorectal cancer population. In this review, the most recent evidences and future perspectives are presented for the use of the 18F-fluorodeoxyglucose positron emission tomography in the management of patients with colorectal cancer.

The role of positron emission tomography in the management of recurrent colorectal cancer: a review

PURPOSE

Surgery remains the only option for potential cure in patients with recurrent colorectal cancer. Accurate staging modalities aid in the avoidance of futile surgery, which may result in considerable morbidity in patients with incurable disease. Current imaging techniques used in disease staging often are not sensitive enough to identify low-volume metastatic disease. This study reviews the role of positron emission tomography in the assessment of patients with suspected recurrent colorectal cancer.

METHODS

A literature search using the PubMed, MEDLINE, and Embase database was performed, locating English language articles on positron emission tomography, positron emission tomography, recurrent colon, and/or rectal cancer. The references of these papers were searched manually for further references.

RESULTS

Positron emission tomography is more sensitive and more specific than conventional diagnostic imaging for metastatic disease and local recurrence respectively. Studies confirm the superior ability of positron emission tomography scans compared with conventional diagnostic imaging in differentiating between scar tissue and invasive tumor. Positron emission tomography scanning is more sensitive and specific for the assessment of liver metastases (and probably in patients with lung metastasis) than conventional diagnostic imaging. Positron emission tomography is superior to conventional diagnostic imaging in the investigation of raised carcinoembryonic antigen in the postoperative patient and alters management in approximately 37 percent of patients with recurrent colorectal cancer. The limitations and cost effectiveness of positron emission tomography are discussed.

CONCLUSIONS

Positron emission tomography scanning is emerging as the imaging modality of choice for patients being considered for surgery for locally recurrent colorectal cancer. Positron emission tomography has the greatest impact by detecting unresectable disease and thereby averting inappropriate surgery. Despite the high set-up costs, its use seems to be cost effective.

FDG-PET in colorectal cancer

[18F]Fluorodeoxyglucose (FDG) positron emission tomography (PET) is a useful imaging tool in the evolving management of patients with colorectal carcinoma. This technique is able to measure and visualize metabolic changes in cancer cells. This feature results in the ability to distinguish viable tumor from scar tissue, in the detection of tumor foci at an earlier stage than possible by conventional anatomic imaging and in the measurement of alterations in tumor metabolism, indicative of tumor response to therapy. Nowadays, FDG-PET plays a pivotal role in staging patients before surgical resection of recurrence and metastases, in the localization of recurrence in patients with an unexplained rise in serum carcinoembryonic antigen and in assessment of residual masses after treatment. In the presurgical evaluation, FDG-PET may be best used in conjunction with anatomic imaging in order to combine the benefits of both anatomical (CT) and functional (PET) information, which leads to significant improvements in preoperative liver staging and preoperative judgment on the feasibility of resection. Integration of FDG-PET into the management algorithm of these categories of patients alters and improves therapeutic management, reduces morbidity due to futile surgery, leads to substantial cost savings and probably also to a better patient outcome. FDG-PET also appears to have great potential in monitoring the success of local ablative therapies soon after intervention and in the prediction and evaluation of response to radiotherapy, systemic therapy, and combinations thereof. This review aims to outline the current and future role of FDG-PET in the field of colorectal cancer.

The postoperative surveillance of patients with colon cancer and rectal cancer

BACKGROUND

Colon cancer is relatively common; however, the results of treatment have marginally improved over the last half century. Though about 85% of patients have colorectal tumors resected with curative intent, a significant number of these patients will eventually die from cancer. As a result, many clinicians have advocated intensive follow-up in such patients as an attempt to increase survival.

DATA SOURCES

A review of the literature focusing on studies that have specifically addressed postoperative surveillance programs in patients with colorectal cancer was conducted. Only studies with level A evidence were included. Further references were obtained through cross-referencing the bibliography cited in each work.

CONCLUSION

One of the six prospective randomized studies demonstrated a statistically significant survival benefit. Undoubtedly, survival benefits can be shown with a well-designed evidence-based follow-up strategy. However, well-designed large prospective multi-institutional randomized studies are needed to establish a consensus for follow-up.

Asymptomatic familial colon cancer with FDG-PET scanning for recurrent disease

A 57-yr-old female was referred for screening colonoscopy because of a positive family history of colon cancer. A lobulated tumor mass was detected in the sigmoid colon. The resected specimen showed an invasive adenocarcinoma without lymph node involvement. Later colonoscopic evaluations and CT imaging failed to reveal definite evidence of recurrent disease but a late rising carcinoembryonic antigen level led to FDG-PET scanning and the detection of suspect lymph nodes in the retroperitoneum. Further histopathological and immunohistochemical evaluation of resected lymph nodes confirmed metastatic carcinoma from the primary colon carcinoma with extra-nodal spread. This case underscores the ongoing need for additional evidence-based studies on evolving imaging modalities used in the diagnosis and management of colonic cancer.

Gastrointestinal malignancies evaluated with (18)F-fluoro-2-deoxyglucose positron emission tomography

(18)F-fluoro-2-deoxyglucose positron emission tomography has demonstrated high accuracy in the staging and evaluation of colorectal and esophageal carcinomas. FDG PET is demonstrating increasing utility in a number of other gastrointestinal tumours and clinical scenarios. The established clinical indications for its use, the diagnostic accuracy, and limitations will be reviewed. Data on the emerging indications and limitations for pancreatic, hepatocellular, and gastric carcinomas, as well as gastrointestinal stromal tumours, cholangiocarcinoma, and carcinoma of unknown primary will also be briefly discussed. The use of combined PET-CT is demonstrating further improvements in diagnostic accuracy.

Abdominal positron-emission tomography lesions with increased standardized uptake values correlate with intraoperative findings

BACKGROUND

The reporting of standardized uptake value (SUV) on fluoro-2-deoxy-D-glucose positron-emission tomography (FDG-PET) in colorectal cancer is becoming common practice, but its clinical utility remains to be determined. This study was designed to compare FDG-PET uptake as measured by SUV with operative findings.

METHODS

A colorectal cancer database was queried to identify patients who underwent FDG-PET scans with reported SUVs followed by exploratory laparotomy within 3 months and compare these results to determine FDG-PET sensitivity.

RESULTS

Of 46 patients, 16 (34.8%) were found to be have increased extent of disease intraoperatively than seen on FDG-PET scan. This patient population had a statistically significant decreased mean maximal SUV than the patients whose FDG-PET scan equaled intraoperative findings (P < .025).

CONCLUSIONS

This initial study indicates patients with potentially resectable disease by PET scan but decreased FDG uptake should undergo laparoscopic evaluation before performing laparotomy.

Effects of Onyx-015 among metastatic colorectal cancer patients that have failed prior treatment with 5-FU/leucovorin

Despite recent improvements in the treatment of metastatic colorectal cancer, few patients are cured and the response rates to second-line treatments are poor. Onyx-015, an oncolytic virus, was administered to patients with metastatic colorectal cancer by hepatic artery infusion. No dose-limiting toxicities were observed in the phase I/II studies. Onyx-015 can kill tumor cells by mechanisms that are distinct from chemotherapeutic agents and may therefore have activity among patients who have failed first-line chemotherapy. The 24 patients included in this analysis had failed first-line therapy with 5-FU/leucovorin, 79% of the patients failed two or more regimens and 58% had failed treatment with Irinotecan. Despite the extensive prior therapy, the median survival of these patients was 10.7 months, 46% were alive at 1 year and two patients (8%) had partial responses. In all, 11 patients (46%) had stable disease at the completion of the four planned viral treatments (3 months). The median survival of this group of patients was 19 months, suggesting that stable disease may be an important predictor of benefit with oncolytic viruses. Eight of the 11 patients with stable disease at 3 months demonstrated a unique radiographic pattern of transient enlargement of tumor masses (10-48%) after the initial infusions of Onyx-015, followed by radiographic evidence of extensive tumor necrosis and regression. The initial enlargement and subsequent tumor necrosis resulted in a prolonged time to achieve objective tumor regression. In addition, the transient enlargement of the tumor masses may have resulted in premature removal of responding patients. Treatment of eight patients was stopped prior to completion of the planned four treatments due to presumed progression as defined by standard radiographic criteria (>25% increase in tumor size). Functional imaging, such as positron emission tomography (PET) scans, may help distinguish clinical responses from progressive disease following treatment with oncolytic viruses. Onyx-015 may benefit patients with refractory colorectal cancer and additional studies that include PET scans to assess clinical response are warranted.

PET imaging in assessing gastrointestinal tumors

The clinical usefulness of FDG-PET imaging is now firmly established in various situations, such as the preoperative staging of esophageal cancer and recurrent colorectal carcinoma and the detection and staging of recurrent colorectal cancer when there is a clinical or biologic suspicion with inconclusive conventional findings. Encouraging results were obtained in the evaluation of the therapeutic response of various gastrointestinal malignancies, either during the treatment or after its completion. There is no firm consensus regarding its role in pancreatic cancer, either proved or suspected, but it may be valuable in selected clinical situations. Its role seems fairly limited in patients with hepatocellular carcinoma, although PET findings may have prognostic implications. Evaluation of cholangiocarcinoma is an emerging indication, albeit with limited data to date. Finally, PET/CT is very likely to enhance the role of FDG imaging further in the work-up of patients with gastrointestinal tumors.

Potential impact of [18F]3'-deoxy-3'-fluorothymidine versus [18F]fluoro-2-deoxy-D-glucose in positron emission tomography for colorectal cancer

Fluorine-18 labelled fluoro-2-deoxy- d-glucose ((18)FDG) positron emission tomography (PET) imaging demonstrates the increased glucose consumption of malignant cells, but problems with specificity have led to the development of new PET tracers. [(18)F]3'-deoxy-3'-fluorothymidine ((18)FLT) is a new tracer which images cellular proliferation by entering the salvage pathway of DNA synthesis. In this study we compared the cellular uptake of (18)FLT and (18)FDG in patients with colorectal cancer (CRC). Seventeen patients with 50 primary or metastatic CRC lesions were prospectively recruited. Lesions were initially identified using computed tomography. Patients underwent both (18)FDG and (18)FLT scanning. Semi-quantitative analysis of tracer uptake was carried out using standardised uptake values. All the primary tumours ( n=6) were visualised by both tracers, with (18)FDG showing on average twice the uptake of (18)FLT. Similar uptake of both tracers was seen in lung and peritoneal lesions, with (18)FLT imaging five of the six lung lesions and all of the peritoneal lesions. Of the 32 colorectal liver metastases, 11 (34%) were seen as avid for (18)FLT, compared with 31 (97%) for (18)FDG. No correlation was seen between the uptake of the two tracers ( R(2)=0.03). (18)FLT shows a high sensitivity in the detection of extrahepatic disease but poor sensitivity for the imaging of colorectal liver metastases, making it unlikely to have a role as a diagnostic tracer in CRC. We have demonstrated that (18)FDG and (18)FLT image two distinct processes. The prognostic implications of the uptake of (18)FLT need to be assessed in terms of response to chemoradiotherapy and survival.

The preoperative assessment and postoperative surveillance of patients with colon and rectal cancer

Many advances have been made in the field of colorectal cancer follow-up since the pioneering efforts of Wangensteen and others with second-look operations in the 1950s. The understanding of the biology and natural history of colorectal malignancy has been advanced. Diagnostic methods for detection of recurrent disease have also advanced tremendously with CEA monitoring, immunoscintigraphy. CT, MRI, and PET imaging. As has been discussed in this article, however, no strategy of postoperative follow-up has been shown unequivocally to produce improved survival benefit or cure rate. It is quite possible that benefit will be shown, but well-controlled trials will be required. Cost considerations will likely prove important, because the rate of detection of curable disease will likely.be low. Quality of life issues will also be important in such trials. Better treatment and outcome ol recurrent disease would provide a strong rationale for vigorous postoperative surveillance. New recommendations are currently evolving [54]. Early diagnosis seems likely to enhance the curability of both local and distant relapses and second primary tumors. Furthermore, there may be a survival and quality of life advantage that results from the early institution of chemotherapy, even for those tumors found to be inoperable [55]. In devising a plan for follow-up in patients, it is important to recognize the anatomic and temporal patterns of recurrence as well as their relationships to the initial tumor staging. Although there is little proof that the identification of recurrent disease in follow-up programs increases the likelihood of resectability, cure, or prolonged survival, many physicians have witnessed successful treatment of recurrent colorectal cancer. These anecdotal experiences, the unproven belief that follow-up is beneficial, and traditions imparted during training are among the likely motivating factors for most physicians caring for colorectal cancer patients.

Surgical treatment of rectal cancer

Rectal cancer should no longer be thought of as only a surgically treated disease. Centers that treat large numbers of rectal cancer patients should provide state of the art radiotherapy and chemotherapy as well as offer anatomic tumor-specific operations for advanced-stage cancers and local treatment options for favorable, early lesions.