- © 1999 by American Society of Clinical Oncology
Additional Value of Whole-Body Positron Emission Tomography With Fluorine-18-2-Fluoro-2-deoxy-d-glucose in Recurrent Colorectal Cancer
- Patrick Flamen,
- Sigrid Stroobants,
- Eric Van Cutsem,
- Patrick Dupont,
- Guy Bormans,
- Nancy De Vadder,
- Freddy Penninckx,
- Lieven Van Hoe and
- Luc Mortelmans
- From the Departments of Nuclear Medicine, Internal Medicine, Abdominal Surgery, and Radiology, University Hospital Gasthuisberg and Catholic University of Leuven, Leuven, Belgium.
- Address reprint requests to Patrick Flamen, MD, Department of Nuclear Medicine, University Hospital Gasthuisberg, Catholic University of Leuven, Herestraat 49, B-3000 Leuven, Belgium; email patrick.flamen_uz.kuleuven.ac.be
Abstract
PURPOSE: To assess the additional value of the whole-body [18F]-2-fluoro-2-deoxy-d-glucose positron emission tomography (FDG-PET) scan as a staging modality complementing conventional diagnostic methods (CDM) in patients suspected of having recurrent colorectal adenocarcinoma.
PATIENTS AND METHODS: In 103 patients, the discordances between FDG-PET and CDM results were identified and related to the final diagnosis obtained by histopathology or clinical follow-up (> 1 year). All FDG-PET studies were reviewed with full knowledge of the CDM findings.
RESULTS: In a region-based analysis, discordances between CDM and FDG-PET findings were found in 40 of 412 regions (10%). In these, FDG-PET had additional diagnostic value in 14 of 16 locoregional, six of seven hepatic, seven of eight abdominal, and eight of nine extra-abdominal regions. In a patient-based analysis, CDM categorized a subgroup of 60 patients as having resectable recurrent disease limited to the liver (n = 37) or locoregional region (n = 23). In 13 of these patients, there were discordant FDG-PET findings, detecting additional tumor sites in nine patients and excluding disease in three patients and yielding an additional diagnostic value in 20% of the patients. A second subgroup consisted of 13 patients with inconclusive CDM findings (n = 5) or with elevated plasma carcinoembryonic antigen levels and an otherwise negative conventional work-up (n = 8). In these patients, FDG-PET results were correct in eight of nine discordances, yielding a positive additional diagnostic value in 62% of the patients.
CONCLUSION: Whole-body FDG-PET can have a clear impact on the therapeutic management in the follow-up of patients with colorectal cancer.
IN PATIENTS WITH colorectal cancer, the recurrence rate after apparently curative resection of the primary tumor is 30% to 40%, and recurrent disease develops predominantly within 3 years after surgery.1 Approximately 25% of first colorectal cancer recurrences are isolated locoregional failures, and an additional 15% to 20% are metastatic deposits that are potentially resectable for cure.2 In those patients, for resection of liver metastases or pelvic recurrence to be curative, it is imperative that there be no unrecognized foci of tumoral disease outside the operation field. Presently, using standard preoperative diagnostic procedures, surgical treatment of recurrences leads to cure in 25% to 40% of the patients.3,4 Although the value of the conventional diagnostic methods (CDM) has improved in this setting, there still is a need for a highly accurate and noninvasive imaging modality to detect inoperable disease and select patients for curative surgery.
Recently, whole-body positron emission tomography (PET) has been advocated as a promising tool for staging recurrent colorectal adenocarcinoma.5-8 With the use of a labeled glucose analog, [18F]2-fluoro-2-deoxy-d-glucose (FDG), this technique detects malignancy by depicting increased glucose uptake and metabolism in cancer cells. The agent is transported into cells by means of epithelial glucose transporter proteins. Because FDG lacks a hydroxyl group in the two-position, its first metabolite, FDG-6-phosphate, is not a substrate for glucosephosphate isomerase and cannot be converted to the fructose analog. Owing to the negative charge on FDG-6-phosphate, it has a low membrane permeability and will accumulate intracellularly.9 Recent advances in technology allow the screening of the whole body in one examination session.10 The major impediment to the widespread application of this unique metabolic imaging tool is its limited availability owing to high cost and complexity. Therefore, definition of patient subsets most likely to benefit from this technique in a realistic environment of competing diagnostic modalities is mandatory. The purpose of this retrospective study was to evaluate the additional value of the whole-body FDG-PET scan as a staging modality complementary to CDM in patients with known or suspected recurrence of colorectal carcinoma.
PATIENTS AND METHODS
Patient Population
From June 1991 to June 1996, the nuclear medicine department at the University Hospital of Leuven performed a whole-body FDG-PET scan in 172 consecutive patients with a clinical suspicion of recurrent colorectal cancer or for preoperative staging in the case of previously proven recurrence. Only patients with a clinical and radiologic follow-up by the clinician at the university hospital were considered (n = 124). Patients who had undergone previous chemotherapeutic treatment for advanced disease (n = 8) and those with known inflammatory bowel disease (n = 6) were excluded. Patients with a time interval of more than 2 months between the abdominal computed tomographic (CT) scan and the PET scan were also excluded (n = 7). The selected group consisted of 103 patients (62 men and 41 women), with a mean age of 61 years (range, 35 to 81 years). All patients had undergone surgical resection of a primary adenocarcinoma located in the colon (n = 24) or in the rectum (n = 79). The mean time interval between primary surgery of the colorectal cancer and the FDG-PET scan was 580 days (range, 2 months to 11 years).
CDM
All patients underwent a work-up with CDM, including an abdominal CT scan and a chest x-ray. Depending on the specific clinical problem, other appropriate investigations were also performed: plasma carcinoembryonic antigen (CEA) measurement (n = 81), chest CT scan (n = 42), endoscopy (n = 52), transrectal endoscopic ultrasonography (TREUS) (n = 25), and magnetic resonance imaging of the liver (n = 20).
PET
Whole-body FDG-PET scans were performed within 2 months of CDM, using a CTI Siemens ECAT 931 tomograph (Siemens-CTI, Knoxville, TN). This tomograph has a 10.1-cm z-axis field of view and 15 image planes spaced 6.75 mm apart. All patients fasted for at least 6 hours before FDG-PET scanning. A dose of 370 to 550 MBq [18F]FDG was administered intravenously as a bolus. After tracer injection, patients were kept well hydrated and received a diuretic to minimize image artifacts from urinary stasis in the renal collecting system and ureters. During the time between injection and scanning, patients were asked to sit or lie comfortably to avoid muscular tracer accumulation. In 29 patients who were scanned before June 1993, the bladder was continuously flushed during the acquisition via a triple lumen catheter. Patients scanned thereafter were not catheterized, because at that time iterative reconstruction algorithms, which are less sensitive to reconstruction artifacts from hyperactive areas such as the urinary bladder, became available for routine use. Imaging was started after a 60-minute uptake period. Images of 10 longitudinally sequential bed positions were acquired so that the total effective z-axis field of view extended from the patient's head to the upper third of the thighs. Each bed position was imaged for 4 minutes. All FDG-PET images were reconstructed with use of an iterative reconstruction algorithm and 32 iterations.11,12 Attenuation correction could not be performed for technical reasons.
Data Analysis
Transaxial, coronal, and sagittal views of the emission scans were evaluated by visual inspection on a high-resolution display monitor (Sun workstation; Sun Microsystems, Inc, Mountain View, CA) by two experienced nuclear medicine physicians. At the time of the interpretation, the observers were fully aware of the results of the CDM studies but completely blinded to the final outcome of the patient. Areas of marked focal FDG accumulation greater than the background activity of the examined organ were interpreted as sites of malignant disease. Equivocal FDG-PET readings were classified as negative. The results of conventional diagnostic tests were drawn from the patient's records.
Suspected lesions identified by one of the CDM studies or FDG-PET were grouped into four regions: locoregional (ie, the operative site), abdominal cavity (including mesenteric, peritoneal, and retroperitoneal metastases), liver (divided into right and left lobe), and extra-abdominal organs.
Region-based analysis.
For every region, the concordance between CDM and FDG-PET findings was verified. In the case of a discordance, the FDG-PET result was compared with the true lesion status, obtained by histopathology or clinical follow-up of more than 12 months, and classified as a true-positive, false-positive, true-negative, or false-negative result. Then, the additional value of FDG-PET imaging on regional diagnosis was calculated as the ratio of the sum of correct FDG-PET discordances to the total number of regions and expressed as a percentage.
Patient-based analysis.
Six patient subsets were defined: (1) resectable local recurrence; (2) resectable recurrence limited to one lobe of the liver; (3) extended disease: inoperable patients with lesions in more than one region, with bilobar liver metastasis, or with abdominal lymph node metastasis; (4) completely normal CDM findings despite clinical suspicion of recurrent disease; (5) elevated plasma CEA levels with otherwise normal CDM findings; and (6) inconclusive CDM findings. The diagnostic impact of performing an additional FDG-PET scan on staging of the patient's disease was assessed by verifying the discordances between CDM and FDG-PET according to this patient classification. On the basis of the true patient status, obtained by histopathology or clinical follow-up of more than 12 months, the discordant FDG-PET results were categorized as correctly upstaging, correctly downstaging, falsely overstaging, or falsely understaging the patient's disease. Then, the additional value of FDG-PET imaging on disease staging was calculated as the ratio of the sum of correct FDG-PET discordances to the total number of patients and expressed as a percentage.
Statistical Analysis
The relative number of true and false discordant results between whole-body FDG-PET and the CDM was compared by a McNemar test for correlated proportions.
RESULTS
Region-Based Analysis
Table 1 shows the distribution of the discordances between CDM and FDG-PET per anatomic region and the methodology used to define the true lesion status. A total of 40 regional discordances were found in 103 patients. The true lesion status of these discordances was determined by histologic examination in 22 cases (55%) and by follow-up in 18 cases (45%). The results of the analysis of the discordances between CDM and FDG-PET findings in the different anatomic regions are summarized in Table 2.
Distribution of Discordances Between CDM and FDG-PET Scan Readings per Anatomic Region and Methods Used to Define the True Lesion Status
Region-Based Analysis of Discordances Between CDM and FDG-PET
Locoregional recurrence.
The prevalence of locoregional recurrence among the studied patient population was 35 of 103 patients (34%). The overall diagnostic concordance rate between CDM and FDG-PET for the detection of locoregional recurrence was 84%. Overall, an additional diagnostic value of FDG-PET was found in 14 patients (14%), equally distributed among true-positives and true-negatives. The majority of discordances were found in the patient subgroup with equivocal CDM findings (n = 11), in whom FDG-PET yielded additional value in eight of the lesions. On the other hand, false-negative FDG-PET discordances were found in only two patients, both having equivocal abnormalities on CDM. One patient had an equivocal presacral mass on CT with only a late clinical manifestation of a local recurrence after 8 months; the second patient was shown on CT to have a lesion at the anastomosis that was less than 1 cm in diameter. The additional value of the FDG-PET scan for the evaluation of local recurrence was statistically significant (P = .006). In the subset of patients (n = 25) who underwent both TREUS and CT scanning, the additional diagnostic value of FDG-PET for the detection of pelvic tumor recurrence fell from 14 of 25 patients (56%) if only the CT scan was considered, to five of 25 patients (20%) if both the CT scan and TREUS were considered (Table 3). This observation is paralleled by a decrease in equivocal readings from 11 to three patients.
Additional Value of FDG-PET in 25 Patients Who Underwent a CT Scan as Well as a TREUS, Considering CT Scan and CT Scan + TREUS Separately
Liver metastasis.
The prevalence of liver metastasis among the studied patient population was 45 of 103 patients (45%). The overall concordance rate was 93%. Additional diagnostic FDG-PET value was found in six of 103 patients (6%). All patients with inconclusive CDM findings (n = 3) in the liver were correctly classified by FDG-PET as true-positive (n = 2) or true-negative (n = 1). An incorrect discordant FDG-PET result was found in one patient with normal homogeneous hepatic FDG uptake in spite of multiple small (< 1 cm) metastases in both lobes, as found by laparoscopy. We found no additional value of FDG-PET in the case of completely normal results with CT and/or magnetic resonance imaging of the liver. Furthermore, there were no false-positives. Overall, the additional value of FDG-PET for the evaluation of liver metastasis was statistically not significant, owing to the small number of patients with discordant findings.
Abdominal cavity.
The prevalence of extrahepatic abdominal metastases among the studied patient population was 20 of 103 patients (19%). The lesions were located in retroperitoneal lymph nodes (n = 10), the peritoneal space (n = 6), or both (n = 4). Overall, the concordance rate was 91%. Additional diagnostic FDG-PET value was found in seven patients (7%), predominantly based upon true-positive FDG-PET findings in CDM-negative patients. Interestingly, five of these six true-positive lesions were located in the peritoneum. One false-positive FDG-PET discordance was located in the right abdominal fossa. A colonoscopy reported the presence of a focal area of colitis, which was probably responsible for the increased FDG accumulation. The additional value of FDG-PET in this anatomic area did not reach statistical significance, owing to the small number of patients with discordant findings.
Extra-abdominal metastasis.
The prevalence of extra-abdominal metastasis among the studied patient population was 17 of 103 patients (17%). CDM detected extra-abdominal disease in eight patients. FDG-PET findings were concordant in all of these sites. In the patients with negative extra-abdominal CDM staging, FDG-PET detected previously unsuspected lesions in nine patients. Of these, eight lesions were true-positive FDG-PET results located in the lungs (n = 5), axilla (n = 1), neck (n = 1), and skull (n = 1). Of the five lung lesions, the CT scan of the thorax was false-negative in two and was not performed in three. One false-positive discordant FDG-PET lesion in the right lung was reported in a patient with underlying inflammatory lung disease. The additional value of the FDG-PET scan for the evaluation of extra-abdominal metastasis was statistically significant (P = .006).
Patient-Based Analysis
The additional value of FDG-PET in patient classification is summarized in Table 4. In the patient subgroup with presumed resectable solitary liver metastasis (n = 37), the FDG-PET scan correctly upstaged the classification of four patients to an inoperable, extended-disease stage. The additionally detected tumor sites were located in retroperitoneal lymph nodes (n = 1), the contralateral liver lobe (n = 1), a lung (n = 1), and the base of the skull (n = 1). One patient's classification was incorrectly overstaged to an extended-disease stage by FDG-PET owing to a false-positive lesion in the abdominal cavity. Subsequent colonoscopy identified focal colitis in that region that was probably responsible for the increased FDG accumulation. In this patient subgroup, additional diagnostic value of FDG-PET was found in four of 37 patients (11%).
Patient-Based Analysis of Disconcordance Between CDM and FDG-PET
In the patient subgroup with presumed resectable locoregional recurrence (n = 23), a discordant FDG-PET status was found in eight patients. Additional diagnostic value of FDG-PET was found in eight of 23 patients (35%), based on the detection of additional unsuspected tumor sites in five patients and the exclusion of recurrent disease activity in three patients. The additional true-positive tumor sites detected by FDG-PET were located in the axilla (n = 1), abdominal cavity (n = 2), and lungs (n = 2). An example of the additional value of FDG-PET in a patient with presumed limited pelvic recurrence is shown in Fig 1.
Additional value of FDG-PET scan in a patient with presumed resectable locoregional recurrence. PET demonstrated the presence of a local recurrence (plain arrows) and an unsuspected lesion at the right lung hilus (dashed arrows). Radiologic follow-up of the lesion confirmed the presence of a metastasis.
A third patient subgroup consisted of 22 patients with extended disease, documented by conventional imaging techniques, who were not eligible for curative surgery. In these patients, a discordant FDG-PET result was found in only two patients; FDG-PET result was true in one patient and false in the other. The latter patient's classification was incorrectly downstaged by FDG-PET owing to a normal FDG distribution in the liver despite the presence of bilobar metastases. The other patient's classification was correctly downstaged by FDG-PET because of a true-negative FDG-PET finding in the pelvis; the patient was thus classified as having an operable solitary liver metastasis. Thus, in this patient subgroup, FDG-PET imaging did not yield significant additional diagnostic information.
A fourth subset of patients consisted of eight patients with completely normal CDM findings. In these patients, FDG-PET did not detect any additional tumor site. They all remained tumor-free during follow-up (range, 12 to 39 months).
In another patient subgroup (n = 8), the only indicator for recurrent disease activity was an elevated plasma CEA level (mean, 38 ng/mL; range, 9 to 56 ng/mL; normal range, 0 to 2.5 ng/mL). All conventional imaging studies were negative. FDG-PET correctly detected tumor recurrence in three of these patients. The lesions were located in the liver, at the postsurgical site in the pelvis, and in a neck lymph node. In this subgroup, one false-positive FDG-PET lesion was reported in the lung on the basis of FDG uptake in a tuberculotic lesion. During follow-up of the patients with normal FDG-PET findings, one patient remained tumor-free (follow-up, 48 months), two patients had a local recurrence, and one patient developed diffuse peritoneal metastasis 8 months later.
A last patient subgroup consisted of five patients whose only abnormal CDM sign was an equivocal CT scan reading at the postsurgical site in the pelvis (n = 4) or in the liver (n = 1). FDG-PET correctly classified these findings as true-negative in two patients and true-positive in three patients.
In terms of patient management, these subgroups can be regrouped into three patient categories. The first category consists of 60 patients in whom, on the basis of CDM findings, surgical resection of the locoregional or liver recurrences could be considered. In this category, additional FDG-PET value was found in 12 of 60 patients (20%). The additional value of FDG-PET in this patient subset was statistically significant (P = .006). A second category consists of 13 patients with inconclusive CDM findings or with elevated CEA plasma levels with normal conventional imaging results. Additional FDG-PET value was found in eight of 13 patients (62%). The additional value of FDG-PET in this patient subset was statistically significant (P = .045). A third category consists of eight patients with a clinical suspicion of recurrent disease but with completely normal CDM findings and 22 patients in whom CDM detected an extended-disease stage. FDG-PET scanning did not offer additional diagnostic information in these latter categories.
DISCUSSION
This study confirms the significant role for whole-body FDG-PET imaging as a complementary diagnostic modality to conventional staging techniques in the follow-up of patients with resected colorectal adenocarcinoma. Major areas in which FDG-PET had a particular positive impact on diagnosis were the biochemical characterization of lesions that are indeterminate on anatomic imaging, the selection of patients most likely to benefit from surgical resection of recurrences, and the localization of occult metastatic disease.
One of the main applications of FDG-PET in recurrent colorectal cancer patients has been the biochemical characterization of pelvic lesions that are indeterminate on structural imaging procedures, such as CT or magnetic resonance imaging.13,14 Most of these studies have relatively small numbers of patients, but in all studies, the sensitivity and specificity of FDG-PET imaging were very high and better than those of CT, magnetic resonance imaging, or radioimmunoscintigraphy. Our study specifically addressed the concordance of FDG-PET with the referring clinician's diagnosis inferred from the integrated data of the physical examination, plasma CEA monitoring, CT scan, endoscopy, and TREUS. From this point of view, a true-discordant FDG-PET diagnosis was found in 14% of the patients, which is significantly lower than expected from the literature. This could be explained by more extensive and accurate CDM studies, including high-quality spiral CT scan and TREUS, although a formal comparison with CDM performed in several centers is not feasible. The major part of the additional value of FDG-PET in this situation resided in the subgroup of patients with inconclusive CDM findings and consisted in a significant decrease of equivocal FDG-PET readings compared with the CDM. This is illustrated by the fact that if TREUS is part of the CDM, it reduces the additional diagnostic value of FDG-PET in parallel to a dramatic decrease of equivocal reports. In the subset of patients (n = 25) who underwent both TREUS and CT scanning, the additional diagnostic value of FDG-PET for the detection of pelvic tumor recurrence fell from 56% if only the CT scan was considered, to 20% if the CT scan and TREUS were considered together. Several reports have indeed advocated TREUS as a more effective noninvasive technique than CT for the detection of local recurrences of rectal carcinoma in the pelvis.15-17 However, a direct comparison of the efficacy of TREUS versus FDG-PET has not been reported.
Locoregional pelvic recurrence and liver metastases are the major sites of relapse after resection of colorectal cancer. Surgical resection is the only curative therapy in these patients, but recurrence is frequent, and considerable mortality and morbidity have been reported. Therefore, before these major surgical interventions are embarked on, it is imperative that there be no disease outside the operation field. The conventional imaging modality of choice for evaluating these patients is the CT scan, which is relatively sensitive for detecting liver metastases but less so for lymph node metastases and mesenteric involvement. Moreover, the limited field of view can lead to the overlooking of unsuspected metastatic lesions outside the abdomen and thorax. In this study, 60 patients were considered for surgical resection of presumed solitary recurrent local or hepatic disease, on the basis of the findings of a complete conventional work-up. Adding FDG-PET imaging in this patient group potentially changed the therapeutic management in 12 patients (20%) by correctly upstaging the classification of nine patients to an inoperable, extended-disease stage and by correctly downstaging the classification of three patients to a disease-free status. These findings are in good agreement with recently published data of Delbeke et al,5 who reported a change in surgical management in 28% of the 52 studied patients. More successful results of the FDG-PET technique in this particular setting have been reported by Lai et al,6 who detected unsuspected extrahepatic malignant disease that was missed by CDM in 32% of 34 patients. The region-based analysis indicated that the beneficial impact of FDG-PET on disease staging mainly results from a significant additional diagnostic accuracy for the diagnosis of locoregional recurrence, from a higher sensitivity for abdominal lymph node metastasis, and from the detection of unsuspected extra-abdominal metastatic sites. Our study therefore shows a definite potential of FDG-PET for improving patient selection and reducing inappropriate surgical interventions.
The potential benefit of FDG-PET is particularly appealing in the recurrent colorectal cancer patient with a rising CEA who has a negative conventional work-up. Several studies have independently demonstrated the high accuracy of FDG-PET in localizing the source of recurrence in patients with occult disease based on elevated CEA serum levels. Valk et al18 reported true-positive FDG-PET findings in 70% of 27 patients with CEA elevation and a normal CT scan. In our study, 57 patients had elevated CEA levels; only eight (14%) of these patients had normal CDM findings, suggesting the relative rarity of this clinical situation. FDG-PET correctly localized metastatic sites in three patients but was false-positive in one of them. These findings indeed suggest a significant additional value of FDG-PET imaging in such patients. However, larger prospective and multicenter studies are needed to confirm the role of FDG-PET imaging in this particular setting.
FDG is not a very tumor-specific substance, inasmuch as the leukocytes and macrophages of inflammatory processes also accumulate the tracer. This is a major source of false-positive diagnoses in the application of FDG-PET in oncology.19 Moreover, physiologic tracer activity in the normal gastrointestinal or urinary tract can sometimes mimic pathologic lesions. Nevertheless, we reported only two false-positive FDG-PET readings due to increased FDG uptake in inflammatory lesions in lungs and colon. Importantly, these two false-positive FDG-PET readings resulted in an overstaging of the classification of two patients with presumed limited and resectable recurrent disease to an extended-disease stage, possibly leading to the cancellation of potentially curative surgery. Therefore, to reduce the potentially negative impact of occasional false-positive FDG-PET results on patient management, it is absolutely mandatory to carefully select the candidates for an FDG-PET scan, excluding those with known inflammatory lung or bowel disease, to correlate closely the FDG-PET images with data from conventional imaging methods, and to carefully confirm by other means the additional FDG-PET lesions that significantly alter patient management.
A second limitation of PET is the limited spatial resolution of the imaging tool, leading to false-negative reports in small lesions. Importantly, three of the four false-negative discordant PET findings in our study were indeed small-volume tumors (< 1 cm in diameter). This finding indicates that the limited spatial resolution of the imaging method, rather than an insufficient tracer concentration in the tumor, is the major reason for the nonvisualization of these lesions. It is clear that future technologic innovations that optimize the spatial resolution of the PET systems will significantly increase the additional diagnostic value of PET imaging in staging of recurrent colorectal cancer. The observation that false-negative FDG-PET findings are due to resolution rather than metabolic constraints again emphasizes the importance of having a detailed knowledge of the morphologic and structural characteristics of the suspected tumor before excluding tumor recurrence on the basis of FDG-PET scan findings.
A major criticism of the current study could be the retrospective character and the interpretation of the PET images with a priori knowledge of results of the conventional diagnostic procedures. However, the purpose of this study was to assess the diagnostic yield of FDG-PET in addition to the CDM in different patient subsets. For this, we specifically focused on the discordances between both modalities to characterize the type of patients that would most likely benefit from performing an additional PET scan after a set of conventional investigations. Differences in sensitivity or specificity between CDM and FDG-PET or the value of FDG-PET as a first-line screening technique can only be inferred from a prospective study with blinded readings.
A second limitation of this study could be the methodology to define the true lesion status of the discordances. Whereas it would have been ideal to have a histologic diagnosis of all discordant lesions, 22 (55%) of 40 lesions were determined only by clinical follow-up. In our opinion, the possibility that this had a significant impact on the results and conclusions is very small, mainly because a minimal follow-up of 12 months was required. A relapse of a colorectal carcinoma, once present, is usually a relatively fast-evolving tumor. It is known that the median survival of patients with advanced or metastatic colorectal cancer is 6 months. Therefore, it would be extremely unusual that metastases did not progress over the period of 1 year, especially when the masses were evaluated by means of a CT scan. However, a possible error in the true lesion status could occur when a nonsurgical antineoplastic therapy was initiated in a patient with a positive or equivocal CDM and a negative PET result. Under these circumstances, a slower tumor progression could indeed have led to a false-negative instead of a true-negative FDG-PET discordance. In our study, this potential bias was of marginal importance, as this particular condition was found only once, in a patient with extended recurrent cancer who had a positive CDM and a negative PET finding in the liver. Palliative chemotherapy was initiated, but a follow-up CT scan showed a fulminatory progression of the extrahepatic recurrences, whereas the hepatic lesions remained unchanged and were at that moment interpreted as benign biliary cysts.
In conclusion, significant additional diagnostic value of FDG-PET performed in conjunction with CDM was found in 20% of patients with presumed resectable hepatic or pelvic recurrence, as well as in 62% of patients with inconclusive CDM findings or with elevated plasma CEA levels with a normal work-up. The region-based analysis indicates that the beneficial impact of FDG-PET on disease staging mainly results from a significant positive impact of FDG-PET in the case of inconclusive CDM findings in the pelvis, from a higher sensitivity for abdominal lymph node metastasis, and from the detection of unsuspected extra-abdominal metastatic sites.
Footnotes
-
Presented in part at the Annual Meeting of the American Society of Clinical Oncology, Los Angeles, CA, May 1998.
- Received July 22, 1998.
- Accepted November 20, 1998.
