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DOI: 10.1148/radiol.2453061538
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(Radiology 2007;245:839-847.)
© RSNA, 2007

Nuclear Medicine

Bone and Soft-Tissue Sarcoma: Preoperative Staging with Fluorine 18 Fluorodeoxyglucose PET/CT and Conventional Imaging1

Ukihide Tateishi, MD, Umio Yamaguchi, MD, Kunihiko Seki, MD, Takashi Terauchi, MD, Yasuaki Arai, MD, and E. Edmund Kim, MD

1 From the Division of Diagnostic Radiology (U.T., Y.A.), Division of Orthopedic Oncology (U.Y.), and Clinical Laboratory (K.S.), National Cancer Center Hospital, Tokyo, Japan; Division of Cancer Screening, Research Center for Cancer Prevention and Screening, National Cancer Center, Tokyo, Japan (T.T.); and Division of Diagnostic Imaging, University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Blvd, Unit 1264, Houston, TX 77030 (U.T., E.E.K.). Received September 5, 2006; revision requested November 10; revision received November 20; accepted January 8, 2007; final version accepted April 2. Supported in part by grants from Scientific Research Expenses for Health and Welfare Programs, No. 17-12, the Promotion and Standardization of Diagnostic Accuracy in PET/CT Imaging, the Grant-in-Aid for Cancer Research from the Ministry of Health, Labor and Welfare, and a Travel Grant from the Princess Takamatsu Cancer Research Fund. Address correspondence to U.T. (e-mail: utateish{at}ncc.go.jp).


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
 IMPLICATION FOR PATIENT CARE
 References
 
Purpose: To retrospectively compare the diagnostic accuracy of positron emission tomography (PET)/computed tomography (CT), PET, conventional imaging, and combined PET/CT and conventional imaging for tumor staging of bone and soft-tissue sarcomas, by using histologic or follow-up imaging findings as the reference standard.

Materials and Methods: Institutional review board approval was received for this HIPAA-compliant study; informed consent was obtained. Integrated PET/CT was performed in 117 patients (69 male patients, 48 female patients; mean age, 42 years ± 21 [standard deviation]; range, 9–86 years). Conventional imaging consisted of magnetic resonance imaging of the primary site, chest radiography, whole-body contrast material–enhanced CT, and bone scintigraphy. A total of four reviewers assessed all images. Overall and T staging were evaluated in 69 (59%) patients who underwent surgical removal of the primary tumors and had pathologically proved results. N and M staging were evaluated in all patients, and their reference methods were based on histologic findings (n = 101) and follow-up CT findings (n = 16).

Results: Interpretations based on combined PET/CT and conventional imaging findings correctly staged tumors in 60 (87%) of 69 patients, overstaged tumors in eight (12%) patients, and understaged tumors in one (1%) patient. Overall staging accuracy of combined PET/CT and conventional imaging was significantly higher than that at PET (P < .0001). Combined PET/CT and conventional imaging resulted in correct N staging in 114 (97%) of 117 patients and M staging in 109 (93%) of 117 patients. Combined PET/CT and conventional imaging helped reduce overstaging in three (4%) patients and helped change tumor diagnosis from unresectable to resectable in two (2%) patients compared with PET/CT.

Conclusion: The combination of PET/CT and conventional imaging is accurate in preoperative staging of bone and soft-tissue sarcoma.

© RSNA, 2007


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
 IMPLICATION FOR PATIENT CARE
 References
 
Histologic grade is incorporated into the staging classification of bone and soft-tissue sarcomas because the biologic behavior of bone and soft-tissue sarcomas depends on the histologic grade. The prognostic importance of histologic type and grading and staging systems for bone and soft-tissue sarcomas has been investigated previously in a large series (1–3).

The diagnostic tools for staging bone and soft-tissue sarcomas are clinical examination, magnetic resonance (MR) imaging and radiography of the primary tumor site, chest radiography or computed tomography (CT), and bone scintigraphy (4). Fluorine 18 fluorodeoxyglucose (FDG) positron emission tomography (PET) has been shown to be useful for detection of nodal and distant metastases in patients with soft-tissue sarcomas compared with that at conventional imaging (5–7).

There are substantial differences in FDG uptake values between low- and high-grade bone and soft-tissue sarcomas (8–10). Uptake values of FDG have been shown to correlate with histologic grade in heterogeneous series of bone and soft-tissue sarcomas (11,12). PET/CT can help improve the localization of tumors and the accuracy of staging in patients with bone and soft-tissue sarcoma (13). However, despite the increasing use of FDG PET/CT in the management of bone and soft-tissue sarcomas, to our knowledge, no study to date has assessed the diagnostic accuracy of preoperative staging with PET/CT, PET, and conventional imaging. Thus, the aim of our study was to retrospectively compare the diagnostic accuracy of PET/CT, PET, conventional imaging, and combined PET/CT and conventional imaging for the evaluation of locoregional tumor extent and detection of nodal and distant metastases of bone and soft-tissue sarcomas, by using histologic or follow-up imaging findings as the reference standard.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
 IMPLICATION FOR PATIENT CARE
 References
 
Patients
Eligible patients had a newly diagnosed tumor that was strongly suspected of being a bone or soft-tissue sarcoma. Patients were questioned about the presence of three symptoms: induration, tenderness, and numbness. The inclusion criteria for the performance status were a performance status of 0 (fully active and able to perform all predisease activities without restriction) or 1 (restricted in physically strenuous activity but ambulatory and able to perform work of a light or sedentary nature) (14). Exclusion criteria were hematologic malignancy, uncontrolled diabetes, and pregnancy or lactation. Institutional review board approval was received for this Health Insurance Portability and Accountability Act–compliant study after all patients provided their informed consent for the review of their records and images.

A total of 129 patients clinically suspected of having a bone or soft-tissue sarcoma underwent PET/CT and conventional imaging, but 12 did not meet the criteria (Fig 1). In two of 12 patients, diabetes was uncontrolled. Ten of 12 patients were excluded because they had benign bone or soft-tissue lesions or hematologic malignancies (inflammatory change [n = 4], plasmacytoma [n = 3], malignant lymphoma [n = 2], or Schwannoma [n = 1]). The remaining 117 patients (69 male patients, 48 female patients; mean age, 42 years ± 21 [standard deviation]; age range, 9–86 years) were included in our study.


Figure 1
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  		Figure 1: Diagram of patients enrolled according to study protocol.

 
PET/CT Imaging
Scans were acquired with a PET/CT device (Aquiduo; Toshiba Medical Systems, Tokyo, Japan) that consisted of a PET scanner (ECAT HR+; CTI, Knoxville, Tenn) and a 16-section CT scanner (Aquilion V-detector; Toshiba Medical Systems) with a whole-body mode implemented as the standard software. Before the FDG PET/CT study, patients fasted for at least 6 hours. All patients were tested for a normal glucose level (range, 80–120 mg/dL [4.4–6.7 mmol/L]) before PET scanning. CT was performed from the head to the leg according to a standardized protocol with the following settings: transverse 3.0-mm collimation x 16 modes, 120 kVp, 100 mAs, 0.5-second tube rotation, and 11.0-mm/sec table speed. No intravenous or oral contrast material was administered. Emission scans from the base of the skull to the leg were obtained, starting 60 minutes after intravenous administration of 300–370 MBq of FDG. Acquisition time for PET scans was 2 minutes per table position. Images were reconstructed with attenuation-weighted ordered-subset expectation maximization with two iterations and eight subsets by using emission scans and CT data.

Conventional Imaging
Conventional imaging methods, performed within 2 weeks of PET/CT (either before or after), were technetium 99m (99mTc)-hydroxymethylene diphosphonate (HMDP) bone scintigraphy, chest radiography, whole-body CT, and MR imaging of the primary site. A dual-headed gamma camera (E.CAM; Siemens, Knoxville, Tenn) was used to perform 99mTc-HMDP bone scintigraphy. All chest radiographs were acquired at 100 kV with a computed radiographic system (Toshiba Medical Systems). Whole-body CT was performed by using a multidetector scanner (Aquilion V-detector; Toshiba Medical Systems) with the following settings: transverse 4.0-mm x four modes, 120 kVp, automated electric current, 0.5-second tube rotation, and 5.0-mm/sec table speed. Images were reconstructed with 10.0-mm section thickness by using a standard algorithm. Intravenous contrast material was administered in all patients. A total of 100 mL of contrast material (iopamidol, Oiparomin 370; Konica Minolta, Tokyo, Japan) was administered intravenously by using an autoinjector (Autoenhance A250; Nemoto Kyorindo, Kyoto, Japan) at a rate of 2.0 mL/sec. Scan delay was set at 60 seconds after injection of contrast material. No oral contrast material was administered. MR imaging of the primary site was performed by using a 1.5-T system (Signa Horizon, GE Medical Systems, Milwaukee, Wis; or Visart, Toshiba Medical Systems). Pulse sequences comprised T1-weighted spin echo or fast spin echo, T2-weighted fast spin echo, and postcontrast T1-weighted spin echo imaging with fat suppression after injection of 0.1 mmol per kilogram of body weight of gadopentate dimeglumine (Magnevist; Schering, Berlin, Germany).

Image Interpretation
Each tumor was staged according to the TNM classification of the International Union Against Cancer for sarcoma of bone and according to the American Joint Committee on Cancer staging protocol for sarcoma of soft tissue (15,16). T, N, and M stages were assigned at PET/CT, PET, conventional imaging, and combined PET/CT and conventional imaging. One radiologist (U.T., with 12 years of experience) and one nuclear medicine specialist (T.T., with 18 years of experience) reviewed conventional images, PET images, and PET/CT images in consensus. The sequence of image interpretation was conventional images, PET images, and PET/CT images, and the interval between each interpretation was 2 weeks. Combined PET/CT and conventional images were evaluated in consensus by one radiologist and one nuclear medicine specialist (Y.A. and E.E.K., respectively, each with more than 20 years of experience). Qualitative evaluation of focally increased glucose metabolism, as well as quantitative evaluation of maximum standardized uptake values, was performed. Standardized uptake value was normalized for body weight.

PET and coregistered PET/CT images were analyzed with dedicated software (Syngo; Siemens). The initial review of the attenuation-corrected PET images was performed by using transverse, coronal, and sagittal planes. Abnormal FDG uptake was defined as uptake higher than the background activity in the soft tissue. A pixel region of interest was outlined within regions of increased FDG uptake and was measured on each section. When the tumor was extensively heterogeneous, the regions of interest were set to include the entire tumor.

Reference Standard
The assessment of overall TNM staging and T staging was based on findings in 69 patients for whom the T stage was verified histologically by using specimens obtained at surgical resection of primary tumors. Evaluation of N staging was based on findings in 117 patients in whom N staging was confirmed with histologic examination of specimens obtained at nodal dissection or sampling (n = 88), CT-guided needle biopsy (n = 13), and/or an obvious progression in number and/or size of the lesion at follow-up CT (n = 16; mean follow-up period, 106 days). Verification of M staging was accomplished in 117 patients by means of radiologic follow-up (n = 107; mean follow-up period, 95 days) or CT-guided needle biopsy (n = 10). All radiologic examinations were performed within 2 weeks (mean, 6 days) before surgical procedure or biopsy.

Statistical Analysis
All variables were assessed on a patient-by-patient basis. The McNemar test was used for paired comparisons between conventional imaging, PET, PET/CT, and combined PET/CT and conventional imaging. Bonferroni correction was applied for McNemar test values adjusted for the number of comparisons between conventional imaging, PET, PET/CT, and combined PET/CT and conventional imaging. Six pairs of imaging methods were compared for T, N, M, and overall staging. We reported the standard McNemar P value and considered each to indicate a significant difference if P was less than or equal to .0083 (.05 divided by 6, the number of comparisons). All P values are two sided. Statistical analysis was performed with software (SPSS, version 11; SPSS, Chicago, Ill).


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 ADVANCES IN KNOWLEDGE
 IMPLICATION FOR PATIENT CARE
 References
 
Patients
Pathologically confirmed T stages included T1 (n = 3), T2 (n = 17), and T3 (n = 1) in bone tumors and T1a (n = 2), T1b (n = 8), T2a (n = 2), and T2b (n = 36) in soft-tissue tumors. Median tumor size was 9.2 cm (range, 1.0–26.0 cm). Tumor grades were similar with regard to age, sex, tumor size, and tumor location (Table 1).


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  		Table 1. Demographic Data and Tumor Stage and Diagnosis

 
T Staging
The T stage was correctly determined in 66 (96%) of 69 patients by using PET/CT (Table 2, Fig 2). False-positive findings in three patients were caused by misdiagnosis of minimally invasive deep tumors. The T stage was correctly determined in 55 (80%) patients by using PET alone and in 65 (94%) patients by using conventional imaging alone. On the basis of combined PET/CT and conventional images, the T stage was correctly determined in 68 (99%) patients. A false-positive finding was found for one superficial tumor that was misdiagnosed as a deep tumor. Differences in accuracy were not significant between conventional imaging and PET/CT (P > .999), between conventional imaging and combined PET/CT and conventional imaging (P = .250), and between PET/CT and combined PET/CT and conventional imaging (P = .500), while differences in accuracy between PET/CT and PET (P = .001), between conventional imaging and PET (P = .002), and between PET and combined PET/CT and conventional imaging (P < .0001) were significant.


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  		Table 2. Values for T Staging with Different Modalities

 

Figure 2A
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  		Figure 2a: Transverse images in 16-year-old adolescent boy with osteosarcoma in tibia. (a) CT image of leg shows mineralized primary tumor (arrow) in right tibia. (b) FDG PET image of leg shows abnormal uptake in tibia. (c) Integrated PET/CT image shows FDG uptake in right tibia, which corresponds to primary site at level similar to that on a and b. Numbers = color scale from software.

 

Figure 2B
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  		Figure 2b: Transverse images in 16-year-old adolescent boy with osteosarcoma in tibia. (a) CT image of leg shows mineralized primary tumor (arrow) in right tibia. (b) FDG PET image of leg shows abnormal uptake in tibia. (c) Integrated PET/CT image shows FDG uptake in right tibia, which corresponds to primary site at level similar to that on a and b. Numbers = color scale from software.

 

Figure 2C
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  		Figure 2c: Transverse images in 16-year-old adolescent boy with osteosarcoma in tibia. (a) CT image of leg shows mineralized primary tumor (arrow) in right tibia. (b) FDG PET image of leg shows abnormal uptake in tibia. (c) Integrated PET/CT image shows FDG uptake in right tibia, which corresponds to primary site at level similar to that on a and b. Numbers = color scale from software.

 
N Staging
Nodal metastasis (Fig 3) was identified in 17 (15%) patients with soft-tissue tumors (Table 3). N staging with PET/CT was correct in 112 (96%) patients. False-positive findings in three patients were caused by reactive lymph nodes. False-negative findings in two patients resulted from subcentimetric lymph nodes, which did not show abnormal FDG uptake. The diameters of these lymph nodes in the long axis were 6 and 8 mm. Determination of lymph node involvement on the basis of PET data alone resulted in 109 (92%) correctly staged tumors. Lymph node involvement was correctly determined in 106 (91%) patients on the basis of conventional images. False-positive findings in three patients were caused by reactive lymph nodes. N staging was correctly determined in 114 (97%) patients by using combined PET/CT and conventional imaging. There was one patient with a false-positive finding caused by a reactive lymph node and two patients with false-negative findings that resulted from subcentimetric lymph nodes. The sizes of these lymph nodes in the long axis were 6 and 8 mm. A significant difference was found only between conventional imaging and combined PET/CT and conventional imaging (P = .008).


Figure 3A
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  		Figure 3a: Transverse images in 72-year-old woman with pleomorphic malignant fibrous histiocytoma of buttock. (a) Integrated PET/CT image of pelvis shows abnormal FDG uptake in deep soft-tissue mass of buttock (arrow). (b) CT image of thigh shows slight swelling of soft tissue. (c) FDG PET image of right thigh shows abnormal uptake in soft tissue of right thigh (arrow). (d) Integrated PET/CT image of thigh shows that abnormal uptake in right thigh corresponds to lymph node metastasis involving surrounding soft tissue at level similar to that on b and c (arrow).

 

Figure 3B
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  		Figure 3b: Transverse images in 72-year-old woman with pleomorphic malignant fibrous histiocytoma of buttock. (a) Integrated PET/CT image of pelvis shows abnormal FDG uptake in deep soft-tissue mass of buttock (arrow). (b) CT image of thigh shows slight swelling of soft tissue. (c) FDG PET image of right thigh shows abnormal uptake in soft tissue of right thigh (arrow). (d) Integrated PET/CT image of thigh shows that abnormal uptake in right thigh corresponds to lymph node metastasis involving surrounding soft tissue at level similar to that on b and c (arrow).

 

Figure 3C
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  		Figure 3c: Transverse images in 72-year-old woman with pleomorphic malignant fibrous histiocytoma of buttock. (a) Integrated PET/CT image of pelvis shows abnormal FDG uptake in deep soft-tissue mass of buttock (arrow). (b) CT image of thigh shows slight swelling of soft tissue. (c) FDG PET image of right thigh shows abnormal uptake in soft tissue of right thigh (arrow). (d) Integrated PET/CT image of thigh shows that abnormal uptake in right thigh corresponds to lymph node metastasis involving surrounding soft tissue at level similar to that on b and c (arrow).

 

Figure 3D
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  		Figure 3d: Transverse images in 72-year-old woman with pleomorphic malignant fibrous histiocytoma of buttock. (a) Integrated PET/CT image of pelvis shows abnormal FDG uptake in deep soft-tissue mass of buttock (arrow). (b) CT image of thigh shows slight swelling of soft tissue. (c) FDG PET image of right thigh shows abnormal uptake in soft tissue of right thigh (arrow). (d) Integrated PET/CT image of thigh shows that abnormal uptake in right thigh corresponds to lymph node metastasis involving surrounding soft tissue at level similar to that on b and c (arrow).

 

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  		Table 3. Values for N Staging with Different Modalities

 
M Staging
Verification of distant metastatic disease (n = 48, 41%) was accomplished with radiologic follow-up in 12 patients and with biopsy in 36 patients. Determination of distant metastases with PET/CT was correct in 107 (91%) patients (Table 4). False-positive findings in six patients resulted from redundant primary tumor (n = 4), small bone metastasis (n = 1), and multicentric bone tumor (n = 1). Reasons for false-negative results in four patients were underestimation of bone or soft-tissue metastasis (n = 3) and redundant primary tumor (n = 1). Distant metastases were correctly determined in 106 (91%) patients with PET alone and in 93 (79%) patients with conventional imaging. Combined PET/CT and conventional imaging helped correctly determine M staging in 109 (93%) patients. In six patients, false-positive findings resulted from redundant primary tumor (n = 4), small bone metastasis (n = 1), and multicentric bone tumor (n = 1). There were two patients with false-negative findings caused by underestimation of bone or soft-tissue metastasis (n = 1) and redundant primary tumor (n = 1).


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  		Table 4. Values for M Staging with Different Modalities

 
Differences in accuracy between PET and PET/CT (P > .999), between PET and combined PET/CT and conventional imaging (P = .250), and between PET/CT and combined PET/CT and conventional imaging (P = .500) were not significant, while differences in accuracy between conventional imaging and PET (P < .0001), between conventional imaging and PET/CT (P < .0001), and between conventional imaging and combined PET/CT and conventional imaging (P < .0001) were significant.

Overall TNM Staging
The overall tumor stage was correctly classified in 53 (77%) patients when analysis was based on conventional images (Table 5). PET alone enabled accurate staging in 48 (70%) patients, whereas PET/CT enabled accurate staging in 57 (83%) patients. Combined PET/CT and conventional imaging helped determine overall stage correctly in 60 (87%) patients. Differences in the accuracy of overall tumor staging between conventional imaging and combined PET/CT and conventional imaging (P = .016), between PET and PET/CT (P = .004), and between PET and combined PET/CT and conventional imaging (P < .0001) were significant. No significant differences were found in accuracies between conventional imaging and PET (P = .063), between conventional imaging and PET/CT (P = .125), and between PET/CT and combined PET/CT and conventional imaging (P = .250).


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  		Table 5. Values for Overall Staging with Different Modalities

 
Analysis of PET/CT findings revealed that the tumor had been overstaged in 11 patients and understaged in one patient, whereas conventional imaging helped classify the tumor as overstaged in 13 patients and understaged in three patients (Table 6). This revised staging affected treatment recommendations for 14 (12%) patients. The therapy recommendation was consequently altered from resectable tumor to unresectable tumor for 15 (13%) patients and from unresectable tumor to resectable tumor for one (1%) patient by using combined PET/CT and conventional imaging compared with conventional imaging alone. Combined PET/CT and conventional imaging helped reduce overstaging of the tumor in three patients in comparison with PET/CT. This revised status for treatment changed an unresectable tumor to a resectable tumor in two (2%) patients.


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  		Table 6. Percentages of Tumors Understaged and Overstaged at TNM Staging

 
Additional Findings
False-positive findings at M staging resulted from misinterpretation of five lesions in five (4%) patients as distant metastases. These patients underwent surgical biopsy with histologic examination. Pathologic diagnoses were lung cancer (Fig 4), giant cell tumor of the bone, Schwannoma, and foreign-body granuloma. One patient who had multicentric lesions in multiple bones had a diagnosis of epithelioid hemangioendothelioma of the bone. This disease was misdiagnosed as multiple bone metastases with all modalities. One second primary tumor, which was pathologically proved to be myxoid liposarcoma, was one of the causes of false-negative results at M staging.


Figure 4A
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  		Figure 4a: Transverse images in 66-year-old woman with myxofibrosarcoma arising from lower chest wall. (a) CT image of abdomen shows ill-defined soft-tissue mass (arrows) in left lower chest wall. (b) FDG PET image of abdomen shows slight uptake in chest wall (arrows). (c) Integrated PET/CT image shows FDG uptake corresponding to ill-defined soft-tissue mass (arrows) at level similar to that on a and b. (d) Integrated PET/CT image of chest reveals pulmonary nodule (arrow) with abnormal uptake in right lung. This nodule was first diagnosed as metastasis from chest wall myxofibrosarcoma. However, this nodule was found to be primary adenocarcinoma of lung at surgical resection.

 

Figure 4B
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  		Figure 4b: Transverse images in 66-year-old woman with myxofibrosarcoma arising from lower chest wall. (a) CT image of abdomen shows ill-defined soft-tissue mass (arrows) in left lower chest wall. (b) FDG PET image of abdomen shows slight uptake in chest wall (arrows). (c) Integrated PET/CT image shows FDG uptake corresponding to ill-defined soft-tissue mass (arrows) at level similar to that on a and b. (d) Integrated PET/CT image of chest reveals pulmonary nodule (arrow) with abnormal uptake in right lung. This nodule was first diagnosed as metastasis from chest wall myxofibrosarcoma. However, this nodule was found to be primary adenocarcinoma of lung at surgical resection.

 

Figure 4C
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  		Figure 4c: Transverse images in 66-year-old woman with myxofibrosarcoma arising from lower chest wall. (a) CT image of abdomen shows ill-defined soft-tissue mass (arrows) in left lower chest wall. (b) FDG PET image of abdomen shows slight uptake in chest wall (arrows). (c) Integrated PET/CT image shows FDG uptake corresponding to ill-defined soft-tissue mass (arrows) at level similar to that on a and b. (d) Integrated PET/CT image of chest reveals pulmonary nodule (arrow) with abnormal uptake in right lung. This nodule was first diagnosed as metastasis from chest wall myxofibrosarcoma. However, this nodule was found to be primary adenocarcinoma of lung at surgical resection.

 

Figure 4D
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  		Figure 4d: Transverse images in 66-year-old woman with myxofibrosarcoma arising from lower chest wall. (a) CT image of abdomen shows ill-defined soft-tissue mass (arrows) in left lower chest wall. (b) FDG PET image of abdomen shows slight uptake in chest wall (arrows). (c) Integrated PET/CT image shows FDG uptake corresponding to ill-defined soft-tissue mass (arrows) at level similar to that on a and b. (d) Integrated PET/CT image of chest reveals pulmonary nodule (arrow) with abnormal uptake in right lung. This nodule was first diagnosed as metastasis from chest wall myxofibrosarcoma. However, this nodule was found to be primary adenocarcinoma of lung at surgical resection.

 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
ADVANCES IN KNOWLEDGE
 IMPLICATION FOR PATIENT CARE
 References
 
In our study, we demonstrated that combined PET/CT and conventional imaging helps improve the accuracy of staging bone and soft-tissue sarcomas and is important in determining the appropriate therapy. The advantage of using combined PET/CT and conventional imaging for staging bone and soft-tissue sarcomas, which is consistent with results of prior studies (17–20), is mainly due to more accurate M staging. Surgical resection would have been precluded because of combined PET/CT and conventional imaging findings in 16 (14%) patients who had distant metastases that were not identified at conventional imaging.

Because the patient population with regard to analysis of T staging was biased toward surgical candidates (n = 69, 59%), the relative accuracies of PET/CT, PET, conventional imaging, and combined PET/CT and conventional imaging could not be determined in our study. However, PET/CT, conventional imaging, and combined PET/CT and conventional imaging helped assign the T stage with a significantly higher accuracy than PET. The advantage of PET/CT with regard to T staging might be derived from CT findings, because PET cannot be adequately used to determine T stage (11–13). However, CT cannot help determine tumor invasion to adjacent structures, such as fascia, which is an essential prerequisite for the differentiation of superficial tumors from deep tumors (6). In our study, small proportions of superficial tumors (T1a or T2a: n = 4, 6%) and smaller tumors (T1: n = 13, 19%) may have resulted in accurate T staging with PET/CT, conventional imaging, and combined PET/CT and conventional imaging.

The high accuracy for N staging with all modalities is explained by the high specificity despite the small number of patients with lymph node involvement (15%). False-negative results at N staging in our study were because of small positive nodes that were missed at PET/CT, PET, conventional imaging, and combined PET/CT and conventional imaging. The false-positive interpretations of the nodes were caused by reactive lymph nodes (21,22). The small gain in accuracy for N staging in our study was because of the low frequency of nodal metastasis in bone and soft-tissue sarcomas. Lymph node dissection or sampling at wide resection is performed in all patients for N stage assessment in our institution when enlargement of a lymph node adjacent to the primary tumor is identified at conventional imaging. However, findings at combined PET/CT and conventional imaging are used to guide sampling of areas of unexpected nodal metastasis.

M staging might be one of the potential advantages of PET/CT, PET, and combined PET/CT and conventional imaging because conventional imaging alone could not help assign an M stage accurately in 24 of 48 patients with distant metastasis in our study. Five (4%) patients with false-positive results at M staging had incidental findings of importance. Of these patients, one with soft-tissue myxofibrosarcoma also had primary lung cancer. The risk of multiple malignancies in patients with soft-tissue sarcoma appears to be affected by the histologic type of myxofibrosarcoma (23). In one patient, second primary myxoid liposarcoma was one of the causes of false-negative results at M staging. Some of the findings we defined as important led to potentially lifesaving surgery because of early detection of a second primary tumor. It is possible that these findings enhance the potential value of preoperative staging.

Potential limitations of our study should be addressed. In patients with distant metastasis who were excluded from surgery on the basis of pathologic diagnosis or findings at radiologic follow-up, it was not possible to estimate T staging or overall TNM staging results because pathologic confirmation of a T stage could not be obtained. For the purposes of our study, we calculated accuracies for T staging or overall TNM staging in 69 patients and for N staging and M staging in 117 patients independently. The selection biases inherent in the choice of patients to undergo PET/CT in addition to conventional imaging should be considered. When the majority of patients have a low-grade tumor, nodal and distant metastases are less frequent. Another study limitation was the small number of patients with bone sarcoma compared with the number of patients with soft-tissue sarcoma. Although we observed a significant difference in N staging at PET/CT and combined PET/CT and conventional imaging compared with that at conventional imaging alone, this observation requires confirmation with a larger study for N-positive bone and soft-tissue sarcomas.

In summary, the overall accuracy of combined PET/CT and conventional imaging in preoperative TNM staging for patients with bone and soft-tissue sarcomas was 87%. Combined PET/CT and conventional imaging was more accurate in M staging than conventional imaging alone. Combined PET/CT and conventional imaging helped preclude surgical resection in 15 (13%) patients and helped alter treatment in 16 (14%) patients compared with conventional imaging alone. We conclude that the combination of PET/CT and conventional imaging is the best preoperative staging method for bone and soft-tissue sarcomas, because of its significantly higher diagnostic accuracy.


   ADVANCES IN KNOWLEDGE
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
IMPLICATION FOR PATIENT CARE
 References
 


   IMPLICATION FOR PATIENT CARE
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
 IMPLICATION FOR PATIENT CARE
References
 


   ACKNOWLEDGMENTS
 
We thank Yasuo Beppu, MD, Hirokazu Chuman, MD, Akira Kawai, MD, and Fumihiko Nakatani, MD, for assisting with clinical information.


   FOOTNOTES
 

Abbreviations: FDG = fluorine 18 fluorodeoxyglucose

Author contributions: Guarantors of integrity of entire study, all authors; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; manuscript final version approval, all authors; literature research, U.T., T.T., E.E.K.; clinical studies, all authors; statistical analysis, U.T., E.E.K.; and manuscript editing, U.T., E.E.K.

Authors stated no financial relationship to disclose.


   References
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
 IMPLICATION FOR PATIENT CARE
 References
 

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