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Clinical Investigations |
1 Department of Medical Oncology, University Hospital Groningen, Groningen, The Netherlands
2 Department of Pathology and Laboratory Medicine, University Hospital Groningen, Groningen, The Netherlands
3 Department of Nuclear Medicine, University Hospital Groningen, Groningen, The Netherlands
4 Department of Radiology, University Hospital Groningen, Groningen, The Netherlands
| ABSTRACT |
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Key Words: carcinoid bone metastases imaging
| INTRODUCTION |
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(5,6) has changed the clinical presentation of carcinoid tumors. However, these agents failed to reduce the rate of tumor progression (3,7,8). As a result, symptoms related to tumor growth can prevail over metabolic symptoms. Consequently, a precise staging is of increasing importance for optimal management of carcinoid patients. The availability of partial liver resections and, in selected cases, liver transplantation (911) emphasizes the need for a thorough staging procedure (9). Despite the increasing need for precise staging, bone metastases may frequently remain undetected. This is suggested by the discrepancy observed between clinically detected bone metastases and postmortem findings. Bone metastases were clinically detected in 11 of 274 patients with advanced carcinoid tumors (4%) (95% confidence interval [CI], 2%6%) (12). In contrast to this relatively low rate, autopsy revealed a higher rate (42%) (95% CI, 26%58%) of bone metastases in 36 patients with advanced carcinoid tumors (13).
In noncarcinoid tumors the diagnosis of bone metastases is established by plain radiography, bone scintigraphy, and MRI (1416). Although markers of bone metabolism have a limited role in the diagnosis and follow-up of bone metastases, these markers may provide insight in their osteolytic or osteoblastic nature (1720). Octreotide scintigraphy is used as a sensitive first step in the staging of carcinoid tumors (21). However, the sensitivity of octreotide scintigraphy for bone metastases remains to be determined.
In this retrospective study we describe the clinical presentation of bone metastases in patients with carcinoid tumors. Furthermore, we compare the sensitivity of plain radiography, MRI, bone scintigraphy, and octreotide scintigraphy for the detection of bone metastases. Finally, we evaluate the osteolytic or osteoblastic nature of bone metastases using markers of bone metabolism.
| MATERIALS AND METHODS |
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Imaging Procedures
Plain skeletal radiography of sites with clinically suspected bone metastases was performed in 2 perpendicular directions according to standard procedures.
MRI was performed with a 1.0-T unit (Magnetom Impact; Siemens, Erlangen, Germany). Sites with suspected bone metastases were investigated with adjacent slices of 6- to 10-mm thickness, using the turbo inversion recovery modulus.
Whole-body bone scintigraphy was performed 34 h after intravenous injection of 600700 MBq 99mTc-methylenediphosphonate, using a large field-of-view double-head gamma camera (Multispect 2; Siemens Inc, Hoffman Estates, IL), together with a low-energy, high-resolution collimator.
For octreotide scintigraphy, planar images were acquired 24 h after intravenous administration of 200 MBq 111In-octreotide (Octreoscan; Mallinckrodt, Petten, The Netherlands). For acquisition, the same camera system as that used for bone scintigraphy was used, but with a medium-energy, all-purpose collimator. SPECT was performed when planar images were equivocal.
All imaging procedures were serially evaluated by investigators experienced in radiology or nuclear medicine. The sites of bone metastases were described in detail and the osteolytic or osteoblastic appearance on plain radiography was specified. An analysis was performed on a patient-by-patient basis to enable comparison between the respective imaging procedures. Because bone scintigraphy and octreotide scintigraphy both visualize the whole body, a lesion-by-lesion analysis could be used to compare the sensitivity of these techniques.
Markers of Serotonin Metabolism
Urinary 5-hydroxyindoleacetic acid (5-HIAA) concentration and platelet serotonin content were determined in a 24-h urine collection and in platelet-rich plasma by high-performance liquid chromatography with fluorometric detection. The reference interval for urinary 5-HIAA ranges from 0.8 to 3.8 mmol/mol creatinine. Platelet serotonin content, expressed as nanomoles per 109 platelets, was calculated by dividing the serotonin concentration in platelet-rich plasma by the concentration of platelets. The reference interval for platelet serotonin content ranges from 2.8 to 5.4 nmol per 109 platelets. A detailed description of the sampling procedures and analytic methods for urinary 5-HIAA and platelet serotonin has been published (23).
Markers of Bone Metabolism
In the patients with bone metastases, and in the control carcinoid patients without bone metastases, markers of bone metabolism were determined retrospectively in serum. The samples had been stored at -20°C until analysis. We preferred the measurement of recently developed, more specific markers (17,20) of bone metabolism. The serum bone-specific alkaline phosphatase (BSAP) activity and the amino-terminal propeptide of type I procollagen (PINP) concentration in serum were determined as markers of osteoblastic activity or bone formation. The serum concentration of the cross-linked amino-terminal telopeptide of type I collagen (NTx) was determined as a marker of osteoclastic activity or bone resorption. The serum BSAP activity was measured with the Metra-Biosystems immunoassay (Mountain View, CA). The BSAP assay has a reference range of 923 U/L and intra- and interassay coefficients of variance of 4.9% and 5.5%, respectively. The PINP concentration in serum was measured using a radioimmunoassay (Orion Diagnostica, Espoo, Finland). The reference range of the PINP assay is 2070 µg/L; the intra- and interassay coefficients of variance are 8.4% and 9.0%, respectively. The NTx serum concentration was measured using the Osteomark NTx Serum immunoassay (Ostex International, Seattle, WA). This NTx assay has a reference range of 524 nmol/L bone collagen equivalents per liter and has intra- and interassay coefficients of variance of 7.3% and 6.9%, respectively.
Statistics
Differences in the number of bone metastases in midgut versus foregut carcinoids were evaluated using
2 statistics. To compare the respective imaging modalities, we used the McNemar test together with the Fisher exact test.
To compare markers of bone metabolism between patients with bone metastases and the matched control patients, the Wilcoxon signed-rank test was used. Correlations between the respective markers of serotonin and bone metabolism were calculated with the Pearson correlation for markers with a normal distribution and the Spearman rank correlation for markers with a non-normal distribution. P < 0.05 was considered statistically significant.
| RESULTS |
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| DISCUSSION |
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A possible explanation for the high rate of bone metastases in the later studies could arise from the therapeutic use of somatostatin analogs and interferon-
. These agents relieve symptoms mediated by amines secreted by the tumor (1,3,6,27) but have only a limited effect on tumor growth (3,7). As a result, these agents can lead to a prolonged survival and a greater impact of symptoms related to tumor growth. In this situation, bone metastases, associated with advanced disease, may increasingly cause symptoms in carcinoid patients. An additional explanation for the high rate of bone metastases could be that the use of octreotide scintigraphy also reveals asymptomatic bone metastases, leading to a higher rate of bone metastases. However, only 1 of our patients had asymptomatic bone metastases detected by octreotide scintigraphy.
All of our patients with bone metastases had a carcinoid tumor from midgut origin. However, because of the small numbers of patients with bone metastases, we could not recognize a difference between midgut and foregut carcinoid patients. In contrast to our results, an earlier study (12) described a higher rate of bone metastases in 39 patients with foregut carcinoids (23%) (95% CI, 10%36%) than in patients with midgut carcinoids (1%) (95% CI, 0%2%). Accordingly, the patients with bone metastases described in several case reports (2830) had predominantly tumors from foregut origin.
Although our study is limited by its retrospective character, some clinical features deserve attention. All patients with bone metastases in our study had advanced disease, characterized by widespread metastases, elevated markers of serotonin metabolism, and the carcinoid syndrome. This could indicate that bone metastases occur in long-lasting disease.
The interval between diagnosis of a carcinoid tumor and the appearance of bone metastases shows a wide range within our patients. This is probably related to the indolent course of the disease and its difficult diagnosis. Although 2 patients had bone metastases at the time of diagnosis of the carcinoid tumor, all patients had bone metastases together with widespread extraosseous metastases (Table 2). Bone metastases were located predominantly in the axial skeleton; this distribution is comparable to that found in noncarcinoid tumors (31). Pain was the principal symptom in our patients. Bone metastases seem to follow a relatively uncomplicated course, which possibly results from the slow rate of growth that is characteristic of carcinoid tumors.
In our study the sensitivity for bone metastases ranged from 44% for plain radiography, 70% for octreotide scintigraphy, and 90% for bone scintigraphy to 100% for MRI. The small number of patients with bone metastases resulted in wide confidence intervals (Table 3). As a consequence, no significant differences between the sensitivity of the respective techniques were found. Only a limited number of previous studies address the imaging of bone metastases in patients with carcinoids and related neuroendocrine tumors. These studies describe small numbers of patients, comparable with our study. In a study of patients with gastrinoma (32), bone scintigraphy correctly diagnosed 5 of 8 patients with bone metastases. In their study, octreotide scintigraphy and MRI identified 6 and 7, respectively, of the 8 patients with bone metastases. The authors advocate the use of octreotide scintigraphy as a first step in the diagnosis of bone metastases. A second study (33), performed on patients with neuroendocrine tumors, compared octreotide scintigraphy with MRI. Octreotide scintigraphy showed bone metastases in 3 of 10 patients, whereas MRI identified all 10 patients with bone metastases. In another study (34) of 145 patients with gastroenteropancreatic neuroendocrine tumors, 19 (13%) were identified as having bone metastases. Octreotide scintigraphy showed bone metastases in all 19 patients, whereas bone scintigraphy showed bone metastases in 17 of 19 patients. Four of the 30 carcinoid patients included in this study (34) had bone metastases. In a recent study (35), octreotide scintigraphy showed bone lesions in 23 of 26 carcinoid patients with bone metastases (88%).
MRI appeared to be the most sensitive imaging technique in our study. This finding agrees with studies on noncarcinoid bone metastases (15,16,36,37). In these studies, MRI had a slightly higher sensitivity and specificity for bone metastases than bone scintigraphy. A disadvantage of MRI is that only a restricted part of the skeleton can be visualized in 1 investigation. Both bone scintigraphy and octreotide scintigraphy have the advantage of imaging the whole body.
Octreotide scintigraphy has a prominent role in the detection of tumor deposits in carcinoid tumors (21). However, our results suggest that the sensitivity for bone metastases is higher for bone scintigraphy than for octreotide scintigraphy. Bone scintigraphy identified more patients with bone metastases than octreotide scintigraphy. Furthermore, the number of lesions visualized with bone scintigraphy was higher than that with octreotide scintigraphy. Nevertheless, both scintigraphic procedures showed bone lesions not detected by the other scintigraphic techniques (Table 4; Fig. 2). Therefore, bone scintigraphy and octreotide scintigraphy can provide complementary information about the presence of bone metastases. The combination of bone scintigraphy and octreotide scintigraphy identified all patients with bone metastases in our study. Probably, there are 2 factors determining whether a bone lesion can be visualized by 1 or both scintigraphic procedures. Visualization by bone scintigraphy identifies those metastases that induce an osteoblastic reaction. On the other hand, visualization by octreotide scintigraphy requires the presence of octreotide receptors. The complementary imaging of bone metastases suggests that bone metastases can show different imaging characteristics in 1 patient.
To our knowledge, the role of markers of bone metabolism in carcinoid patients has not been investigated previously. In our study, the measurement of BSAP, PINP, and NTx did not distinguish patients with bone metastases. Furthermore, formation markers were not preferentially elevated compared with resorption markers (Fig. 3) and, therefore, failed to reflect the predominantly osteoblastic appearance that is described for bone metastases from carcinoid tumors (28,29). The low sensitivity of the markers of bone metabolism is possibly explained by one of the following mechanisms. Because carcinoids are slowly growing tumors, bone metastases may have only limited impact on the metabolism of the surrounding normal bone. These minor changes in bone metabolism are not easily detected. Furthermore, somatostatin analogs inhibit the pituitary secretion of growth hormone, resulting in low levels of insulin-like growth factor I (38). This inhibition possibly affects bone metabolism and can, therefore, influence markers of bone metabolism. Finally, serotonin exerts a stimulating effect on collagen formation, mediated by transforming growth factor-ß (39,40). Because carcinoids produce excessive amounts of serotonin, a stimulated collagen formation may obscure small changes in bone collagen metabolism. Possibly because of these interfering mechanisms, markers of bone metabolism are not sensitive enough to detect the predominantly osteolytic or osteoblastic behavior of bone metastases.
| CONCLUSION |
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| FOOTNOTES |
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For correspondence or reprints contact: Elisabeth G.E. de Vries, MD, PhD, Department of Medical Oncology, University Hospital Groningen, P.O. Box 30.001, 9700 RB Groningen, The Netherlands.
E-mail: e.g.e.de.vries{at}int.azg.nl
| REFERENCES |
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