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Journal of Clinical Oncology, Vol 26, No 7 (March 1), 2008: pp. 1189-1190 © 2008 American Society of Clinical Oncology. DOI: 10.1200/JCO.2007.15.3833
Magnetic Resonance Imaging Versus Bone Scan in High-Risk Prostatic Carcinoma: Some Methodological ConsiderationsDepartment of Nuclear Medicine, KCL Medical Center, Leeuwarden, the Netherlands
Department of Nuclear Medicine, Saint-John's General Hospital, Brugge, Belgium To the Editor: We read with interest the article "Magnetic resonance imaging of the axial skeleton for detecting bone metastases in patients with high-risk prostate cancer: Diagnostic and cost-effectiveness and comparison with current detection strategies" by Lecouvet et al.1 The authors compare a sequential work-up consisting of bone scanning, complemented, if necessary, with x-rays and with magnetic resonance imaging (MRI), with a one-step MRI of the axial skeleton to detect bone metastases in patients with high-risk prostate cancer. They find one-step MRI to be more sensitive than the sequential work-up. However, we feel that several aspects of their study deserve some comment. First, it is unfortunate that bone scanning was limited to anterior and posterior planar images and did not include single-photon emission computed tomography (SPECT). It has been demonstrated beyond any doubt that tomographic imaging enhances both sensitivity and specificity for the detection of bone metastases, both in cancer patients in general2,3 and in prostatic cancer patients in particular.4 The added benefit of tomographic imaging far outweighs the extra time needed at no further radiation dose and only slight added cost. Several vendors of scintigraphic cameras now offer the possibility of whole-body SPECT, which may substitute for whole-body planar imaging. This makes it all the more unfortunate that Lecouvet et al have not included SPECT, the optimal state-of-the-art technique, in the methodology used. Second, the statistical analysis that the authors performed is unusual. They always considered equivocal findings as wrong: in patients with metastases, these were interpreted as benign lesions; in patients without metastases, these were interpreted as metastases. The authors concede that this may have lowered the sensitivity and specificity that they calculated. But, more than that, this approach does not at all reflect clinical practice. Faced with an equivocal result, one may invoke another technique to try and relieve the uncertainty. Otherwise, one could either count all equivocal findings as metastases, or all as benign. Since it is not known beforehand which patients harbor metastases and which do not, it is not conceivable that equivocal lesions would be assigned to the metastases group in patients without metastases, and vice versa, as the authors have done in their statistical analysis. Therefore, a far more realistic statistical analysis would take into account two possibilities, one in which all equivocal lesions would be considered as metastases, and another in which all these would be considered as benign. In the first case, the sensitivity would be high at the cost of the specificity, and in the second case, the reverse would be true. In fact, this would constitute a simple ROC analysis, the results of which would far better reflect clinical use than does the analysis provided by the authors. Third, when x-rays did not show either a benign or a malignant explanation to equivocal bone scan findings, these results were classified by the authors as equivocal or discrepant. In clinical practice, a normal bone radiograph associated with an abnormal scan is highly suggestive of malignant disease, as exemplified by the case presented by the authors in their Figure 1.5 In conclusion, both the failure to perform SPECT, which may help to reduce the number of equivocal findings, and the inappropriate statistical treatment of equivocal results, may have distorted the conclusions from Lecouvet's study. AUTHORS’ DISCLOSURES OF POTENTIAL CONFLICTS OF INTEREST The author(s) indicated no potential conflicts of interest. REFERENCES
1. Lecouvet FE, Geukens D, Stainier A, et al: Magnetic resonance imaging of the axial skeleton for detecting bone metastases in patients with high-risk prostate cancer: Diagnostic and cost-effectiveness and comparison with current detection strategies. J Clin Oncol 25:3281-3287, 2007 2. Han LJ, Au-Yong TK, Tong WC, et al: Comparison of bone single-photon emission tomography and planar imaging in the detection of vertebral metastases in patients with back pain. Eur J Nucl Med 25:635-638, 1998[CrossRef][Medline] 3. Schirrmeister H, Glatting G, Hetzel J, et al: Prospective evaluation of the clinical value of planar bone scans, SPECT, and (18)F-labeled NaF PET in newly diagnosed lung cancer. J Nucl Med 42:1800-1804, 2001 4. Even-Sapir E, Metser U, Mishani E, et al: The detection of bone metastases in patients with high-risk prostate cancer: 99mTc-MDP Planar bone scintigraphy, single- and multi-field-of-view SPECT, 18F-fluoride PET, and 18F-fluoride PET/CT. J Nucl Med 47:287-297, 2006 5. McKillop J, McDougall IR: The role of skeletal scanning in clinical oncology. BMJ 281:407-410, 1980
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Copyright © 2008 by the American Society of Clinical Oncology, Online ISSN: 1527-7755. Print ISSN: 0732-183X
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