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Journal of Clinical Oncology, Vol 25, No 36 (December 20), 2007: pp. 5837-5838 © 2007 American Society of Clinical Oncology. DOI: 10.1200/JCO.2007.14.3875
MRI or Bone Scan or Both for Staging of Prostate Cancer?Division of Clinical Oncology, Royal Marsden Hospital, Sutton, Surrey, United Kingdom
Division of Radiology, Royal Marsden Hospital, Sutton, Surrey, United Kingdom
Division of Nuclear Medicine, Royal Marsden Hospital, Sutton, Surrey, United Kingdom To the Editor: We read with interest the article entitled "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 and are intrigued by the excellent results reported with magnetic resonance imaging (MRI) over bone scan. We would like to comment on the criteria used in the study to categorize abnormal uptake on radionuclide bone scan as either malignant or equivocal, which might have biased the results of the study. The benefit of bone scan for staging prostate cancer is that it detects metastasis before it is evident on plain radiographs. Conventional wisdom suggests that if the radionuclide bone scan shows uptake that is not explained by a benign lesion on targeted radiographs (TXR), the inference is that it is most likely to represent a malignant process, rather than equivocal, as has been categorized by the authors.2,3 Additional confirmation with other imaging including MRI may not be required in such instances in routine clinical practice. We beg to differ when the authors state that the abnormal uptake on the bone scan demonstrated in Figure 1 of the article1 is equivocal. In fact, it is highly suggestive of skeletal metastasis, given that there is no benign lesion or abnormality in the TXR to account for the increased uptake on bone scan, and this patient does not necessarily require an MRI to clarify the bone lesion as being malignant. Alternately, if there was a benign radiographic explanation for the bone scan uptake, then again the patient may not require an MRI for clarification. The bias in the reporting of bone scans in the study is shown when the authors state that "MRIa had no false-negative results." Abnormal uptake on bone scan may be due to a malignant process, even though it did not showing up as malignant on other imaging (TXR or axial MRI). In these circumstances, bone scans in this study seem to have been classified as equivocal, although they are positive, hence the resulting false-negative MRI may have been missed. Furthermore, when the authors state that "none of the patients without axial metastasis (on MRIa) had metastasis elsewhere," has the abnormal uptake on bone scan due to metastasis outside the axial skeleton been categorized as not malignant when it did not show up on TXR? This under-reporting of malignant lesions may have contributed to the low sensitivity (46%) and specificity (32%) attributed to bone scan in the study. The inclusion criteria of the study also may have biased the results, given that 28 of the 66 patients were already receiving hormonal treatment. In such instances the uptake of radionuclide on bone scan may be diminished because of the response to androgen deprivation. The utility of investigations differs depending on whether they are performed for initial staging before systemic treatment or for imaging while receiving treatment. The benefit of MRI may be for patients who are already receiving systemic treatment, whereas a bone scan without a baseline comparator has its drawbacks. In the 38 patients with newly diagnosed disease in the study, MRI identified metastasis in three of the 14 patients with normal bone scan/TXR findings and in two of the 12 patients with equivocal bone scan/TXR findings, which were confirmed with investigations and clinical information after 6 months of follow-up. Six months may not be an adequate period of follow-up to determine whether the equivocal bone scan findings may in fact represent metastasis, especially because these patients may have received systemic treatment during this period. The results of this study may be misleading because they erroneously suggest that MRI, although a more sensitive investigation, could replace bone scan as the initial and sole imaging modality of choice. However, we believe that bone scan, although not perfect, still remains the imaging investigation of choice for the initial staging of prostate cancer patients, with TXR correlation and other imaging including MRI to be used when results are truly equivocal. Bone scan and MRI may be considered as complementary imaging modalities in this clinical setting. 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. Jacobson AF, Stomper PC, Cronin EB, et al: Bone scans with one or two new abnormalities in cancer patients with no known metastases: Reliability of interpretation of initial correlative radiographs. Radiology 174:503-507, 1990 3. Citrin DL, Hougen C, Zweibel W, et al: The use of serial bone scans in assessing response of bone metastases to systemic treatment. Cancer 47:680-685, 1981[CrossRef][Medline]
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Copyright © 2007 by the American Society of Clinical Oncology, Online ISSN: 1527-7755. Print ISSN: 0732-183X
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