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Using MRI to Detect Bone Metastases in High-Risk Prostate Cancer Patients

MRI is more accurate than bone scans or plain radiographs for detecting bone metastases, but is better detection always the best course?

Evaluation of prostate cancer patients with suspected bone metastases has not changed in several decades. Technetium-99m bone scintigraphy (bone scans), with or without plain radiographs of equivocal areas, remains the standard of care for assessment. However, bone scans are inherently problematic, as this imaging modality has relatively poor specificity for identifying metastatic disease, and additional studies often are required to rule out metastases.

A group from Belgium performed a prospective evaluation of magnetic resonance imaging (MRI) of the axial skeleton as a single-step detection method versus multistep detection with bone scans plus follow-up modalities. They enrolled 66 asymptomatic high-risk patients with prostate cancer: 26 (39%) had locally advanced disease (Gleason score 8 and prostate-specific antigen [PSA] level 20), 12 (18%) had rising PSA levels less than 3 years after radical prostatectomy and PSA doubling times (DT) of less than 12 months, and 28 (42%) had PSA DT of less than 12 months in the castrate setting.

All patients underwent MRI and standard bone scans. After analysis of bone-scan results (and without knowledge of the MRI findings), clinicians requested supplemental plain radiographs and MRI images for 37 and 17 patients, respectively, to clarify results. In lieu of attempting bone biopsies for confirming metastases, the investigators used computed tomography (CT) correlation of the MRI findings and 6-month follow-up as the standard.

Forty-one patients (62%) were deemed to have metastatic disease by CT correlation and follow-up. MRI studies correctly identified metastatic disease in all 41 patients, including 7 whose bone scans and supplemental plain radiographs showed no evidence of metastases. In total, MRI identified 15 patients (23%) whose bone-scan and plain-radiograph results were considered negative or equivocal. Although 16 of 41 patients with metastases had lesions in areas not included in MRI evaluations, all of these patients also had involvement of the spine and pelvis, which was detected by MRI. This MRI strategy was cost-effective in Belgium (where costs for MRI are relatively low); however, MRI would not be cost-effective in the U.S. or France (where costs and reimbursement are higher).

Comment: Unquestionably, we need tests that are more specific for bone metastases in high-risk patients with prostate cancer; nevertheless, this issue is double edged. At autopsy, more than 90% of prostate cancer patients have bone metastases. Our current clinical practice with regard to providing local curative-intent therapies and systemic management has been developed around the less-than-perfect ability of bone scans and plain radiographs to detect bone metastases. For example, excluding high-risk patients from undergoing curative-intent local therapy simply because metastases are detected with imaging that is more sensitive and "specific" should be prospectively evaluated prior to widespread adoption. Ultimately, of course, the cost of MRI in the U.S. will hinder implementation of its use, even when we determine its proper role.

— Robert Dreicer, MD, MS, FACP

Published in Journal Watch Oncology and Hematology August 21, 2007

Citation(s):

Lecouvet FE 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 2007 Aug 1; 25:3281-7.

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