MADRID, SPAIN (UroToday.com) - In this talk, Dr. Jochen Walz compared the modalities currently available for the imaging for bone metastases. He began with a discussion of the pathophysiology of bone metastasis. Circulating prostate cancer cells reach the bone marrow where shared adhesion molecules, like CXCR4, allow for tumor cell binding. Bone metastases are typically osteoblastic, osteosclerotic, or mixed, and only rarely osteolytic. Thus imaging of bone metastases typically demonstrates increased bone density and displacement of the bone marrow.
Currently the options available for imaging bone metastases in prostate cancer include bone scintigraphy (BS), x-ray, CT, MRI and PET. Dr. Walz reviewed the appearance of bone metastases on the various imaging modalities. Uptake of tracer in BS occurs at sites of bone formation due to the presence of high metabolic activity. He discussed that both x-ray and CT demonstrate evidence of bone resorption and osteogenesis—CT with higher resolution—and are typically used as confirmatory tests for BS. Changes on MRI occur early on, and are visible as displacement of the bone marrow, which appears as signal loss on T1, contrasting to the surrounding high-signal marrow fat. On PET, radioactive tracer is fixed at sites of bony lesions.
Dr. Walz then outlined the important characteristics to consider when deciding on an optimal imaging modality. These characteristics include diagnostic performance (i.e., sensitivity and specificity), availability, cost, and ability to quantify results. With regards to diagnostic performance, MRI detects 22-38% more lesions than BS and identifies 15-22% more patients with metastatic disease. With PET, Dr. Walz discussed that 18F-choline PET has been shown to identify 9% more patients with bony metastases than BS on initial staging, and 11C-choline PET has been shown to identify 15% more patients than BS in the setting of disease relapse. One pooled meta-analysis comparing MRI, PET, and bone scintigraphy demonstrated that MRI had the highest sensitivity at 95% compared to 87% and 79% for PET and BS, respectively. Specificity for MRI and PET were similar at 96% and 97%, respectively. BS specificity was shown to be 82% on pooled analysis. The pooled AUC for MRI, PET, and BS was 0.99, 0.95, and 0.89, respectively. Based on this data Dr. Walz stated that the diagnostic performance of MRI and PET are superior to BS.
With regards to availability, Dr. Walz pointed out that BS is more readily available in comparison to MRI and PET. In a comparison of costs, he noted that in France a whole body MRI costs 250€, a PET costs 1090€, and BS costs 170€. Whole body MRI takes the longest to perform at 50 minutes, while PET takes 25 minutes and BS 15 minutes. Thus, from a cost, availability, and resource utilization standpoint, BS is superior.
Dr. Walz noted that quantification is possible in all 3 techniques: with the bone scan index in BS, RECIST criteria with MRI, and SUV with PET. PET and MRI carry with them the advantage of providing more anatomic information then BS, allowing for the assessment of the lymph nodes and other abdominopelvic structures at the same time as the bone.
Based on all of this information, he concluded that each imaging modality has its advantages and disadvantages and the optimal tool is dependent on what the particular priorities are and what resources are available. MRI is the optimal tool at this time if diagnostic accuracy is the primary objective. If cost-effectiveness and availability are of primary concern, then BS provides reasonable diagnostic accuracy with a lower price tag.
Presented by Jochen C. Walz at the 30th Annual European Association of Urology (EAU) Congress - March 20 - 24, 2015 - IFEMA - Feria de Madrid - Madrid, Spain
Institut Paoli-Calmettes Cancer Centre, Marseille, France
Reported by Timothy Ito, MD, medical writer for UroToday.com