Contrast-enhanced US not quite ready to replace prostate biopsy

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Contrast-enhanced ultrasound (US) may be used as a diagnostic tool in patients with suspected prostate cancer, but it cannot provide complete biopsy guidance or replace biopsy, according to a meta-analysis published in the February issue of Academic Radiology.

Current methods to diagnosis prostate cancer remain less than optimal. The disease is multifocal and heterogeneous, which makes it challenging to identify all cancer, sites and grades, according to Yanmi Li, MD, from the Chinese People’s Liberation Army General Hospital in Beijing, and colleagues. The reference standard, transrectal ultrasound-guided systematic biopsy, can miss clinically relevant cancers.

“The development of contrast agents and CEUS [contrast-enhanced ultrasound] techniques might improve both the visualization of tumor vascularity and the delineation of tumors,” wrote Li and colleagues.

The researchers devised a meta-analysis to determine the accuracy of contrast-enhanced ultrasound in the diagnosis of prostate cancer. They searched the MEDLINE, EMBASE and Cochrane Library databases for studies published up to August 2012. The meta-analysis included 16 studies with 2,624 patients.

Pooled diagnostic performance for the 16 studies estimated sensitivity of 0.70, specificity of 0.74, positive-predictive value of 0.59, negative-predictive value of 0.82, positive likelihood ratio of 2.81, negative likelihood ratio of 0.35 and diagnostic odds ratio of 9.09.

Li and colleagues observed heterogeneity between individual study results, which may be attributed to random variation between studies, variation of study characteristics and variation in the diagnostic threshold required for a positive result.

They acknowledged limitations to the meta-analysis, including the use of prostate needle biopsy cores, which is not an ideal gold standard, as the reference method for many studies. In addition, several studies were limited to the peripheral zone.

Accuracy of CEUS depends on diagnostic criteria and operator training and expertise, according to Li et al. They called for standardization of imaging techniques, contrast agents and diagnostic criteria as well as large samples, multicenter studies and high-quality prospective trials.