While transrectal ultrasound is widely used to guide prostate biopsy, traditional grayscale ultrasound is unreliable in prostate cancer diagnosis. However, there have been many newer approaches to ultrasound that have been introduced to improve both the sensitivity and specificity.
Contrast-enhanced ultrasound (CEUS), particularly when combined with contrast-ultrasound dispersion imaging (CUDI), can be used for prostate cancer diagnosis. Compared to systematic biopsy, MRI targeted biopsy and CUDI-targeted biopsy performed similarly with respect to the detection of clinically significant disease. However, the use of CUDI was associated with a lower positive predictive value, ie. more false-positive findings, due to benign prostatic hyperplasia (BPH) and prostatitis.
Instead of a single ultrasound modality, Dr. Mannaerts suggested the use of multiparametric MRI using a combination of greyscale to assess hypoechogenicity, CEUS for contrast enhancement, CUDI for microbubble kinetics, and shear wave (SWE) to assess tissue properties such as stiffness. The combined use of these approaches may allow for compensation of the limitations of each. Such an approach has been validated and shows improved diagnostic parameters compared to each component separately when using the surgical pathology gold standard.
Machine learning approaches may be used to integrate the multiparametric data.
Moving beyond modifications to existing ultrasound, Dr. Mannaerts discussed micro-ultrasound. Compared to traditional ultrasound which operated at 8 to 12 MHz, micro-ultrasound devices operated at 29 MHz which allows for much-improved resolution (up to 300% greater) allowing for better assessment of tissue abnormalities. Much like prostate imaging–reporting and data system (PI-RADS) for the interpretation of prostate MRI, a so-called prostate imaging–micro-ultrasound (PI-MUS) protocol provides a standardized approach to the interpretation of micro-ultrasound with a corresponding five-point scale associated with prostate cancer risk.
Preliminary data suggest the micro-ultrasound may diagnose some clinically significant prostate cancer which is missed by both systematic and MRI-targeted biopsy. In an early study, Dr. Robert Abouassaly and colleagues showed that micro-ultrasound changed the diagnosis in 8 of 38 patients with newly diagnosed prostate cancer. Further, unlike MRI in which scanning and biopsy are done at separate settings, micro-ultrasound allows real-time visualization and biopsy.
Previous data, including the PROMIS and PRECISION studies, have demonstrated the value of targeted biopsy, using MRI guidance. However, Dr. Mannaerts highlighted limitations of this pathway including cost and accessibility, inter-reader validity, registration issues, inter-operator variability, differences in expertise between operators and centers, and controversy regarding the need for concomitant systematic biopsy.
An optimized ultrasound-based approach offers the potential for reduced costs, improved accessibility, and improved lesion targeting. A comparative study would be particularly valuable to establish this new approach.
Presented by: Christophe Mannaerts, MD, Department of Urology, Amsterdam University Medical Center, Amsterdam, Netherlands
Written by: Christopher J.D. Wallis, MD, PhD, Urologic Oncology Fellow, Vanderbilt University Medical Center, Twitter: @WallisCJD at the Virtual 2020 EAU Annual Meeting #EAU20, July 17-19, 2020