Prostate cancer imaging: what the next decade holds

Abstract

Prostate carcinoma is the most commonly diagnosed malignancy and the second most common cause of male cancer death in the USA [1]. Autopsy and early observational studies have shown that approximately one out of three men above the age of 50 years has histologic evidence of prostate carcinoma. While a portion of these tumors may be very aggressive and lethal, others are possibly clinically insignificant [2]. Identifying the lethal form of this tumor remains a challenge in this heterogeneous malignancy. The clinical presentation of prostate cancer may range from an asymptomatic condition to a rapidly progressive systemic illness. Prostate specific antigen (PSA) screening has resulted in earlier detection and a downstaging of prostate cancer at diagnosis. At the same time, the commonly used PSA cutoff of 2.5 ng/ml, used by urologists for biopsy, also leads to a significant number of unnecessary biopsies, leading to over diagnosis and overtreatment of indolent disease [3]. Thus far, imaging has only played a relatively small role in the management of localized prostate cancer. The current standard imaging techniques, such as transrectal ultrasound (TRUS), MRI, computed tomography (CT) and nuclear medicine studies, are not able to detect early disease, and only provide limited information for tumor, node, metastasis staging [4]. However, the role of imaging in patients with prostate cancer is evolving. New techniques are under investigation, either alone or combined with standard imaging techniques. TRUS is usually used to guide biopsies and to place brachytherapy seeds, but it does not reliably differentiate healthy from malignant prostate gland tissue. Contrast-enhanced color Doppler imaging, intermittent harmonic imaging and contrast-enhanced flash-replenishment imaging are now combined with standard TRUS. Contrast-enhanced ultrasound takes advantage of an increased density of micro vasculature in cancerous tissue compared with benign prostate tissue. Using micro bubble contrast agents, which diffuse into microvessels, this technique selectively enhances areas with increased vascularity. However, because of the relatively large size of microbubbles (~5–10 μm), leakage into the tumor cannot be well visualized and enhancement can also be due to benign conditions, such as prostatitis [5]. In a recent study of 114 patients with elevated PSA levels and previous negative biopsy contrast-enhanced advanced dynamic flow, Tina Islam