Prostate cancer is the most common solid organ cancer in men (1). The main objective of current non-invasive imaging techniques is to detect early-stage disease that is biologically aggressive in an attempt to offer timely curative treatments. The currently used screening and diagnostic tools include digital rectal examination; serum prostate-specific antigen (PSA) and non-targeted transrectal ultrasound (TRUS)–guided biopsy (3). Because of the limitations and poor specificity of the available diagnostic tools, significant efforts are being made into improving prostate cancer detection. It has been postulated that multiparametric MRI is useful in the detection and risk stratification of prostate cancer (4) and also, that MRI can serve as a real-time guide to adequately sample suspicious lesions in the prostate (5). Therefore, the objective of this study is to investigate magnetic resonance diffusion weighted imaging (DWI) quantification (or Apparent Diffusion Coefficient Quantification (ADC)) in suspicious prostate lesions as an imaging biomarker of malignancy, and to correlate the values with the results of MRI-guided prostate targeted sampling.IRB approved HIPAA compliant retrospective review of a 12-month period prospective cohort of patients presenting with persistently elevated or rising serum prostate specific antigen (PSA) and at least one lesion suspicious for prostate cancer that underwent MRI guided targeted biopsy. Diagnostic and interventional procedures were performed using a 32-element surface pelvic array coil on a 3T MAGNETOM Trio system (Siemens Medical Solutions, Erlangen, Germany). Single shot echo planar DWI was performed with tridimensional diffusion-encoding gradients utilizing b-values of 0, 1000, 1500 and 2000 s/mm² (TR = 6000 ms / TE = 89 ms / NSA = 7 / FOV = 300 mm / phase over sampling = 50% / slice thickness = 3 mm / BW = 1736 / base resolution = 160 / Ipat = 2 / TA = 7:20 min). Subsequent targeted biopsies of suspicious lesions were performed following transrectal placement of a Dyna-TRIM biopsy system (Invivo, Gainesville, FL). Pre-procedural imaging allowed identification of the transrectal fiducial line, target lesions, and tridimensional trajectory. Pathology results per lesion were correlated to pre-procedural ADC quantification. ADC was measured by placing a region of interest (ROI) in each lesion and in normal prostate tissue within the central and peripheral zones to assure consistency in each patient. Correlation between ADC values of tumors and anatomic pathology was evaluated with paired t-test. Receiver operating characteristic (ROC) curves were made to analyze ADC performance in discriminating low- and high-grade tumors (α=0.05).Thirty-five consecutive patients were recruited (mean age 63, range 55-82). Average PSA level was 9.3 ng/mL (median 7.76 ng/mL; SD 6.4 ng/mL). 179 suspicious lesions were successfully biopsied (Average number of lesions per patient 5, range 2-8) and all samples were deemed diagnostic. ADC values of the normal tissue in the central zone were significantly lower when compared to the peripheral gland (ADC value of the peripheral zone was 1,27 mm²/sec vs. ADC value of the central gland 0,97 mm²/sec, p<0.001). Overall cancer detection rate was 19/35 (54.2%). Pathology results were benign (inflammation) in 133 lesions (74.3%), and malignant in 43 lesions (24.7%), with low-grade cancer (Gleason score 6) in 12/179 (6.7%); and intermediate to high-grade cancer (Gleason score > 7) in 31/179 (17.3%). ADC values of intermediate and high-grade lesions (mean ADC = 0.685 mm²/sec, SD 0.109 mm²/sec) were significantly lower than low-grade lesions (mean ADC = 0.767 mm²/sec, SD 0.080 mm²/sec; p = 0.01). Also, all grades of prostate cancers demonstrated significantly restricted diffusion compared to benign lesions (mean ADC=0.877 mm²/sec, SD 0.162 mm²/sec; p <0.001). ROC curves are shown below (Figures 1 and 2). Figure 3 illustrates an example of a malignant lesion.Non-invasive quantitative ADC measurement is a reliable imaging biomarker for predicting malignancy and stratifying cancer risk in patients with persistently elevated or rising serum prostate specific antigen (PSA) levels and suspicious focal prostate abnormalities undergoing targeted tissue sampling under MRI guidance.