Purpose. To determine association between apparent diffusion coefficient value on diffusion-weighted imaging and Gleason score in patients with prostate cancer. Methods. This retrospective case series was conducted at Radiology Department of Aga Khan University between June 2009 and June 2011. 28 patients with biopsy-proven prostate cancer were included who underwent ultrasound guided sextant prostate biopsy and MRI. MRI images were analyzed on diagnostic console and regions of interest were drawn. Data were entered and analyzed on SPSS 20.0. ADC values were compared with Gleason score using one-way ANOVA test. Results. In 28 patients, 168 quadrants were biopsied and 106 quadrants were positive for malignancy. 89 lesions with proven malignancy showed diffusion restriction. The mean ADC value for disease with a Gleason score of 6 was 935？mm2/s ( ？mm2/s); Gleason score of 7 was 837？mm2/s ( ？mm2/s); Gleason score of 8 was 614？mm2/s ( ？mm2/s); and Gleason score of 9 was 571？mm2/s ( ？mm2/s). Inverse relationship was observed between Gleason score and mean ADC values. Conclusion. DWI and specifically quantitative ADC values may help differentiate between low-risk (Gleason score, 6), intermediate-risk (Gleason score, 7), and high-risk (Gleason score 8 and 9) prostate cancers, indirectly determining the aggressiveness of the disease. 1. Introduction Carcinoma of the prostate is a significant health issue affecting predominantly elderly men. In the year 2012 in United States of America (USA), estimated new cases and deaths from prostate cancer are 241,740 and 28,170 respectively [1]. Worldwide prostate cancer ranks third in cancer incidence and sixth in cancer mortality. The incidence of prostate cancer is not high in Pakistan, with an estimated figure of 3/100,000 of population. The possible explanation for this is lower life expectancy and no established screening programme for prostate cancer in Pakistan [2]. The diagnosis of prostate cancer is based on a digital rectal examination (DRE) and assessment of serum prostate specific antigen (PSA) followed by transrectal ultrasound (TRUS)-guided biopsy. Magnetic resonance imaging (MRI) of prostate cancer with conventional T2-weighted imaging is routinely used for diagnosis and local staging of prostate cancer along with biopsy. The presence of extra capsular extension and seminal vesicle invasion are sought. However, the more recent application of functional MRI, including diffusion-weighted imaging (DWI), MR spectroscopy, and dynamic contrast enhanced MR, has strong potential to expand the role of MRI by
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