Purpose. To examine the associations among intake of refined grains, whole grains and dietary fiber and aggressiveness of prostate cancer in African Americans (AA, ) and European Americans (EA, ) in a population-based, case-only study (The North Carolina-Louisiana Prostate Cancer Project, PCaP). Methods. Prostate cancer aggressiveness was categorized as high, intermediate or low based on Gleason grade, PSA level and clinical stage. Dietary intake was assessed utilizing the NCI Diet History Questionnaire. Logistic regression (comparing high to intermediate/low aggressive cancers) and polytomous regression with adjustment for potential confounders were used to determine odds of high prostate cancer aggressiveness with intake of refined grains, whole grains and dietary fiber from all sources. Results. An inverse association with aggressive prostate cancer was observed in the 2nd and 3rd tertiles of total fiber intake (OR = 0.70; 95% CI, 0.50–0.97 and OR = 0.61; 95% CI, 0.40–0.93, resp.) as compared to the lowest tertile of intake. In the race-stratified analyses, inverse associations were observed in the 3rd tertile of total fiber intake for EA (OR = 0.44; 95% CI, 0.23–0.87) and the 2nd tertile of intake for AA (OR = 0.57; 95% CI, 0.35–0.95). Conclusions. Dietary fiber intake was inversely associated with aggressive prostate cancer among both AA and EA men. 1. Introduction In the United States, prostate cancer currently is the most frequently diagnosed cancer in men and the second leading cause of cancer death in men after lung cancer [1, 2]. Clinically, prostate cancer is diagnosed as local (confined to the prostate), regional, or advanced (distant spread) [3]. Risk factors for prostate cancer may differ by disease aggressiveness. Therefore, determinants of mortality also might differ from those of incidence. Results from studies of various suspected risk factors for prostate cancer aggressiveness, such as body mass index ( ) and smoking, have been conflicting especially in the prostate-specific antigen (PSA) era (i.e., the past 20 years) [4]. Studies relying solely on incidence may have limited applicability to identifying risk factors for prostate cancer mortality because of the high survival rate of PSA-detected cancers [2]. African Americans (AAs) experience greater incidence and increased burden from late-stage diagnosis, aggressive tumor biology and much higher mortality compared to European Americans (EAs) [5, 6]. After adjusting for socioeconomic status, year and age at diagnosis, AA were found to be at increased risk of being diagnosed with
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