About 20% of all human cancers are caused by chronic infection or chronic inflammatory states. Recently, a new hypothesis has been proposed for prostate carcinogenesis. It proposes that exposure to environmental factors such as infectious agents and dietary carcinogens, and hormonal imbalances lead to injury of the prostate and to the development of chronic inflammation and regenerative 'risk factor' lesions, referred to as proliferative inflammatory atrophy (PIA). By developing new experimental animal models coupled with classical epidemiological studies, genetic epidemiological studies and molecular pathological approaches, we should be able to determine whether prostate cancer is driven by inflammation, and if so, to develop new strategies to prevent the disease. NIH Public Access Author ManuscriptNat Rev Cancer. Author manuscript; available in PMC 2013 January 23. $watermark-text $watermark-text $watermark-textProstate cancer is the most common non-cutaneous malignant neoplasm in men in Western countries, responsible for the deaths of approximately 30,000 men per year in the United States 1 . The number of afflicted men is increasing rapidly as the population of males over the age of 50 grows worldwide. Therefore, finding strategies for the prevention of prostate cancer is a crucial medical challenge. As men in South East Asian countries have a low incidence of prostate cancer that increases rapidly after immigration to the West, this disease is not an intrinsic feature of ageing. The pathogenesis of prostate cancer reflects both hereditary and environmental components. What are the environmental factors and genetic variations that have produced such an epidemic of prostate cancer? Approximately 20% of all human cancers in adults result from chronic inflammatory states and/or chronic inflammation 2-4 (BOX 1), which are triggered by infectious agents or exposure to other environmental factors, or by a combination thereof. There is also emerging evidence that inflammation is crucial for the aetiology of prostate cancer. This evidence stems from epidemiological, histopathological and molecular pathological studies. The objective of this Review is to take a multidisciplinary approach to present and analyse such studies. Because several reviews related to these topics have been published [5][6][7] , here we will focus on new findings and ideas with the purpose of sparking innovative areas of investigation that might ultimately lead to the prevention of prostate cancer. Enigmas in the aetiology of prostate cancerAs in other cancers, prostate cancer develops through the accumulation of somatic genetic and epigenetic changes, resulting in the inactivation of tumour-suppressor genes and caretaker genes, and the activation of oncogenes 8,9 (TABLE 1). There is also evidence for an underlying genetic instability that might facilitate tumour progression 10,11 . Although these genetic and epigenetic changes are crucial for our understanding of 'how' prostate cancer arises, another key remaining question is 'why'...

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DNA double strand breaks (DSB) can lead to development of genomic rearrangements, which are hallmarks of cancer. TMPRSS2-ERG gene fusions in prostate cancer (PCa) are among the most common genomic rearrangements observed in human cancer. We show that androgen signaling promotes co-recruitment of androgen receptor (AR) and topoisomerase II beta (TOP2B) to sites of TMPRSS2-ERG genomic breakpoints, triggering recombinogenic TOP2B-mediated DSB. Furthermore, androgen stimulation resulted in de novo production of TMPRSS2-ERG fusion transcripts in a process requiring TOP2B and components of DSB repair machinery. Finally, unlike normal prostate epithelium, prostatic intraepithelial neoplasia (PIN) cells showed strong co-expression of AR and TOP2B. These findings implicate androgen-induced TOP2B-mediated DSB in generating TMPRSS2-ERG rearrangements.