Keywords

Introduction

Prostate cancer is a leading cause of morbidity and mortality among men in the United States and Western Europe [1]. Widespread screening with prostate-specific antigen (PSA) and early treatment of localized prostate cancer have contributed to a decrease in age-adjusted rates of death due to prostate cancer [2]. Advancing age, diet, lifestyle-related factors, family history and ethnicity have long been recognized as contributors to the risk of prostate cancer [3]. Recent discoveries in the genetics of prostate cancer and in the acquired mutations that accumulate in prostate cancer cells have improved our understanding of the development of prostate cancer [1]. Evidence supporting the role of genetic factors comes from studies of relatives of patients with prostate cancer, founder populations, genome-wide association studies (GWAS), case-control studies and linkage analyses and from studies in patients with abnormalities in known cancer syndrome-associated genes such as BRCA1 and BRCA2 [4].

Hereditary Prostate Cancer

The risk of prostate cancer is increased approximately twofold in men with affected first-degree relatives [5]. This risk is increased further if more than one family member is affected or if there is early age of onset in a family member [6, 7]. In a cohort study of 44,000 pairs of Scandinavian twins, concordance for cancer in identical twins was higher for prostate cancer than either breast or colorectal cancer [8]. This study estimated that as much as 42% of the risk of prostate cancer could be explained by heritable factors. Interestingly, in addition to increasing the risk of developing prostate cancer, genetic factors may also influence the prognosis in these men. In a Swedish study in men with prostate cancer whose fathers also had prostate cancer, the survival of sons was similar to that of their fathers [9].

As with other cancers, familial clustering of prostate cancer has been reported. The Massachusetts Male Aging Study of 1149 Boston-area men found a much higher risk for prostate cancer among men with a family history of the disease which appeared to be independent of environmental factors [10]. Further associations between family history and risk of prostate cancer were characterized in a population-based case-control study of 1557 men aged 40–86 years [11]. At baseline, 4.6% of the cohort reported a family history of prostate cancer in a brother or father, and this was positively associated with prostate cancer risk after adjustment for age, alcohol and dietary factors. However, at least some of this familial clustering is due to increased prostate cancer screening in families thought to be at high risk [12].

This recognition that prostate cancer clusters within families has led investigators to collect multiple-case families in order to localize prostate cancer susceptibility genes through linkage analysis. It is now estimated that 5–10% of prostate cancer cases are primarily caused by high-risk inherited genetic factors or prostate cancer susceptibility genes [13,14,15]. Linkage analysis studies have mapped several susceptibility loci, and a number of genes have been cloned at these loci [5]. These include 1q24–25 (HPC1/RNASEL), 1q42.2–43 (PCAP), Xq27-q28 (HPCX), 1p36 (CAPB), 20q13 (HPC20), 8p22–23 (MSR1), 8q24 and 17p11 (HPC2/ELAC2) [16,17,18,19,20,21,22,23,24,25,26] (see Table 5.1). However, the replication of these findings remains inconsistent, with numerous genes likely to be involved in prostate cancer.

Table 5.1 Susceptibility genes and their loci identified in linkage analyses

Ethnic groups and founder populations are of particular interest for genetic mapping of complex traits due to a lack of genetic heterogeneity. African-American men have the world’s highest incidence of prostate cancer and a twofold higher mortality rate compared to Caucasians [27]. Admixture mapping has identified a number of chromosomal regions associated with prostate cancer in African Americans including the inherited variation at the 8q24 risk locus which appears to contribute to differences in African-American and European-American incidence of the disease [28,29,30]. Ashkenazi Jewish men have a higher incidence of mutations in BRCA1 and BRCA2 genes than the general population, and studies have reported a significant increased risk of prostate cancer in these men [31].

Although linkage studies have provided evidence that prostate cancer has a strong genetic component, identifying specific genes that contribute to the development of the disease has proven more difficult. Using gene sequencing technology, it has been possible to identify rare genes associated with an increased cancer risk [32]. Susceptibility genes with an associated increased risk for prostate cancer that have been identified include ZNF652, PRAC, EMSY, KLF6, AMACR, NBS1, SRD5A2, ER-beta, E-cadherin (CDH1), CHEK2, BRCA1 and BRCA2 [33,34,35,36,37,38,39,40,41,42,43,44,45,46] (see Table 5.2).

Table 5.2 Susceptibility loci identified with genome-wide association studies

Single nucleotide polymorphisms (SNPs) can be used to identify candidate genes by identifying alleles that are associated with an increased susceptibility to prostate cancer [47]. Using GWAS that include SNPs, more than 100 prostate cancer susceptibility loci have been identified, explaining an estimated 30% of the familial risk for this disease [48]. Based on combined risks conferred by known risk loci, the top 1% of the risk distribution has a 4.7-fold higher risk than the average of the population [49]. Among the genes that have been identified in this way are HOXB13, MSMB, LMTK2, KLK3, CPNE3, IL16, CDH13, and HNF1B [49,50,51,52,53].

BRCA1 and BRCA2 Genes

The BRCA1 and BRCA2 genes are tumour suppressor genes inherited in an autosomal dominant pattern with reduced penetrance [54, 55]. The development of cancer in individuals with germline mutations in the BRCA genes requires somatic mutation of the remaining wild-type allele [56]. The BRCA1 and BRCA2 genes encode proteins that maintain genomic stability by promoting repair of DNA double-strand breaks [57]. The main functions of BRCA1 are DNA damage response and repair, transcriptional regulation and chromatin modelling [58, 59]. The role of BRCA2 is more limited to DNA repair by homologous recombination including regulating RAD51 activity, an important component of the DNA repair process [60]. Therefore, functional loss of BRCA1 or BRCA2 leads to a deficiency in repairing DNA double-strand breaks by conservative mechanisms, allowing cells to repair these lesions through other methods which are potentially mutagenic. This genomic instability may explain the increased risk of cancer caused by deleted mutations in the BRCA genes, although it is unclear why these mutations are particularly associated with certain cancers such as breast and ovarian cancer and, less commonly, prostate cancer [61].

BRCA Genes and Cancer Risk

Germline mutations in the BRCA genes have been shown to be associated with an increased risk of breast and ovarian cancer [33, 62]. The extent to which BRCA mutation carriers are at an increased risk of other cancers has been less clear; however, the presence of BRCA1 or BRCA2 mutations in men has been shown to be associated with an increased risk of developing prostate cancer [31, 43, 63,64,65,66,67,68,69,70]. As an example, in a cohort study that involved 3728 men from 173 breast–ovarian cancer families with BRCA2 mutations, the estimated relative risk (RR) of prostate cancer among BRCA2 carriers was 4.7-fold greater than controls [71] (see Table 5.3). The risk of developing prostate cancer in BRCA1 mutation carriers appears to be lower (see Table 5.4). In a multinational cohort study of 11,847 individuals with BRCA1 mutations, the risk of prostate cancer was elevated 1.8-fold in men under the age of 65, but this increase was not observed in older men [73].

Table 5.3 Case-control studies and case series in men with BRCA2 mutation
Table 5.4 Case-control studies and case series in men with BRCA1 mutation

Prostate cancer in men with BRCA2 mutations also appears to be associated with more aggressive histology and a substantially worse prognosis [63, 74,75,76]. In a study from Iceland that included 30 men with a mutation in BRCA2, prostate cancer was diagnosed at an earlier age (69 versus 74 years) and was associated with a significantly shorter survival (2.1 versus 12.4 years) [77]. Similarly, in a multinational cohort study of men with prostate cancer that included 183 men from known BRCA2 families and 119 from BRCA1 families, those from BRCA2 families had a significantly shorter survival (4.0 versus 8.0 years) [78]. A Spanish study of 2,000 men with prostate cancer confirmed the worse prognosis in mutated BRCA2 patients with a significant survival advantage if patients were noncarriers (15.7 versus 8.6 years) [76].

The IMPACT trial (Identification of Men with a genetic predisposition to ProstAte Cancer: Targeted screening) is looking at the feasibility and role of PSA screening in men who are carriers for BRCA1 or BRCA2 mutations [79]. Results from the initial screening round in this study showed a detection rate for prostate cancer of 2.4%. There was an evidence of a more aggressive phenotype in these patients with more than two-thirds of the prostate cancer detected in the BRCA2 carriers being classified as intermediate or high risk. Furthermore, the only cancers detected in men younger than 50 years of age were in BRCA1 and BRCA2 carriers. A study by Castro et al. showed that BRCA carriers treated for localized prostate cancer have worse outcomes than noncarriers because they relapse and progress earlier to lethal metastatic disease [75]. This data adds to the increasing evidence that BRCA1 and BRCA2 mutation carriers develop more aggressive disease at a younger age suggesting that screening may be beneficial in this subgroup [79].

BRCA and Tumourigenesis

It has been proposed that the BRCA genes may act as tumour suppressors in prostate cells and that their functional loss predisposes to the development of premalignant prostatic lesions [80, 81]. It has been shown in animal studies that the simultaneous deletion of BRCA2 and the tumour suppressor p53 give rise to focal hyperplasia and high-grade PIN [80]. Furthermore, evidence has shown that functional BRCA1 and BRCA2 proteins may limit the metastatic potential of neoplastic cells [81]. This is achieved by downregulating MMP-9 production through inhibition of PI3-kinase/AKT and activation of MAPK/ERK pathways, which prevents cancer cell migration and invasion [82, 83].

Poly(ADP-ribose) Polymerase 1 (PARP1)

The DNA repair defect associated with mutations in BRCA1 or BRCA2 is being used to develop new targeted therapeutic approaches for prostate cancer [84, 85]. Poly(ADP-ribose) polymerase 1 (PARP1) is a nuclear enzyme which assists in the maintenance of genomic stability by identifying sites of DNA damage and recruiting repair mechanisms [86]. A number of studies indicate that tumour cells with a defect in homologous recombination, such as tumours bearing BRCA1 or BRCA2 mutations, depend on compensatory DNA repair of double-strand breaks, for which the enzyme PARP1 is essential [87, 88]. Consequently, tumours with defects in homologous recombination are hypersensitive to drugs that inhibit PARP [89]. PARP has also been implicated in the transcription regulation of the androgen receptor (AR) and has also shown antitumor activity in preclinical models of TMPRSS2-ERG-rearranged prostate cancer [90]. Additionally, PARP inhibitors suppress AR-target gene expression and tumour proliferation [91]. This had led to several studies examining the role of PARP inhibitors in prostate cancer [92,93,94]. Olaparib is a PARP inhibitor which has shown antitumor activity in both germline and sporadic cases of metastatic, castration-resistant prostate cancer with DNA-repair defects [93].

Susceptibility Genes

Androgen Receptor (AR) Gene

The androgen pathway and its function in the development and progression of prostate cancer has been well established, and overexpression of the AR gene has been associated with poor prognosis [95]. Altered activity of the androgen receptor caused by inherited variants of the AR gene, located on the X chromosome, may increase the risk of prostate cancer [96]. The length of the polymorphic trinucleotide CAG and GGN microsatellite repeats in exon 1 of the AR gene has been associated with an increased risk of prostate cancer; however, data from other studies has been conflicting [97, 98]. Germline mutations in the AR gene associated with an increased risk of prostate cancer have been identified. In a Finnish study, the R726L substitution in the AR gene may confer up to sixfold increased risk of prostate cancer and may contribute to cancer development in up to 2% of prostate cancer patients [99]; however, a subsequent Finnish study did not replicate these results [100]. Therefore, germline AR mutations may only contribute to a small fraction of familial and early-onset cases of prostate cancer.

RNASEL Gene

The RNASEL gene (encodes for RNase L enzyme) has been mapped to the HPC1 (hereditary prostate cancer 1) region at 1q24–25 and regulates cell proliferation and apoptosis through the interferon-regulated 2–5A pathway [101, 102]. Interestingly, much of the evidence for a role for RNASEL in prostate cancer seems to be in cases with a positive family history, supporting the initial discovery in hereditary patients [103]. Multiple variants of the RNASEL gene have been described including Arg462G, 471delAAAG, R462Q, E265X and D541E and may be involved in up to 13% of prostate cancer cases, though the true role of RNASEL genetic variation and its influence on prostate cancer risk have been controversial [104, 105]. The R462Q variant was originally associated with an increasing risk of prostate cancer due to a significant decrease in RNASE L enzymatic activity; however, this finding has not been universally replicable [104, 106, 107]. Furthermore, results of a meta-analysis of ten independent RNASEL genotyping studies for the variants E265X, R462Q and D541E suggested that although there was no overall effect on prostate cancer risk, there was a less than twofold increase in the risk of developing prostate cancer in Caucasians with the D541E variant [108]. Missense mutations in R462Q and D541E have been shown to be associated with an increased risk of advanced-stage disease only in the pre-PSA era with no effect on survival [109].

TMPRSS2-ERG Gene Fusion

Fusions of the androgen-regulated gene TMPRSS2 to the oncogenic ETS transcription factor ERG occur in over 50% of prostate cancers [110]. It has been found to vary according to ethnic groups, to be associated with p53 mutation expression and to have a more aggressive phenotype [111, 112]. Significant association of TMPRSS2-ERG fusion-positive prostate cancer with rare variants in the DNA repair genes POLI (variant F532S) and ESC01 (variant N191S) has also been found [113]. Furthermore, linkage analysis has found the presence of an inherited susceptibility to develop the TMPRSS2-ERG fusion with several loci located on chromosomes #9, #18 and X [114, 115]. Therefore, familial aggregation of TMPRSS2-ERG could be due to an inherited chromosomal instability caused by variations in the DNA repair pathway leading to genomic instability. ERG has been also shown to interact with the PARP1 enzymes in the DNA repair pathway, and interestingly PARP1 inhibitors have been shown to inhibit ERG-positive prostate cancer xenograft growth in a manner similar to that of BRCA1/2 deficiency [90].

HOXB13

The homeobox B13 (HOXB13) gene codes for a transcription factor that is important in prostate development [116,117,118]. Linkage to 17q21–22 was initially reported by the Prostate Cancer Genetics Project at the University of Michigan from pedigrees of families with hereditary prostate cancer [119, 120]. Next-generation sequencing of the 17q21–22 region identified the G84E variant of the HOXB13 gene in families with hereditary prostate cancer [116, 121]. Researchers have demonstrated that the HOXB13 G84E mutation is present in about 5% of prostate cancer families, predominantly of European descent, and have shown it to be associated with an increased prostate cancer risk [122] (see Table 5.5). In Europe, the prevalence of the HOXB13 G84E is highest in the Nordic countries, especially Finland and Sweden with a prevalence among men diagnosed with familial prostate cancer of 8.4% [125]. In the Reduction by Dutasteride of Prostate Cancer Events (REDUCE) study, an international multicentre chemoprevention trial of 3508 subjects, the HOXB13 G84E mutation was only present in Caucasians, with the highest prevalence in Northern Europeans, followed by Western Europeans and North Americans with no carriers identified in Africa, Australia, Latin America and the rest of the European population [124]. A number of studies have confirmed an increased risk of prostate cancer in patients with the HOXB13 G84E variant [116, 122, 124, 126]. In a study of 5083 unrelated subjects with prostate cancer and 1401 controls, there was a 20-fold increase in the frequency of the HOXB13 G84E mutation in men with prostate cancer compared with those without it (1.4 versus 0.1 percent) [116]. Similarly, in the 4-year follow-up of the REDUCE study, the prostate cancer detection rate was 53.8% among mutation carriers and 22.0% among noncarriers, with a relative risk of 2.45 [124]. In a second case-control study of familial prostate cancer, investigators genotyped 928 familial prostate cancer probands and 930 control probands without a personal or family history of prostate cancer and found the point estimate of the odds ratio, adjusted for age, was 7.9 among carriers of the mutation [122]. The estimate was greater among cases with a family history of three or more relatives affected (OR = 11.8), compared to a family history of only two affected (OR = 5.8). In a British case-control study assessing the prevalence of HOXB13 G84E, investigators identified the variant in 0.5% of healthy controls and 1.5% of prostate cancer cases and found the presence of HOXB13 G84E to be associated with a 2.93-fold increased risk of prostate cancer [126]. The risk was even higher among men with family history of prostate cancer supporting the hereditary link.

Table 5.5 HOXB13 and risk of prostate cancer

The penetrance estimates for prostate cancer development in HOXB13 G84E mutation carriers have also been reported. A study from Sweden found HOXB13 G84E to be prevalent in more than 1% of the population and to be associated with a 3.5-fold increased risk of prostate cancer with an estimated 33% lifetime risk of prostate cancer [127]. Furthermore, an Australian study reported age-specific cumulative risk of prostate cancer of up to 60% by the age 80 years [128].

HOXB13 expression has been linked to advanced pT stage, high Gleason grade, positive lymph node status, high preoperative PSA levels, TMPRSS2:ERG fusion, PTEN deletions, AR expression, cell proliferation, reduced PSA expression and early PSA recurrence; however, it has not been found to have an effect on prognostic outcomes and overall or cancer-specific survival [126, 131, 132]. It has also been demonstrated that the prostate cancer risk-associated T allele of rs339331 enhances HOXB13 chromatin binding and drives allele-specific upregulation of the rs339331-associated gene RFX6 which might have a role in prostate cancer cellular transformation [130]. It appears that HOXB13 has an important role in prostate cancer development; however, the mechanism by which it contributes to the pathogenesis of prostate cancer remains unknown.

Mismatch Repair (MMR) Genes and Prostate Cancer

Lynch Syndrome

Lynch syndrome is an autosomal dominant disorder caused by a germline mutation in one of the mismatch repair (MMR) genes , MLH1, MSH2, MSH6 or PMS2 [133]. Chromosomal deletion, point mutation or epigenetic inactivation by hypermethylation in a second allele predisposes to a lack of MMR protein function, leading to an accumulation of mutations [134]. This can lead to malignant transformation of cells and tumour formation with a mutated phenotype, demonstrated by the presence of microsatellite instability (MSI) and lack of one or more of the four MMR proteins on staining by immunohistochemistry (IHC) [135]. There is an increased risk of several cancers in patients with Lynch syndrome including colorectal, endometrial, ovarian, gastric, small intestinal, pancreatic, ureteral, brain and sebaceous gland adenocarcinomas [136]. Screening for colorectal cancer and prophylactic surgery for gynaecological cancers have been shown to improve outcomes in these patients [137, 138]. Prostate cancer is currently not considered part of the Lynch syndrome spectrum, and data for the association has been inconclusive [139,140,141]. However, a number of studies have shown the cumulative lifetime risk of prostate cancer to be increased in individuals with Lynch syndrome, ranging from twofold to fivefold higher than in the general population [142,143,144,145].

Loss of MMR protein expression has been shown in prostate cancer tumours in patients with Lynch syndrome [146, 147]; however, this has been rarely detected in patients with hereditary prostate cancer [148], suggesting that Lynch syndrome is unlikely to be implicated in the majority of cases of familial prostate cancer [139]. Furthermore, patients with Lynch syndrome do not appear to have an earlier onset of prostate cancer or a more aggressive phenotype [143].

MSH2

There is some evidence that prostate cancer is more commonly diagnosed in men with an MSH2 mutation compared to men with a mutation in one of the other MMR genes [142, 143, 149,150,151,152]. A German study identified cases of prostate cancer among men who were positive or obligate carriers of MSH2 mutations; however, they found no increased incidence of prostate cancer [153]. The investigators noted a median age of 59 years at diagnosis, younger than the average age at diagnosis, suggesting a marginal association between MSH2 mutation and risk of prostate cancer. Rosty et al. have shown that MMR gene mutation carriers have at least a twofold or greater increased risk of developing MMR-deficient prostate cancer, with the risk being highest for MSH2 mutation carriers [154]. Except for Rosty et al. most studies have been underpowered to observe any differences in prostate cancer risk by specific MMR gene mutations [145]. Large cohorts will be required to measure separate prostate cancer risks for specific MMR gene mutation carriers.

Fanconi Anaemia

Fanconi anaemia (FA) is a rare disorder of chromosomal instability characterized by bone marrow failure, developmental anomalies and an increased incidence of myelodysplasia, leukaemia and solid tumours [155, 156]. The prevalence of FA is 1–5 cases per 1 million persons, and the heterozygous carrier frequency is about 1 case per 300 persons [157]. Germline mutations, somatic mutations and epigenetic silencing have all been shown to occur in FA genes [158]. FA is caused by biallelic mutation of any 1 of the 16 known genes and can be either autosomal or X-linked recessive, depending on the inherited gene. Of the 16 genes (FANCA, FANCB, FANCC, FANCD1/BRCA2, FANCD2, FANCE, FANCF, FANCG, FANCI, FANCL, FANCM, FANCN/PALB2, FANCJ/BRIP1, FANCO/RAD51C, FANCP/SLX4 and FANCQ/ERCC4), three of them, FANCD1, FANCN and FANCJ, are identical to the DNA repair genes BRCA2, PALB2 and BRIP1 [159,160,161]. The protein products of these genes function cooperatively in the FA-BRCA pathway which plays a central role in DNA repair and the maintenance of genomic integrity [159].

The FA Pathway

After DNA damage, FA proteins form a nuclear complex that mediates the monoubiquitylation of the FA protein FANCD2 [159,160,161]. This monoubiquitylated FANCD2 colocalizes in nuclear foci with proteins involved in DNA repair, including BRCA1, FANCD1/BRCA2, FANCN/PALB2 and RAD51 [161,162,163,164,165,166,167,168]. FANCJ interacts directly with BRCA1 and is a member of the DNA helicase family [169]. FANCN interacts with FANCD1/BRCA2 and is required for its homologous recombination and checkpoint functions [170]. In the absence of an intact FA pathway, cells are sensitive to spontaneous and DNA damage-induced chromosomal breaks leading to tumourigenesis [171]. Clinical trials are now testing the use of PARP inhibitors in patients with FA pathway defects [172].

FA Genes and Prostate Cancer

Initial studies of cancer risk in FA heterozygotes found a higher rate of cancers; however, subsequent studies have not confirmed this risk [173,174,175,176]. Due to the conflicting data from other studies and the relative rarity of FA, it is difficult to confirm these findings. In a British study of FA families, there was no higher incidence of cancer detected; however, 2 prostate cancer cases were observed in 33 obligate carriers, with an overall relative risk of prostate cancer in carriers which was calculated to be 3.089, an incidence which was higher than expected [177]. In a founder population cohort study of Finnish FA patients, the prevalence of 6 FA-causing mutations in over 1800 breast cancer and 565 prostate cancer cases was analysed [178]. All mutations were recurrent, but no significant association with cancer susceptibility was observed for any. Further analysis from the prostate cancer cohort revealed several carriers both among affected and unaffected males, but the frequencies were roughly the same and without any statistical significance. Although clearly deleterious, the tested heterozygous mutations in the FA pathway do not act as high- or moderate-risk alleles for prostate cancer in the general population; however, there could be a modest increased risk in prostate cancer in some FA heterozygotes which merits further investigation in larger cohort studies [179].

DNA Adducts

Polycyclic aromatic hydrocarbons (PAH) and heteroc yclic amines (HCA) are environmental contaminants and known carcinogens (1). PAHs and HCAs are thought to derive their carcinogenic properties through their ability to form DNA adducts. 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is the major HCA generated from cooking meats at high temperatures, and exposure has been shown to induce prostate cancer in animal studies. PhIP induces cancer by the formation of PhIP-DNA adducts [180]. This formation of DNA adducts can lead to DNA replication errors and increase the potential for carcinogenesis. DNA adducts have been detected in prostate cells, but the exact nature of adducts with respect to prostate cancer risk factors and histology is unclear [181]. African ancestry is strongly associated with PhIP-DNA adduct levels in non-tumour prostate cells [182]. Furthermore, the SULT1A1 genotype and enzyme activity has been suggested to be associated with DNA adduct levels and ethnicity [183]. However, further studies indicate the SULT1A1 genotype does not appear to be associated with increased genetic susceptibility to prostate cancer [182, 184], and overall, elevated levels of PhIP-DNA adducts do not appear to significantly increase prostate cancer risk, independent of ethnicity [185].

Conclusion

Case-control studies, linkage analyses , admixture mapping and GWAS have identified a number of candidate genes associated with prostate cancer susceptibility. Similarly, studies of ethnic and founder populations have identified inherited genetic factors associated with a higher risk of prostate cancer. However, the replication of these findings remains inconsistent, with numerous genes likely to be involved. GWAS have provided evidence supporting the genetic complexity of prostate cancer. It is also likely that there could be significant variation in the contribution of various genes and SNPs to prostate cancer risk in various ethnic groups. Additional studies will be required to determine whether genes or SNPs can be combined with PSA levels and other clinical factors to identify men who are at particularly high risk of being diagnosed with prostate cancer. The finding that the FA–BRCA pathway is intimately involved in the response to DNA damage and repair and may confer potential susceptibility to prostate cancer has spurred further research in this area. Furthermore, tumour cells with a disrupted DNA repair pathway are hypersensitive to PARP inhibitors, and these agents have been shown to be efficacious in prostate cancer. Moving forward, genes identified through GWAS may eventually have a role in prostate cancer screening and as targets for therapeutic targets.