Stephen M. Edwards

Multiple newly identified loci associated with prostate cancer susceptibility

Prostate cancer is the most common cancer affecting males in developed countries. It shows consistent evidence of familial aggregation, but the causes of this aggregation are mostly unknown. To identify common alleles associated with prostate cancer risk, we conducted a genome-wide association study (GWAS) using blood DNA samples from 1,854 individuals with clinically detected prostate cancer diagnosed at ≤60 years or with a family history of disease, and 1,894 population-screened controls with a low prostate-specific antigen (PSA) concentration (<0.5 ng/ml). We analyzed these samples for 541,129 SNPs using the Illumina Infinium platform. Initial putative associations were confirmed using a further 3,268 cases and 3,366 controls. We identified seven loci associated with prostate cancer on chromosomes 3, 6, 7, 10, 11, 19 and X (P = 2.7 × 10−8 to P = 8.7 × 10−29). We confirmed previous reports of common loci associated with prostate cancer at 8q24 and 17q. Moreover, we found that three of the newly identified loci contain candidate susceptibility genes: MSMB, LMTK2 and KLK3.

Two Percent of Men with Early-Onset Prostate Cancer Harbor Germline Mutations in the BRCA2 Gene

Studies of families with breast cancer have indicated that male carriers of BRCA2 mutations are at increased risk of prostate cancer, particularly at an early age. To evaluate the contribution of BRCA2 mutations to early-onset prostate cancer, we screened the complete coding sequence of BRCA2 for germline mutations, in 263 men with diagnoses of prostate cancer who were </=55 years of age. Protein-truncating mutations were found in six men (2.3%; 95% confidence interval 0.8%-5.0%), and all of these mutations were clustered outside the ovarian-cancer cluster region. The relative risk of developing prostate cancer by age 56 years from a deleterious germline BRCA2 mutation was 23-fold. Four of the patients with mutations did not have a family history of breast or ovarian cancer. Twenty-two variants of uncertain significance were also identified. These results confirm that BRCA2 is a high-risk prostate-cancer-susceptibility gene and have potential implications for the management of early-onset prostate cancer, in both patients and their relatives.

Multiple Loci With Different Cancer Specificities Within the 8q24 Gene Desert

Recent studies based on genome-wide association, linkage, and admixture scan analysis have reported associations of various genetic variants in 8q24 with susceptibility to breast, prostate, and colorectal cancer. This locus lies within a 1.18-Mb region that contains no known genes but is bounded at its centromeric end by FAM84B and at its telomeric end by c-MYC, two candidate cancer susceptibility genes. To investigate the associations of specific loci within 8q24 with specific cancers, we genotyped the nine previously reported cancer-associated single-nucleotide polymorphisms across the region in four case-control sets of prostate (1854 case subjects and 1894 control subjects), breast (2270 case subjects and 2280 control subjects), colorectal (2299 case subjects and 2284 control subjects), and ovarian (1975 case subjects and 3411 control subjects) cancer. Five different haplotype blocks within this gene desert were specifically associated with risks of different cancers. One block was solely associated with risk of breast cancer, three others were associated solely with the risk of prostate cancer, and a fifth was associated with the risk of prostate, colorectal, and ovarian cancer, but not breast cancer. We conclude that there are at least five separate functional variants in this region.

Androgen receptor polymorphisms: Association with prostate cancer risk, relapse and overall survival

Several reports have suggested that one or both of the trinucleotide repeat polymorphisms in the human androgen receptor (hAR) gene, (CAG)n coding for polyglutamine and (GGC)ncoding for polyglycine, may be associated with prostate cancer risk; but no study has investigated their association with disease progression. We present here a study of both hAR trinucleotide repeat polymorphisms not only as they relate to the initial diagnosis but also as they are associated with disease progression after therapy. Lymphocyte DNA samples from 178 British Caucasian prostate cancer patients and 195 control individuals were genotyped by PCR for the (CAG)n and (GGC)n polymorphisms in hAR. Univariate Cox proportional hazard analysis indicated that stage, grade and GGC repeat length were individually significant factors associated with disease‐free survival (DFS) and overall survival (OS). The relative risk (RR) of relapse for men with more than 16 GGC repeats was 1.74 (95% CI 1.08–2.79) and of dying from any cause, 1.98 (1.13–3.45). Adjusting for stage and grade, GGC effects remained but were not significant (RRDFS= 1.60, p = 0.052; RROS= 1.65, p = 0.088). The greatest effects were in stage T1‐T2 (RRDFS= 3.56, 95% CI 1.13–11.21) and grade 1 (RRDFS= 6.47, 95% CI 0.57–72.8) tumours. No differences between patient and control allele distributions were found by odds‐ratio analysis, nor were trends with stage or grade evident in the proportion of short CAG alleles. Non‐significant trends with stage and grade were found in the proportion of short GGC alleles. The (GGC)n polymorphism in this population is a significant predictor of disease outcome. Since the (GGC)n effect is strongest in early‐stage tumours, this marker may help forecast aggressive behaviour and could be used to identify those patients meriting more radical treatment. Int. J. Cancer (Pred. Oncol.) 84:458–465, 1999.

Multiple Novel Prostate Cancer Predisposition Loci Confirmed by an International Study: The PRACTICAL Consortium

A recent genome-wide association study found that genetic variants on chromosomes 3, 6, 7, 10, 11, 19 and X were associated with prostate cancer risk. We evaluated the most significant single-nucleotide polymorphisms (SNP) in these loci using a worldwide consortium of 13 groups (PRACTICAL). Blood DNA from 7,370 prostate cancer cases and 5,742 male controls was analyzed by genotyping assays. Odds ratios (OR) associated with each genotype were estimated using unconditional logistic regression. Six of the seven SNPs showed clear evidence of association with prostate cancer (P = 0.0007-P = 10−17). For each of these six SNPs, the estimated per-allele OR was similar to those previously reported and ranged from 1.12 to 1.29. One SNP on 3p12 (rs2660753) showed a weaker association than previously reported [per-allele OR, 1.08 (95% confidence interval, 1.00-1.16; P = 0.06) versus 1.18 (95% confidence interval, 1.06-1.31)]. The combined risks associated with each pair of SNPs were consistent with a multiplicative risk model. Under this model, and in combination with previously reported SNPs on 8q and 17q, these loci explain 16% of the familial risk of the disease, and men in the top 10% of the risk distribution have a 2.1-fold increased risk relative to general population rates. This study provides strong confirmation of these susceptibility loci in multiple populations and shows that they make an important contribution to prostate cancer risk prediction. (Cancer Epidemiol Biomarkers Prev 2008;17(8):2052–61)

Unravelling the genetics of prostate cancer

This review describes what is currently known about the genetics of prostate cancer. Traditionally, the genetics of a suspected inherited cancer predisposition have generally been thought of in terms of a single, high‐risk gene with a dominant mode of inheritance. Such a gene might be observed in families, as has been documented in familial breast cancer (BRCA1/2), familial colorectal cancer (HNPCC), retinoblastoma (RB1), and Wilms tumor (WT1). This review investigates the evidence for the existence, first of familial prostate cancer, and second, for the presence of such a high‐risk gene in those families by epidemiological and experimental approaches. Another current area of interest in prostate cancer is the investigation of the contribution of common lower penetrance genes to the disease. This alternative approach has become popular, as it raises the issue of frequently seen genetic variations such as single nucleotide polymorphisms (SNPs) having relevance to the risk of developing the disease. Finally, this article will explore the way forward, with emphasis on worldwide collaboration from teams attempting to find the genes responsible for the disease and investment in new technologies that will aid in their discovery.

ATM polymorphisms as risk factors for prostate cancer development

The risk of prostate cancer is known to be elevated in carriers of germline mutations in BRCA2, and possibly also in carriers of BRCA1 and CHEK2 mutations. These genes are components of the ATM-dependent DNA damage signalling pathways. To evaluate the hypothesis that variants in ATM itself might be associated with prostate cancer risk, we genotyped five ATM variants in DNA from 637 prostate cancer patients and 445 controls with no family history of cancer. No significant differences in the frequency of the variant alleles at 5557G>A (D1853N), 5558A>T (D1853V), ivs38-8t>c and ivs38-15g>c were found between the cases and controls. The 3161G (P1054R) variant allele was, however, significantly associated with an increased risk of developing prostate cancer (any G vs CC OR 2.13, 95% CI 1.17–3.87, P=0.016). A lymphoblastoid cell line carrying both the 3161G and the 2572C (858L) variant in the homozygote state shows a cell cycle progression profile after exposure to ionising radiation that is significantly different to that seen in cell lines carrying a wild-type ATM gene. These results provide evidence that the presence of common variants in the ATM gene, may confer an altered cellular phenotype, and that the ATM 3161C>G variant might be associated with prostate cancer risk.

Immunohistochemical expression of BRCA2 protein and allelic loss at the BRCA2 locus in prostate cancer

Many epidemiological studies have reported an association between breast and prostate cancer. BRCA2 functions as a tumour‐suppressor gene in about 35% of large familial breast‐cancer clusters; its role in the pathogenesis of sporadic breast cancer is less clear. We have evaluated immunohistochemical expression of BRCA2 protein and allelic loss of markers at the BRCA2 locus in tissue derived both from sporadic and from familial cases of prostate cancer. Immunohistochemical analysis was performed in 167 paraffin‐embedded archival specimens. Normal prostate and 75% (120/160) of prostate‐cancer tissue did not express BRCA2 protein. However, 25% (40/160) of cancer cases did express patchy staining; of these, 17% (27/160) expressed positive nuclear staining in normal glandular tissue adjacent to tumour (either in addition to, or, independent of tumour). Allelic loss is the hallmark of a tumour‐suppressor gene. Markers flanking (D13S267, D13S260) and within (D13S171) the BRCA2 gene indicated allelic loss in at least one locus in 23% (17/73) of tumours analyzed. There was no difference in the rates of allelic loss between sporadic and familial tumours, nor was there any association between immunohistochemical staining and allelic loss. Although immunohistochemical staining provided no useful prognostic information, allelic loss at BRCA2 was shown in univariate analysis to be associated with poorer survival (log‐rank test, p = 0.046). Int. J. Cancer 78:1–7, 1998.© 1998 Wiley‐Liss, Inc.

Macrophage Scavenger Receptor 1 999C>T (R293X) Mutation and Risk of Prostate Cancer

Background: Variants in the gene encoding the macrophage scavenger receptor 1 (MSR14) protein have been identified in men with prostate cancer, and several small studies have suggested that the 999C>T (R293X) protein-truncating mutation may be associated with an increased risk for this disease. Methods: Using large case-control, cohort, and prostate cancer family studies conducted in several Western countries, we tested for the 999C>T mutation in 2,943 men with invasive prostate carcinoma, including 401 males from multiple-case families, 1,982 cases unselected for age, and 575 men diagnosed before the age of 56 years, and in 2,870 male controls. Risk ratios were estimated by unconditional logistic regression adjusting for country and by a modified segregation analysis. A meta-analysis was conducted pooling our data with published data. Results: The prevalence of MSR1*999C>T mutation carriers was 0.027 (SE, 0.003) in cases and 0.022 (SE, 0.002) in controls, and did not differ by country, ethnicity, or source. The adjusted risk ratio for prostate cancer associated with being a 999C>T carrier was 1.31 [95% confidence interval (CI), 0.93-1.84; P = 0.16]. The modified segregation analysis estimated the risk ratio to be 1.20 (95% CI, 0.87-1.66; P = 0.16). The risk ratio estimated from the meta-analysis was 1.34 (95% CI, 0.94-1.89; P = 0.10). Conclusion: Our large-scale analysis of case and controls from several countries found no evidence that the 999C>T mutation is associated with increased risk of prostate cancer. The meta-analysis suggests it is unlikely that this mutation confers more than a 2-fold increased risk.

Identification of new genetic risk factors for prostate cancer.

There is evidence that a substantial part of genetic predisposition to prostate cancer (PCa) may be due to lower penetrance genes which are found by genome-wide association studies. We have recently conducted such a study and seven new regions of the genome linked to PCa risk have been identified. Three of these loci contain candidate susceptibility genes: MSMB, LMTK2 and KLK2/3. The MSMB and KLK2/3 genes may be useful for PCa screening, and the LMTK2 gene might provide a potential therapeutic target. Together with results from other groups, there are now 23 germline genetic variants which have been reported. These results have the potential to be developed into a genetic test. However, we consider that marketing of tests to the public is premature, as PCa risk can not be evaluated fully at this stage and the appropriate screening protocols need to be developed. Follow-up validation studies, as well as studies to explore the psychological implications of genetic profile testing, will be vital prior to roll out into healthcare.