Genetic landscape of homologous recombination repair genes in early-onset/familial prostate cancer patients

Prostate cancer (PrCa) is one of the three most frequent and deadliest cancers worldwide. The discovery of PARP inhibitors for the treatment of tumors with deleterious variants in homologous recombination repair (HRR) genes has placed PrCa on the roadmap of precision medicine. However, the overall contribution of HRR genes to the 10%-20% of carcinomas arising in men with early-onset/familial PrCa has not been fully clarified. We used targeted next-generation sequencing (T-NGS) covering eight HRR genes (ATM, BRCA1, BRCA2, BRIP1, CHEK2, NBN, PALB2, and RAD51C) and an analysis pipeline querying both small and large genomic variations to clarify their global and relative contribution to hereditary PrCa predisposition in a series of 462 early-onset/familial PrCa cases. Deleterious variants were found in 3.9% of the patients, with CHEK2 and ATM being the most frequently mutated genes (38.9% and 22.2% of the carriers, respectively), followed by PALB2 and NBN (11.1% of the carriers, each), and finally by BRCA2, RAD51C, and BRIP1 (5.6% of the carriers, each). Using the same NGS data, exonic rearrangements were found in two patients, one pathogenic in BRCA2 and one of unknown significance in BRCA1. These results contribute to clarify the genetic heterogeneity that underlies PrCa predisposition in the early-onset and familial disease, respectively.

Motivation and family communication in hereditary prostate cancer genetic testing: Survey of patients from a US tertiary medical center

Identification of a hereditary prostate cancer in an affected individual can guide treatment and may also impact cancer screening and surveillance for patients and their relatives. This study aimed to determine the factors that are associated with the decision-making process of individuals with prostate cancer regarding whether to pursue genetic testing as well as how, why, and with whom genetic test results are shared. We surveyed 113 patients diagnosed with prostate cancer who received cancer genetic counseling through a United States tertiary medical center, inquiring about genetic testing motivations and family communication about results. Among those who pursued genetic testing, (1) learning about my family's possible cancer risk (98%), (2) learning information that may guide cancer treatment (93%), and (3) learning if I am at risk for future cancers (92%) were most frequently identified as slightly or very important factors in their decision. Participants shared their genetic test results in a higher proportion to male first-degree relatives than female first-degree relatives; however, no significant difference was found (p = 0.103). Our study may suggest sex differences related to family communication about genetic testing results. Such findings indicate a critical need for genetic counselors to clearly communicate the impact of genetic test results on both male and female relatives. Further research on motivation and family communication about genetic test results in diverse cohorts is needed.

Hereditary Prostate Cancer: Genes Related, Target Therapy and Prevention

Prostate cancer (PCa) is globally the second most diagnosed cancer type and the most common cause of cancer-related deaths in men. Family history of PCa, hereditary breast and ovarian cancer (HBOC) and Lynch syndromes (LS), are among the most important risk factors compared to age, race, ethnicity and environmental factors for PCa development. Hereditary prostate cancer (HPCa) has the highest heritability of any major cancer in men. The proportion of PCa attributable to hereditary factors has been estimated in the range of 5–15%. To date, the genes more consistently associated to HPCa susceptibility include mismatch repair (MMR) genes (MLH1, MSH2, MSH6, and PMS2) and homologous recombination genes (BRCA1/2, ATM, PALB2, CHEK2). Additional genes are also recommended to be integrated into specific research, including HOXB13, BRP1 and NSB1. Importantly, BRCA1/BRCA2 and ATM mutated patients potentially benefit from Poly (ADP-ribose) polymerase PARP inhibitors, through a mechanism of synthetic lethality, causing selective tumor cell cytotoxicity in cell lines. Moreover, the detection of germline alterations in MMR genes has therapeutic implications, as it may help to predict immunotherapy benefits. Here, we discuss the current knowledge of the genetic basis for inherited predisposition to PCa, the potential target therapy, and the role of active surveillance as a management strategy for patients with low-risk PCa. Finally, the current PCa guideline recommendations are reviewed.

Prostate Cancer Genomics: Recent Advances and the Prevailing Underrepresentation from Racial and Ethnic Minorities

Prostate cancer (CaP) is the most commonly diagnosed non-cutaneous cancer and the second leading cause of male cancer deaths in the United States. Among African American (AA) men, CaP is the most prevalent malignancy, with disproportionately higher incidence and mortality rates. Even after discounting the influence of socioeconomic factors, the effect of molecular and genetic factors on racial disparity of CaP is evident. Earlier studies on the molecular basis for CaP disparity have focused on the influence of heritable mutations and single-nucleotide polymorphisms (SNPs). Most CaP susceptibility alleles identified based on genome-wide association studies (GWAS) were common, low-penetrance variants. Germline CaP-associated mutations that are highly penetrant, such as those found in HOXB13 and BRCA2, are usually rare. More recently, genomic studies enabled by Next-Gen Sequencing (NGS) technologies have focused on the identification of somatic mutations that contribute to CaP tumorigenesis. These studies confirmed the high prevalence of ERG gene fusions and PTEN deletions among Caucasian Americans and identified novel somatic alterations in SPOP and FOXA1 genes in early stages of CaP. Individuals with African ancestry and other minorities are often underrepresented in these large-scale genomic studies, which are performed primarily using tumors from men of European ancestry. The insufficient number of specimens from AA men and other minority populations, together with the heterogeneity in the molecular etiology of CaP across populations, challenge the generalizability of findings from these projects. Efforts to close this gap by sequencing larger numbers of tumor specimens from more diverse populations, although still at an early stage, have discovered distinct genomic alterations. These research findings can have a direct impact on the diagnosis of CaP, the stratification of patients for treatment, and can help to address the disparity in incidence and mortality of CaP. This review examines the progress of understanding in CaP genetics and genomics and highlight the need to increase the representation from minority populations.

The clinical phenotype of hereditary versus sporadic prostate cancer: HPC definition revisited

BACKGROUND

The definition of hereditary prostate cancer (HPC) is based on family history and age at onset. Intuitively, HPC is a serious subtype of prostate cancer but there are only limited data on the clinical phenotype of HPC. Here, we aimed to compare the prognosis of HPC to the sporadic form of prostate cancer (SPC).

METHODS

HPC patients were identified through a national registry of HPC families in the Netherlands, selecting patients diagnosed from the year 2000 onward (n = 324). SPC patients were identified from the Netherlands Cancer Registry (NCR) between 2003 and 2006 for a population-based study into the genetic susceptibility of PC (n = 1,664). Detailed clinical data were collected by NCR-registrars, using a standardized registration form. Follow-up extended up to the end of 2013. Differences between the groups were evaluated by cross-tabulations and tested for statistical significance while accounting for familial dependency of observations by GEE. Differences in progression-free and overall survival were evaluated using χ(2) testing with GEE in a proportional-hazards model.

RESULTS

HPC patients were on average 3 years younger at diagnosis, had lower PSA values, lower Gleason scores, and more often locally confined disease. Of the HPC patients, 35% had high-risk disease (NICE-criteria) versus 51% of the SPC patients. HPC patients were less often treated with active surveillance. Kaplan-Meier 5-year progression-free survival after radical prostatectomy was comparable for HPC (78%) and SPC (74%; P = 0.30). The 5-year overall survival was 85% (95%CI 81-89%) for HPC versus 80% (95%CI 78-82%) for SPC (P = 0.03).

CONCLUSIONS

HPC has a favorable clinical phenotype but patients more often underwent radical treatment. The major limitation of HPC is the absence of a genetics-based definition of HPC, which may lead to over-diagnosis of PC in men with a family history of prostate cancer. The HPC definition should, therefore, be re-evaluated, aiming at a reduction of over-diagnosis and overtreatment among men with multiple relatives diagnosed with PC. Prostate 76:897-904, 2016. © 2016 The Authors. The Prostate published by Wiley Periodicals, Inc.

Confirmation of genetic variants associated with lethal prostate cancer in a cohort of men from hereditary prostate cancer families

Germline genetic variants have been suggested as prognostic biomarkers for identifying patients at high risk for lethal prostate cancer (PCa). Validation studies have confirmed the association of several single nucleotide polymorphisms (SNPs) with fatal PCa, but whether these variants affect PCa-specific mortality (PCSM) in patients with an inherited predisposition to PCa, based on familial history, is unknown. For this study, a cohort of 957 PCa patients from 270 hereditary prostate cancer families of European ancestry was genotyped for a panel of 22 PCSM-associated SNPs. Death certificates were reviewed to confirm cause of death. Mixed-effect Cox proportional hazards models were used to assess survival according to genotypes, accounting for relatedness and clinicopathological factors. Within this cohort, 98 PCa deaths were confirmed over an average follow-up period of 12.7 years after diagnosis. Variant allele carriers for three SNPs had significantly altered risk for PCSM [rs635261 at RNASEL, hazard ratio (HR), 0.35, 95% CI, 0.18-0.66; p = 0.002; rs915927 in XRCC1, HR, 1.91, 95% CI, 1.21-3.02; p = 0.009; and rs2494750 at AKT1, HR, 0.45, 95% CI, 0.23-0.90; p = 0.016). These results confirm the association of genetic variation in three genes with PCa lethality in a cohort of men with an inherited susceptibility to the disease and provide validation evidence that germline SNPs provide prognostic information for PCa patients. Development of a panel of germline biomarkers with clinical utility for distinguishing patients at detection who have an increased risk for fatal PCa is warranted.

Analysis of the gene coding for the BRCA2-interacting protein PALB2 in hereditary prostate cancer

BACKGROUND

The genetic basis of susceptibility to prostate cancer (PRCA) remains elusive. Mutations in BRCA2 have been associated with increased prostate cancer risk and account for around 2% of young onset (<56 years) prostate cancer cases. PALB2 is a recently identified breast cancer susceptibility gene whose protein is closely associated with BRCA2 and is essential for BRCA2 anchorage to nuclear structures. This functional relationship made PALB2 a candidate PRCA susceptibility gene.

METHODS

We sequenced PALB2 in probands from 95 PRCA families, 77 of which had two or more cases of early onset PRCA (age at diagnosis <55 years), and the remaining 18 had one case of early onset PRCA and five or more total cases of PRCA.

RESULTS

Two previously unreported variants, K18R and V925L were identified, neither of which is in a known PALB2 functional domain and both of which are unlikely to be pathogenic. No truncating mutations were identified.

CONCLUSIONS

These results indicate that deleterious PALB2 mutations are unlikely to play a significant role in hereditary prostate cancer.

A common nonsense mutation in EphB2 is associated with prostate cancer risk in African American men with a positive family history

BACKGROUND

The EphB2 gene was recently implicated as a prostate cancer (PC) tumour suppressor gene, with somatic inactivating mutations occurring in approximately 10% of sporadic tumours. We evaluated the contribution of EphB2 to inherited PC susceptibility in African Americans (AA) by screening the gene for germline polymorphisms.

METHODS

Direct sequencing of the coding region of EphB2 was performed on 72 probands from the African American Hereditary Prostate Cancer Study (AAHPC). A case-control association analysis was then carried out using the AAHPC probands and an additional 183 cases of sporadic PC compared with 329 healthy AA male controls. In addition, we performed an ancestry adjusted association study where we adjusted for individual ancestry among all subjects, in order to rule out a spurious association due to population stratification.

RESULTS

Ten coding sequence variants were identified, including the K1019X (3055A-->T) nonsense mutation which was present in 15.3% of the AAHPC probands but only 1.7% of 231 European American (EA) control samples. We observed that the 3055A-->T mutation significantly increased risk for prostate cancer over twofold (Fisher's two sided test, p = 0.003). The T allele was significantly more common among AAHPC probands (15.3%) than among healthy AA male controls (5.2%) (odds ratio 3.31; 95% confidence interval 1.5 to 7.4; p = 0.008). The ancestry adjusted analyses confirmed the association.

CONCLUSIONS

Our data show that the K1019X mutation in the EphB2 gene differs in frequency between AA and EA, is associated with increased risk for PC in AA men with a positive family history, and may be an important genetic risk factor for prostate cancer in AA.