Prevalence of Germline BRCA1/2 Variants in Ashkenazi and Non-Ashkenazi Prostate Cancer Populations: A Systematic Review and Meta-Analysis

Simple Summary Germline BRCA2 pathogenic variant carriers are associated with prostate cancer risk. Ashkenazi Jewish people are at higher risk of breast cancer due to the high prevalence of specific founder germline BRCA1/2 variants. The distribution of these variants (BRCA1 vs. BRCA2) in Ashkenazi men with prostate cancer is not clear. This systematic review and meta-analysis indicates that germline BRCA1 variants are higher in the Ashkenazi Jewish ethnicity in comparison to non-Ashkenazi men. Instead, BRCA2 variants present a similar distribution between the two considered groups. Abstract Background and aims: International guidelines recommend testing BRCA2 in men with prostate cancer, due to the presence of a strong association with this gene. Some ethnicities present disparities in genetic distribution for the relation with specific founder variants. Ashkenazi Jewish people are, importantly, at high risk of breast cancer for their inherited cluster with germline BRCA1/2 variants. However, in Ashkenazi men with prostate cancer, the prevalence of BRCA1 and/or BRCA2 is not well defined. We assessed the frequency of these variants in Ashkenazi vs. non-Ashkenazi men with prostate cancer. Materials and Methods: In accord with the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) statement, we revised all germline BRCA variants reported in MEDLINE from 1996 to 2021 in Ashkenazi and non-Ashkenazi men with prostate cancer. Results: Thirty-five original studies were selected for the analysis. Among populations from Israel and North America, Ashkenazi Jewish men presented higher prevalence of BRCA1 variants [0.9% (0.4–1.5) vs. 0.5% (0.2–1.1), p = 0.09] and a lower prevalence of BRCA2 variants [1.5% (1.1–2.0) vs. 3.5% (1.7–5.9), p = 0.08] in comparison to the non-Ashkenazi population. Conclusions: Since germline BRCA1 variants are more prevalent and BRCA2 variants are less prevalent in PCa patients of Ashkenazi Jewish ethnicity in comparison to non-Ashkenazi patients, prostate cancer genetic screening in Ashkenazi men should not be restricted to the BRCA2 gene.


Introduction
Prostate cancer (PCa) is the second most commonly diagnosed cancer in men, accounting for 15% of all male cancers [1]. Family history and ethnic background are associated with an increased incidence, even if defined hereditary disease is present in only about 10% of men with PCa [2,3].

Introduction
Prostate cancer (PCa) is the second most commonly diagnosed cancer in men, accounting for 15% of all male cancers [1]. Family history and ethnic background are associated with an increased incidence, even if defined hereditary disease is present in only about 10% of men with PCa [2,3].
Many factors have been associated with the risk of PCa or as being important for disease progression [4]. Obesity has been associated with an increased risk of high-grade PCa [5], and high alcohol intake has been associated with a higher risk of PCa and PCaspecific mortality [6]. An organized program of PCa screening may contribute to a further 5-10% reduction in cancer mortality [7,8].
Inherited PCa predisposition accounts in about 10% of families [9]. Genetic screening demonstrated a strong association with germline BRCA2 mutations and PCa risk. However, there are no standardized measures for risk containing in asymptomatic highrisk individuals [10].
Ashkenazi Jewish people have high breast cancer (BC) risk due to the high penetrance of some specific germline BRCA variants in their ancestry, in particular c.185delA/ 5382insC for BRCA1 and c.6174delT for BRCA2 [11]. In BC Ashkenazi Jewish people with positive germline BRCA1/2 variants, BRCA1 is prevalent (71%) in comparison to BRCA2 (29%) [12]. The global prevalence of BRCA1/2 variants in Ashkenazi Jewish people with PCa is undefined. With the present study, we revised the prevalence of germline BRCA1/2 variants in Ashkenazi and non-Ashkenazi populations using a systematic review and meta-analysis approach.

Data Retrieval
We used the checklist of items in accordance with the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) statement ( Figure 1). We revised all germline BRCA variants reported in MEDLINE from 1996 to 2021, including original reports and literature reviews edited in English language. We used the following PubMed query for the initial search: "[Prostate cancer and (BRCA OR BRCA1 OR BRCA2)] AND 1996/01:2021/12[EDAT]". We also reviewed references and citations of key articles and previous meta-analyses on the association between BRCA1/2 variants and PCa using Scopus. The analysis was limited to studies involving subjects affected by PCa screened for germline BRCA variants ( Figure 1). This study was not registered.

Study Selection
Original studies that contained information on both germline BRCA1/2 and PCa were considered. Case series, editorials, case reports, and congress abstracts were excluded. Titles and abstracts were screened by two authors to determine whether studies met the eligibility criteria for full-text assessment, and a sample of 25% was screened independently by another author as a quality assurance process. The full-text assessment was conducted by two authors with consultation from a third author if required. Full-text publications in English were considered. Case series, editorials, case reports, and congress abstracts were excluded from the evidence synthesis.

Data Extraction
Data extraction was performed by one author (PM), with another independent extraction by one of two other authors (GC and AC). Any disagreements were resolved by discussion and consensus. The following data were extracted using predefined cells: first author, publication date, country, screening interval, ethnicity, number of identified BRCA1 and BRCA2 variants, and number of tested PCa.

Data Analysis
For each study, we first estimated the prevalence of BRCA1/2 variants in PCa from the published reports. We calculated 95% confidence intervals (CIs) using the Clopper-Pearson Exact binomial method. For the meta-analysis, we used random-effects models, with maximum likelihood estimates and the Freeman-Tukey double arcsine transform method to stabilize variances. Heterogeneity between studies was assessed using the Cochran Q test. The percentage of total variation across studies due to heterogeneity was evaluated by the I2 measure. We produced forest plots including the study specifics and the overall prevalence estimates. Probability of publication bias was assessed using funnel plots with the Begg's test. Statistical analyses were performed using the R package meta. All p-values were two-sided.

Study Features
We selected 35 original studies published from 1996 to 2021. These reported data were collected from 1983 to 2017. A total of 27,252 PCas were screened for BRCA1 and 24,633 for BRCA2. Three studies comprised heterogeneous populations [13][14][15], and eleven studies included Ashkenazi PCa patients for BRCA screening (Table 1).

Prevalence of BRCA1/2 Mutations
We identified 46 BRCA1 and 68 BRCA2 variants in PCa Ashkenazi patients, and 108 BRCA1 and 402 BRCA2 variants in non-Ashkenazi patients. Regarding the classic founder BRCA1/2 variants in Ashkenazi patients, we identified 185delAG in thirty-nine, 5382insC in seven, and 6176delT in sixty-eight patients, respectively. Considering the overall PCa patients, in Ashkenazi patients we identified a total of 46 (40. Studies from non-Ashkenazi populations had a significant heterogeneity in BRCA1 and BRCA2 groups (p < 0.01), both (Figures 1 and 2).
In Supplementary Table S1, we described the pathogenic classification of the germline BRCA1/2 variants reported in the respective original studies. When a variant's nomenclature was available in the text, we revised the pathogenic role of these alterations according to the most recent ClinVar classification (Supplementary Table S2).    Studies from non-Ashkenazi populations had a significant heterogeneity in BRCA1 and BRCA2 groups (p < 0.01), both (Figures 1 and 2).
In Supplementary Table S1, we described the pathogenic classification of the germline BRCA1/2 variants reported in the respective original studies. When a variant's nomenclature was available in the text, we revised the pathogenic role of these alterations according to the most recent ClinVar classification (Supplementary Table S2).
Test for subgroup differences:

Risk of Bias
Examination of the funnel plot revealed no evidence of publication bias (p = 0.22 and p = 0.39, respectively, for BRCA1 and BRCA2 by Begg's test) (Figure 4).

Risk of Bias
Examination of the funnel plot revealed no evidence of publication bias (p = 0.22 and p = 0.39, respectively, for BRCA1 and BRCA2 by Begg's test) (Figure 4).

Hereditary PCa in Ashkenazi Is Associated with Germline BRCA Mutation Status
This study presents a different distribution of germline BRCA1/2 variants among PCa Ashkenazi and non-Ashkenazi patients. We identified a higher prevalence of germline BRCA1 variants in Ashkenazi Jewish patients in comparison to the non-Ashkenazi population, while no significant difference of the prevalence of germline BRCA2 variants was observed between the two populations.
Some ethnicities present a specific relation with founder germline gene variants. Significant associations were found in Māori kindred carrying CDH1 germline pathogenic variants for gastric cancer risk, as well as in Ashkenazy Jewish and Hakka Chinese populations with BRCA variants for BC risk [48].
With reference to the BRCA gene and Ashkenazi patients, there is a documented relation with BC risk. The 185delAG and 5382insC variants in BRCA1 and the 6174delT variant in BRCA2 were detected in a high proportion of Ashkenazi Jewish women with a diagnosis of BC. Initially, the 185delAG variant was found in 17%, 5382insC in 2%, and 6174delT in 6% of cases [49]. These three founder variants account for the vast majority (~96%) of BRCA1/2 variants in women of Ashkenazi Jewish descent [50]. Specifically, a national Israeli study of 111 Ashkenazi families showed that among families in which the BRCA1 185delAG variant was detected, 20.2% of the women had BC. A similar incidence of 24.1% was found among women from families with the BRCA2 6174delT variant. Among families carrying the BRCA1 5382insC variant, the incidence was appreciated higher (39.4%) [12]. We noted a different prevalence of founder variants in PCa Ashkenazi patients. In our study we identified a total of 114 founder germline BRCA1/2 variants in Ashkenazi patients. In detail, the most frequent variants were 6174delT (59.7%), 185delAG

Hereditary PCa in Ashkenazi Is Associated with Germline BRCA Mutation Status
This study presents a different distribution of germline BRCA1/2 variants among PCa Ashkenazi and non-Ashkenazi patients. We identified a higher prevalence of germline BRCA1 variants in Ashkenazi Jewish patients in comparison to the non-Ashkenazi population, while no significant difference of the prevalence of germline BRCA2 variants was observed between the two populations.
Some ethnicities present a specific relation with founder germline gene variants. Significant associations were found in Māori kindred carrying CDH1 germline pathogenic variants for gastric cancer risk, as well as in Ashkenazy Jewish and Hakka Chinese populations with BRCA variants for BC risk [48].
With reference to the BRCA gene and Ashkenazi patients, there is a documented relation with BC risk. The 185delAG and 5382insC variants in BRCA1 and the 6174delT variant in BRCA2 were detected in a high proportion of Ashkenazi Jewish women with a diagnosis of BC. Initially, the 185delAG variant was found in 17%, 5382insC in 2%, and 6174delT in 6% of cases [49]. These three founder variants account for the vast majority (~96%) of BRCA1/2 variants in women of Ashkenazi Jewish descent [50]. Specifically, a national Israeli study of 111 Ashkenazi families showed that among families in which the BRCA1 185delAG variant was detected, 20.2% of the women had BC. A similar incidence of 24.1% was found among women from families with the BRCA2 6174delT variant. Among families carrying the BRCA1 5382insC variant, the incidence was appreciated higher (39.4%) [12]. We noted a different prevalence of founder variants in PCa Ashkenazi patients. In our study we identified a total of 114 founder germline BRCA1/2 variants in Ashkenazi patients. In detail, the most frequent variants were 6174delT (59.7%), 185delAG (34.2%), and 5382insC (6.1%), respectively. In comparison to BC, the founder 6174delT (BRCA2) and 185delAG (BRCA1) variants were more prevalent in PCa.

Further Indications for PC Genetic Screening
The National Comprehensive Cancer Network (NCCN) recommends a BRCA2 genetic test starting at age 40 years in cases of a personal history of metastatic, node-positive, biochemically recurrent, Gleason ≥8, or Gleason 7 disease with a strong family history of BRCA-related cancers. Additional men with PCa were referred if their personal and/or family history was suspicious for hereditary cancer predisposition, such as Lynch Syndrome [56]. However, BRCA1 is not routinely included in PCa genetic screening but only "considered", due to the lower prevalence in men with PCa. Our results demonstrate a similar prevalence of BRCA1 and BRCA2 in PCa Ashkenazi Jewish patients. This suggests "recommending" both genes in their genetic testing to inform decision-making for active surveillance.

Limitations
The germline BRCA1/2 variant frequency could be affected by research activity, publication bias or access to medical care, and some data could be not retrievable from MEDLINE. However, we assume that this potential bias is very low. Data collection was performed independently by two authors.
We were not able to quantify the real PCa risk in BRCA1 and BRCA2 due to the lack of information about healthy carriers. However, our first aim was to assess only the prevalence of BRCA variants between two different populations.
Some studies reported in this systematic review performed genetic screening in Ashkenazi Jewish patients only considering the BRCA1/2 "hotspot" points such as 185delAG, 5382insC, 6174delT, and not all the entire coding regions. We can consider this approach as a "safe procedure" because founder variants are classically identified at a higher (significant) frequency in these populations.
We collected all germline BRCA variants reported in these studies. Some of these studies did not specify if these variants are variants of unknown significance (VUS) or pathogenetic [22,25,28,37,[39][40][41]46], as they reported only the overall number of identified mutations; other studies [31,34,38] included both VUS and pathogenetic germline BRCA variants. To provide additional information for further studies, when variants' nomenclature was available in the original study, we have revised these alterations in accord with the most recent ClinVar classification.

Conclusions
Ashkenazi Jewish ancestry was associated with BRCA1/2 variants in men with PCa, with a prevalence of BRCA2 (1-3%) [20,26,30]. This meta-analysis suggests that BRCA1 and BRCA2 occur in PCa Ashkenazi with a similar prevalence; moreover, the prevalence of germline founder variants presents a different frequency in PCa in comparison to BC, in particular with 6176delT (BRCA2) and 185delAG (BRCA1) variants. This should be considered for active surveillance in Ashkenazi men.