Biallelic Inactivation Of BRCA2 Research Articles

A glycolytic metabolite bypasses “two-hit” tumor suppression by BRCA2

Knudson's "two-hit" paradigm posits that carcinogenesis requires inactivation of both copies of an autosomal tumor suppressor gene. Here, we report that the glycolytic metabolite methylglyoxal (MGO) transiently bypasses Knudson's paradigm by inactivating the breast cancer suppressor protein BRCA2 to elicit a cancer-associated, mutational single-base substitution (SBS) signature in nonmalignant mammary cells or patient-derived organoids. Germline monoallelic BRCA2 mutations predispose to these changes. An analogous SBS signature, again without biallelic BRCA2 inactivation, accompanies MGO accumulation and DNA damage in Kras-driven, Brca2-mutant murine pancreatic cancers and human breast cancers. MGO triggers BRCA2 proteolysis, temporarily disabling BRCA2's tumor suppressive functions in DNA repair and replication, causing functional haploinsufficiency. Intermittent MGO exposure incites episodic SBS mutations without permanent BRCA2 inactivation. Thus, a metabolic mechanism wherein MGO-induced BRCA2 haploinsufficiency transiently bypasses Knudson's two-hit requirement could link glycolysis activation by oncogenes, metabolic disorders, or dietary challenges to mutational signatures implicated in cancer evolution.

Abstract C074: Clinico-genomic characterization of N=2,460 pancreatic adenocarcinoma identifies KRASMUT dosage as prognostic of overall survival across disease stages

Abstract Background: The majority (~80%) of patients (pts) with pancreatic adenocarcinomas (PDAC) present with advanced disease. Most sequencing efforts to date have focused on early stage disease. Herein, we leverage a large clinical sequencing cohort of N= 2460 pts with PDAC to characterize the clinico-genomic landscape across different disease stages. Methods: Tumors from 2460 pts were sequenced using MSK-IMPACT clinical sequencing assay and mutations called via CLIA-approved pipelines. Detailed clinical descriptors including lines of treatment and response were abstracted for N=1451 (59%) pts. Intratumor heterogeneity estimates including allele-specific copy number were inferred using FACETS. Results: Of N=2460, at diagnosis 34% of pts had resectable tumors, and 24% and 42% had locally advanced and metastatic disease, respectively. 94% of pts had KRASMUT tumors. Expectedly, MAPK pathway alterations were significantly enriched in KRASWT tumors (60% vs. 7% in KRASMUT, p < 0.001) with gain-of-function kinase oncogene fusions exclusively observed in these tumors (p<0.001). In addition, GNAS, PTEN, FOXP1, SMARCB1 and CREBBP were enriched in the KRASWT tumors (q < 0.05). Collectively, pts with KRASWT/MAPK MUT and KRASWT/MAPK WT tumors comprise 4% and 2% of all pts PDAC, respectively. Germline pathogenic variants in high/moderate penetrance genes were more common in pts with KRASWT tumors compared to pts with KRASMUT tumors (20% vs. 10%, p < 0.001). Pathogenic germline alterations in BRCA1/2 and PALB2 were observed in 6% (N=144) of cohort. Biallelic inactivation of BRCA2 specifically was associated with prolonged response of metastatic pts to PARP-inhibitor maintenance therapy with 10.3 months on treatment prior to progression compared to 3.4 months for those with biallelic inactivation of other HRD genes and 2.2 months for those with non-biallelic inactivation. Among KRASMUT tumors assessed for KRAS copy-number allelic imbalance (AI) (N=1097), 41% (N=452) had AI at the KRAS locus with mutant-allele selected for in 94% of tumors with imbalance. Among KRASMUT tumors with normal genome ploidy, overall, 20% had a mutant allele gain ranging from 10% in resectable to 29% of metastatic tumors. We observe significantly lower OS among pts with KRASMUT dosage gain compared to heterozygous KRASMUT across pts with resectable (HR: 0.66, 95% CI: 0.18-1.15, p<0.01) and metastatic (HR: 0.39, 95% CI: 0.16-0.63, p=0.001) diseases with statistical significance not reached among the locally advanced disease (HR: 0.4, 95% CI: -0.01-0.81, p=0.056). Notably, the OS of pts with loss of the wild-type allele and no mutant copy gain was indistinguishable from that of heterozygous KRASMUT tumors (HR: -0.11, 95% CI: -0.37-0.15, p=0.4). Conclusion: In this large cohort of 2460 pts with PDAC, we observed that KRASMUT dosage gain is a significant negative predictor of OS. These findings highlight the importance of incorporating allelic-dosage into comprehensive molecular testing in PDAC given prognostic importance and the emerging era of direct RAS targeting. Citation Format: Anna M. Varghese, Maria A. Perry, Daniel Muldoon, Subhiksha Nandakumar, Amanda Erakky, Bastien Nguyen, Amanda Zucker, Hulya Sahin Ozkan, Olca Basturk, Debyani Chakravarty, David P. Kelsen, Wungki Park, Kenneth H. Yu, Alice C. Wei, Nikolaus Schultz, Michael F. Berger, Christine Iacobuzio-Donahue, Chaitanya Bandlamudi, Eileen M. O'Reilly. Clinico-genomic characterization of N=2,460 pancreatic adenocarcinoma identifies KRASMUT dosage as prognostic of overall survival across disease stages [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Pancreatic Cancer; 2023 Sep 27-30; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(2 Suppl):Abstract nr C074.

Final results of a pilot study of docetaxel and carboplatin for treatment of patients with mCRPC containing biallelic inactivation of genes in the homologous recombination DNA repair pathway.

5054 Background: Inactivating mutations in genes important in homologous recombination DNA repair (HRD) are present in the tumors of ~25% of patients with metastatic castration resistant prostate cancer (mCRPC). These alterations are associated with more aggressive disease but may also predict vulnerability to DNA damaging agents. We previously reported promising interim results from a single arm, Phase 1/2 trial studying the combination of the DNA damaging agent carboplatin with docetaxel for patients with mCRPC containing HRD mutations. Here we report final results after completing accrual and two additional years of follow up. Methods: We assessed response to the combination of docetaxel 60mg/m2 and carboplatin AUC 5 IV q21 days in patients with mCRPC whose tumors had evidence of biallelic inactivation of genes involved in HRD and who had progressed on any prior treatment, including docetaxel and/or PARP inhibitor (PARPi). The primary endpoint was the proportion of patients who achieved ≥50% PSA decline from baseline (PSA50). With H0 of PSA50 of 26%, 14 patients provided 80% power to conclude H1 of PSA50 of 60% based on Simon's 2-stage design with 1-sided α = 5%. The secondary endpoints included PSA30, response duration, progression-free survival (PFS), and overall survival (OS). Results: The trial opened in Jan 2016 and completed in Sep 2021. A total of 16 patients were treated on study, including 6 who had previously received PARPi and 5 who had received docetaxel. 11/16 patients (69%) achieved PSA50. 7/9 patients (78%) with biallelic inactivation of BRCA2 (7), BRCA1 (1), or PALB2 (1) achieved PSA50. Other biallelic inactivated HRD-related genes were ATM (1), CHD1 (1), CDK12 (3), MRE11A (1), and NBN (1). Of these patients, 4/7 (57%) achieved PSA50. Notably, 3/6 patients (50%) previously treated with PARPi therapy achieved PSA50. The median PFS was 8.4 months, and the median OS was 2 years. 6/16 patients (38%) had grade 3 AEs, most commonly thrombocytopenia (25%) and anemia (13%). One patient (6%) had a grade 4 AE (thrombocytopenia). Conclusions: The addition of carboplatin to docetaxel significantly improved response rates in patients with mCRPC with biallelic inactivation in genes involved in the HRD pathway. Responses were also seen in patients who had previously received PARPi. The combination was relatively safe and well-tolerated. The encouraging activity and favorable toxicity profile observed here merits further investigation. Additional work is ongoing to further refine biomarkers predictive of treatment response and resistance. Clinical trial information: NCT02598895 .

Abstract 5465: HRDetect as a predictive score of platinum response in advanced PDAC

Abstract Background: Predictors of response to DNA damaging agents may expand the population of patients who could benefit from platinum and/or PARP inhibition in pancreatic cancer (PDAC). The HRDetect score derived from whole genome sequencing (WGS) incorporates patterns of substitution base signatures and structural variation and is associated with tumours deficient in homologous recombination repair (HRD). Methods: The prospective COMPASS trial (NCT 02750657) enrolls patients with advanced PDAC prior to systemic treatment for WGS and RNAseq. Choice of combination chemotherapy is at the discretion of the physician. HRD tumours are identified by the presence of a number of known genomic characteristics including evidence of biallelic inactivation of BRCA/PALB2 or the RAD51 family of genes, the presence of signature 3, the number and proportion of indels that are deletions of at least 4 base pairs (bp), and the presence of rearrangement signatures 3 and 5. We ascertained the number of patients with high HRDetect scores (>0.7) and evaluated outcomes and response to chemotherapy including platinum regimens. Results: As of 1st May 2019 204 eligible patients were enrolled. High HRDetect scores (HRDetecthi ) were present in 26/204 (13%). Only half of these cases were represented by HRD tumours including: 9 germline BRCA1/2 or PALB2 cases with biallelic inactivation and 3 tumours with somatic biallelic inactivation of BRCA2, RAD51C and XRCC2. 1 additional HRD case was of unknown aetiology. All HRD cases were HRDetecthi. Two germline carriers of BRCA2 without a second somatic hit were HR intact with low HRDetect scores. Of the remaining 13 non-HRD tumours identified as HRDetecthi, 6 exhibited a tandem duplicator phenotype (TDP) with tandem duplications ranging from 10Kbp to 1Mbp in size. These tumours did not have any other genomic characteristics of HRD. Notably, of the 204 patients included in this analysis, a TDP was present in 15 (7%), of which 40% were HRDetecthi. In patients treated with modified FOLFIRINOX(mFFX) (n=111, *includes 2 patients treated with cisplatin/gemcitabine) the response rate in HRDetecthi patients (n=16) was 56% vs 20% in HRDetectlo patients (n=95) p=0.005. There was no difference in response rates according to HRDetect score in patients treated with gemcitabine-nab-paclitaxel; HRDetecthi (n=7) 14.3% vs. HRDetectlo(n=71) 32.8%, p=0.42. Median OS in all patients receiving mFFX (n=111) was 10.2 months; in patients with HRDetecthi PDAC, median OS was 15.5 mths vs. 9.9 mths in HRDetectlo PDAC, (HR 0.42, 95% CI 0.24-0.87, p=0.01). In all patients (n=78) receiving gemcitabine based combination treatment the median OS was 8.1 mths; in HRDetecthi patients median OS was 11.5mths vs 7.8 mths in HRDetectlo patients (HR 0.94, 95% CI 0.42-2.13, p=0.8). Conclusions: In patients with advanced PDAC with high HRDetect scores, response rate to FFX is over 50% and survival is significantly longer compared to patients with PDAC and low HRDetect scores. HRDetect identifies an additional population of patients with non-HRD PDAC who benefit from DNA damaging agents. Citation Format: Grainne M. O'Kane, Robert E. Denroche, Amy Zhang, Sarah Picardo, Robert C. Grant, MIchael J. Allen, Gun Ho Jang, Yifan Wang, Anna Dodd, Stephanie Rampotar, Shawn Hutchinson, Mustaphe Tehfe, James J. Biagi, Dianne Chadwick, Bernard Lam, Julie Wilson, Faiyaz Notta, Sandra E. Fischer, George Zogopoulos, Steven Gallinger, Jennifer J. Knox. HRDetect as a predictive score of platinum response in advanced PDAC [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5465.

A pilot study of docetaxel and carboplatin for treatment of patients with mCRPC containing biallelic inactivation of genes in the BRCA1/2 pathway.

127 Background: Despite new treatments, metastatic castration resistant prostate cancer (mCRPC) remains ultimately lethal. Upwards of 25% of mCRPC tumors have alterations in homologous recombination DNA repair (HRD) genes, most frequently BRCA2. Retrospective data suggest addition of the DNA damaging agent carboplatin to standard docetaxel for patients with mCRPC whose tumors have biallelic inactivation of BRCA2 may be effective. Methods: In this prospective, pilot single-arm phase 2 study, we assess response to the combination of docetaxel 60mg/m2 and carboplatin AUC 5 IV q21 days in patients with mCRPC whose tumors have evidence of biallelic inactivation of BRCA1, BRCA2 or ATM and have progressed after any prior treatment, including prior docetaxel and/or PARP inhibitor (PARPi). The primary endpoint is rate of ≥50% PSA decline from baseline (PSA50). With H0 of PSA50 of 26%, 14 patients will provide 80% power to conclude H1 of PSA50 of 60% based on Simon's 2-stage design with 1-sided α = 5%. Secondary endpoints include PSA30, response duration, time to progression and correlative studies. Biallelic inactivation of other HRD-related genes were included at investigators’ discretion. Results: The study opened in Jan 2016 and has enrolled 8/14 (57%) of patients plus 5 patients with other HRD-related genes. 6/13 (46%) treated pts had grade 3 expected AEs, and no grade 4-5 AEs were observed. To date, 7/8 (88%) of pts with biallelic inactivation of BRCA1, BRCA2 and ATM (Table) and 10/13 (77%) of all pts achieved a PSA50 (other HRD-related genes include CDK12, CHD1, MRE11A and PALB2). Updated results will be reported at final presentation. Conclusions: Addition of carboplatin to docetaxel appears to be well-tolerated and effective for patients with mCRPC whose tumors have biallelic inactivation in selected HRD genes such as BRCA2, including those with prior treatment with PARP inhibitor. Clinical trial information: NCT02598895. [Table: see text]

Germline BLM mutations and metastatic prostate cancer.

Biallelic loss-of-function BLM mutations result in Bloom syndrome: a genetic disorder characterized by growth deficiencies, photosensitivity, and multiple cancer susceptibilities. There are conflicting reports about whether or not heterozygous BLM carriers are at a higher risk of various cancers. Without BLM protein functionality, there is evidence of increased sister chromatid exchange and chromosomal instability. Metastatic prostate cancer patients (N = 796) underwent germline genetic testing as part of routine care at three academic centers. Patients with heterozygous BLM mutations were identified. Tumor tissue was analyzed for somatic alterations in those patients who had a germline pathogenic mutation. Control data using a population sample were extracted from the Genome Aggregation Database. Heterozygous BLM germline mutations in 5 of 796 patients (prevalence, 0.63%). All mutations were loss-of-function truncating alterations. None of the mutations were BLMAsh . The control population (gnomAD) frequency of pathogenic or likely pathogenic BLM mutations was 0.18% (212 of 116 653). The relative risk (RR) of BLM mutations in metastatic prostate cancer patients was 3.4 (95% CI, 1.42-8.33; P < .0062) compared to gnomAD controls. Tumor DNA sequencing in the BLM carriers showed no evidence of somatic BLM mutations. Interestingly, 3 of 5 BLM germline carriers had bi-allelic BRCA2 inactivation evident on tumor sequencing. One patient had both germline and somatic mutations in BRCA2. Excluding the patient with the germline BRCA2 mutation (BLM prevalence, 4 of 796: 0.50%) still yielded a statistically significant finding vs the gnomAD controls (RR, 2.8; 95% CI, 1.02-7.39; P < .04). Truncating BLM germline mutations occur at a higher frequency in patients with advanced prostate cancer as compared to control populations. Though no biallelic loss of BLM was no noted in cancers, a surprising number of the BLM germline heterozygotes had pathogenic BRCA2 mutations in their tumor.

Germline heterozygous BLM mutations and prostate cancer risk.

321 Background: The BLM gene encodes a RecQ DNA helicase that is involved in homologous recombination. Biallelic BLM inactivation leads to Bloom syndrome, an inherited genetic disorder marked by chromosomal instability and multiple cancer susceptibilities. Conflicting studies have suggested that heterozygous BLM mutation carriers may have an increased risk of various cancers. Here we explored the role of germline pathogenic BLM mutations in prostate cancer. Methods: Prostate cancer patients with heterozygous BLM mutations were assembled from Tulane Cancer Center (TCC), Johns Hopkins Hospital (JHH) and University of Washington (UW). BLM germline mutations were identified either through commercial germline testing (Invitae), the UW-BROCA panel, or whole-exome sequencing. Corresponding tumor tissue was analyzed by DNA sequencing for somatic alterations. Population level control data were obtained from the Genome Aggregation Database (gnomAD). Results: 6 BLM germline carriers were identified among 985 advanced prostate cancer case; 2/295 TCC patients, 2/172 JHH patients, and 2/518 UW patients. Overall, pathogenic BLM mutations were detected in 0.609% (6/985) of prostate cancer cases. All mutations were loss-of-function truncating lesions (splicing or nonsense alterations). No Ashkenazi BLM mutations were observed. The population frequency of pathogenic or likely pathogenic BLM alterations detected in gnomAD was 0.025% (31/124,589). Compared to gnomAD controls, the relative risk of BLM mutations in prostate cancer patients was 24.3 (95% CI 10.2 to 58.2; P &lt; 0.0001). One family had a pathogenic splice variant in BLM that cosegregated with disease in three of three cases with lethal/high risk prostate cancer. Tumor DNA sequencing was possible in 5 of 6 BLM carriers; no case demonstrated LOH or additional somatic BLM mutations. Interestingly, 2/5 cases on tumor sequencing also had bi-allelic BRCA2 inactivation. Conclusions: Germline BLM mutations may play a role in prostate cancer risk. Given the role of BLM in chromosomal stability and evidence of concurrent BRCA2 inactivation in a subset of cases, larger cohorts and functional analyses will be critical for better understanding the role of BLM in prostate cancer.

Abstract 2476: Preclinical assessment of the PARP inhibitor rucaparib in homologous recombination deficient prostate cancer models

Abstract Rucaparib (CO-338) is an oral small molecule inhibitor of the poly(ADP-ribose) polymerase (PARP) enzymes PARP-1, PARP-2 and PARP-3 that is being developed for cancer patients with evidence of homologous recombination (HR) deficiency, including BRCA1 and BRCA2 mutations. PARP inhibitors have demonstrated clinical activity in BRCA1, BRCA2, and ATM mutant prostate cancer patients (Mateo et al. N Engl J Med. 2015;373:1697-708); however, limited preclinical validation of PARP inhibitors in prostate cancer has been reported to date, since no BRCA mutant nor HR deficient prostate cell lines have been identified. In this study, we modelled the functional inactivation of DNA repair genes using siRNA and CRISPR/Cas9, and examined the impact on PARP inhibition, in the DU145 and PC-3 prostate cancer cell lines. These cell lines were chosen based on transfection efficiency, lack of obvious genetic defects in DNA repair pathways, and baseline insensitivity to rucaparib (IC50 &amp;gt; 10 µM). A panel of 26 DNA repair genes were individually knocked down by siRNA, and changes to rucaparib potency were examined in a 7-day cell viability assay. The knockdown of BRCA1 or BRCA2 increased rucaparib cytotoxicity in both prostate cell lines. For example, the IC50 of rucaparib in DU145 and PC-3 cells with reduced BRCA2 levels was 275 and 297 nM, representing a 36- and 37-fold increase in rucaparib sensitivity, respectively. In addition to BRCA1 and BRCA2, the knockdown of several other genes including BARD1, CDK12, FANCA, PALB2, RAD51, RAD51C, RAD51D, and RAD54L increased rucaparib efficacy ≥ 2-fold in at least 1 cell line examined. To further investigate HR deficiency in prostate cancer, BRCA2 was knocked out in the human 22Rv1 prostate cancer cell line using CRISPR/Cas9. Clone 1-50 displayed biallelic BRCA2 inactivation due to the introduction of a deleterious premature stop codon, and immunoblot analysis verified lack of the full-length BRCA2 protein. The IC50 of rucaparib in the parental and clone 1-50 cells was 9,504 and 287 nM, respectively, demonstrating a 33-fold increase in rucaparib cytotoxicity in this BRCA2 deficient model. Androgen receptor (AR) signaling and proliferation were also examined in clone 1-50. In contrast to published reports (Schiewer et al. Cancer Discov. 2012;2:1134-49), no impact of PARP inhibition on dihydrotestosterone (DHT) induced gene expression was observed in the parental 22Rv1 and BRCA2 deficient clone 1-50 cell lines. In vivo model development and efficacy studies with the 22Rv1 and clone 1-50 cell lines are ongoing. Taken together, these findings support the hypothesis that deficiencies in BRCA1 and BRCA2, as well as additional HR genes, may sensitize prostate cancer cells to rucaparib. A phase 2 study investigating rucaparib in patients with metastatic castration-resistant prostate cancer and HR gene deficiency (TRITON2) is ongoing (NCT02952534). Citation Format: Minh Nguyen, Andrew D. Simmons, Thomas C. Harding. Preclinical assessment of the PARP inhibitor rucaparib in homologous recombination deficient prostate cancer models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2476. doi:10.1158/1538-7445.AM2017-2476

Commentary on “Biallelic inactivation of BRCA2 in platinum-sensitive metastatic castration-resistant prostate cancer”. Cheng HH, Pritchard CC, Boyd T, Nelson PS, Montgomery B. Eur Urol. Jun 2016;69(6):992–5.

Understanding the molecular underpinnings of sensitivity to specific therapies will advance the goal of precision medicine in prostate cancer (PCa). We identified 3 patients with metastatic castration-resistant PCa (mCRPC) who achieved an exceptional response to platinum chemotherapy (not first-line treatment for PCa), despite disease progression on prior standard therapies. Using targeted next-generation sequencing on the primary and metastatic tumors, we found that all 3 patients had biallelic inactivation of BRCA2, a tumor suppressor gene critical for homologous DNA repair. Notably, 2 had germline BRCA2 mutations, including a patient without compelling family history who was diagnosed at age 66 year. The third patient had somatic BRCA2 homozygous copy loss. Biallelic BRCA2 inactivation in mCRPC warrants further exploration as a predictive biomarker for sensitivity to platinum chemotherapy.

Abstract S2-02: The landscape of somatic genetic alterations in BRCA1 and BRCA2 breast cancers

Abstract Introduction: Women carrying BRCA1 or BRCA2 germline mutations have a 45-80% lifetime risk of developing breast cancer (BC). BRCA1 and BRCA2 are perceived as bona fide tumor suppressor genes, whereby bi-allelic inactivation in tumor cells is required for tumorigenesis. Recent studies have indicated that loss of heterozygosity (LOH) of the wild-type allele of BRCA1 may be heterogeneous and constitute a late event. Therefore, additional somatic events prior to full BRCA1/2 inactivation may be required for tumorigenesis. Given that the somatic events that result in the development of BRCA1/2-BCs and their chronology are not understood, here we sought to define the genomic landscape of BRCA1/2-BCs and whether LOH of BRCA1/2 wild-type allele and/or mutations affecting additional tumor suppressor genes would be clonal or subclonal in these cancers. Methods: We retrieved 29 BRCA1-BCs and 10 BRCA2-BCs from the Pathology Departments of the authors' institutions. DNA extracted from microdissected tumor and normal breast samples was subjected to targeted capture massively parallel sequencing using either the MSK-IMPACT assay or an assay targeting all exons of 254 genes recurrently mutated in BC or related to DNA repair. Somatic single nucleotide variants, small insertions and deletions and copy number alterations affecting genes present in both sequencing assays (111 genes) were defined using state-of-the-art bioinformatics algorithms. ABSOLUTE and FACETS were employed to define clonal (i.e. present virtually in 100% of the cancer cells of a given case) and subclonal mutations and the presence of LOH of the BRCA1 and BRCA2 wild-type alleles. Results: Our analysis revealed bi-allelic inactivation of BRCA1 in 28 of 29 BRCA1-BCs (93% harbored LOH of the BRCA1 wild-type allele and 3% harbored a second somatic BRCA1 pathogenic mutation). The only BRCA1-BC lacking bi-allelic inactivation of BRCA1 was an estrogen receptor-positive lobular carcinoma, lacking genomic features consistent with homologous recombination DNA repair defects, diagnosed at 62 years of age. Bi-allelic inactivation of BRCA2 was found in all cases (100% of harbored LOH of the BRCA2 wild-type allele). A clonal somatic 'second hit' resulting in bi-allelic inactivation of BRCA1 or BRCA2 was detected in 76% and 100% of BRCA1-BCs and BRCA2-BCs, respectively. In BRCA1-BCs, TP53 mutations were detected in 76% of cases, and these mutations were found to be clonal in 58% of cases. The repertoire of somatic mutations affecting BRCA1-BCs included clonal somatic mutations or homozygous deletions of known tumor suppressor genes, such as PTEN, RB1, CDKN2A and NF1. In contrast, only 10% of the BRCA2-BCs harbored TP53 somatic mutations. Though clonal somatic mutations in several cancer genes were detected, 40% of BRCA2-BCs had no mutations affecting the cancer genes analyzed. Conclusions: Bi-allelic inactivation of BRCA1 and BRCA2 are frequent events in BRCA1-BCs and BRCA2-BCs, respectively. In a subset of BRCA1-BCs, however, the second 'hit' appeared to be subclonal, whereas mutations affecting TP53 and other tumor suppressor genes were clonal, supporting the notion that at least in a subset of these tumors, loss of the wild-type allele of BRCA1 may be preceded by inactivation of another tumor suppressor gene. Citation Format: Geyer FC, Burke KA, Macedo GS, Piscuoglio S, Ng CK, Martelotto LG, Papanastatiou AD, De Filippo MR, Schultheis AM, Brogi E, Robson M, Wen YH, Weigelt B, Schnitt SJ, Tung N, Reis-Filho JS. The landscape of somatic genetic alterations in BRCA1 and BRCA2 breast cancers [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr S2-02.

Biallelic inactivation of BRCA2 in metastatic castration-resistant prostate cancer and platinum sensitivity.

164 Background: Predictive biomarkers are urgently needed in the treatment of metastatic castration-resistant prostate cancer (mCRPC), and the promise of precision medicine depends on understanding the molecular underpinnings of sensitivity to specific therapies. Methods: We identified three patients with mCRPC who achieved exceptional response to platinum chemotherapy after failing prior standard therapies. To identify associated molecular lesions, we retrospectively performed clinical targeted next generation sequencing (UW-OncoPlex) on metastatic and/or primary tumors. Results: Three of three patients were identified to have biallelic inactivation of BRCA2 (breast cancer 2, early onset), a tumor suppressor gene critical for homologous DNA repair and mutations of which are associated with hereditary breast and ovarian cancers. Two patients were subsequently confirmed to carry deleterious germline mutations in BRCA2, including one patient who was diagnosed at age 66 and lacked a significant family history of cancer. The third patient had somatic BRCA2 homozygous copy loss. Conclusions: Biallelic BRCA2 inactivation in mCRPC warrants further study as a predictive biomarker for sensitivity to platinum chemotherapy.

Germline Brca2 Heterozygosity Promotes Kras G12D -Driven Carcinogenesis in a Murine Model of Familial Pancreatic Cancer

Inherited heterozygous BRCA2 mutations predispose carriers to tissue-specific cancers, but somatic deletion of the wild-type allele is considered essential for carcinogenesis. We find in a murine model of familial pancreatic cancer that germline heterozygosity for a pathogenic Brca2 truncation suffices to promote pancreatic ductal adenocarcinomas (PDACs) driven by Kras(G12D), irrespective of Trp53 status. Unexpectedly, tumor cells retain a functional Brca2 allele. Correspondingly, three out of four PDACs from patients inheriting BRCA2(999del5) did not exhibit loss-of-heterozygosity (LOH). Three tumors from these patients displaying LOH were acinar carcinomas, which also developed only in mice with biallelic Brca2 inactivation. We suggest a revised model for tumor suppression by BRCA2 with implications for the therapeutic strategy targeting BRCA2 mutant cancer cells.

Fanconi anemia and biallelic BRCA2 mutation diagnosed in a young child with an embryonal CNS tumor

Medulloblastoma, the most common pediatric malignant brain tumor often arises sporadically; however, in a subgroup of patients, there exist familial conditions such as Fanconi anemia with biallelic BRCA2 mutation that predispose patients to developing medulloblastoma. Biallelic inactivation of BRCA2 in Fanconi anemia has been previously described in only 11 patients with medulloblastoma in the literature to date. Here we report two siblings diagnosed with central nervous system embryonal tumors at an early age in association with biallelic BRCA2 inactivation, including the first reported case of a spinal cord primitive neuroectodermal tumor (PNET) in a BRCA2/FANCD1 kindred.

Mixed Ovarian Germ Cell Tumor in a BRCA2 Mutation Carrier

BRCA2 germ-line mutations confer an increased risk of developing breast and ovarian cancer. We report the occurrence of a mixed ovarian germ cell tumor (GCT) (50% embryonal carcinoma, 20%-25% choriocarcinoma, 10%-15% dysgerminoma, and 10%-15% immature teratoma) in a 33-year-old Ashkenazi Jewish woman, carrier of the BRCA2:6174delT mutation. The mutation is also present in the patient's father, who was diagnosed with breast cancer at age 59 and with prostate cancer at age 69. This is the first report of a GCT in a BRCA2 mutation carrier; there was one previous report of an ovarian dysgerminoma in a BRCA1 carrier. Molecular analysis of the proband's tumor DNA revealed there was no loss of heterozygosity of the wild-type allele in the tumor, as is usually the case for epithelial BRCA-related ovarian tumors. This suggests either that biallelic inactivation of BRCA2 is not required for GCT development or that this is a chance event unrelated to the presence of the mutation.

Lower level of BRCA2 protein in heterozygous mutation carriers is correlated with an increase in DNA double strand breaks and an impaired DSB repair

The BRCA2 protein is involved in the maintenance of genomic stability through its key role in homologous recombination repair of DNA double strand breaks. Biallelic inactivation of BRCA2 leads to a defect in DNA repair and is associated with a chromosomal instability phenotype. Recent studies on familial breast cancer clusters revealed chromosomal rearrangements and higher rates of sister chromatid exchanges also in heterozygous BRCA2 mutation carriers. In the present study, lymphoblastoid cell lines of heterozygous BRCA2 mutation carriers and of wildtype relatives were compared with regard to BRCA2 mRNA and protein expression and capacity to repair DNA damage induced by γ-irradiation and mitomycin C. BRCA2+/− cells showed lower amounts of the full-length BRCA2 protein compared to BRCA2+/+ cells. The kinetics of γ-H2AX protein level revealed distinct defects in DNA double strand break repair in the BRCA2+/− cells. These results are indicative of a haploinsufficiency phenotype in BRCA2+/− cells, suggesting that reduced amounts of functional BRCA2 protein in BRCA2+/− carriers are insufficient for an efficient repair of DNA double strand breaks, a condition that could contribute to the impairment of genomic stability.

Biallelic inactivation of BRCA2 in Fanconi anemia Howlet NG et al. (2002) Science 297: 606–609

Clinical GeneticsVolume 63, Issue 2 p. 102-104 Biallelic inactivation of BRCA2 in Fanconi anemia Howlet NG et al. (2002) Science 297: 606–609 First published: 10 March 2003 https://doi.org/10.1034/j.1399-0004.2003.00042_1.xRead the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinked InRedditWechat Volume63, Issue2February 2003Pages 102-104 RelatedInformation

BRCA2 Is Inactivated Late in the Development of Pancreatic Intraepithelial Neoplasia : Evidence and Implications

Patients harboring germline BRCA2 mutations are at an increased risk of developing pancreatic cancer. We investigated the prevalence of biallelic inactivation of BRCA2 in the presumed precursors to invasive pancreatic ductal carcinomas, pancreatic intraepithelial neoplasia (PanIN). Surgical resection specimens from three patients with germline BRCA2 mutations who developed pancreatic ductal adenocarcinoma were studied. Fourteen PanINs were needle-microdissected from paraffin-embedded tissue. DNA was isolated from these microdissected tissues and amplified by primer-mediated pre-amplification. Loss of heterozygosity at the BRCA2 locus was determined by polymerase chain reaction amplification and cycle sequencing. The presence of the wild-type alleles was evaluated at the nucleotide positions of the germline BRCA2 mutations. The K-ras gene was sequenced at codon 12 and 13 to confirm the efficacy of microdissection. By histological evaluation the prevalence of PanINs in these patients was not notably elevated. Loss of the wild-type allele of BRCA2 was present in one high-grade PanIN (PanIN 3), but in none of 13 low-grade PanINs (PanIN 1). In contrast, K-ras mutations were detectable in 7 of the 14 PanINs. These results suggest that biallelic inactivation of the BRCA2 gene is a relatively late event in pancreatic tumorigenesis. In contrast to classical molecular progression models of tumorigenesis, the inactivation of the wild-type allele in a carrier of a recessive tumor susceptibility gene may not always be the first somatic event during the molecular evolution of a cancer. The necessity for earlier genetic alterations before biallelic inactivation of a recessive tumor susceptibility gene such as BRCA2 may explain why affected carriers have normal numbers of neoplastic precursor lesions, a relatively low phenotypic penetrance, and late age of onset of pancreatic and other cancers.