Mutations In DNA Repair Genes Research Articles

Circulating RAS/RAF and DNA-Repair Gene Mutations Associates with High-Risk/Treatment Resistance in Primary Refractory Multiple Myeloma

Background Multiple myeloma (MM) is an incurable plasma cell malignancy with a median overall survival (OS) of 5 years in newly diagnosed (ND) patients. Real-world data reveals that 23% of transplant eligible newly diagnosed MM patients relapse within 12 months of starting first-line bortezomib (1LB) based therapy and of these ~50% will fail secondary therapy and die within 18 months of diagnosis. It is currently impossible to identify these high-risk patients and genomic studies could potentially inform alternative secondary therapeutic options. We propose that circulating tumour DNA (ctDNA) analysis could provide a more holistic approach to gain an insight into the genomics of high-risk patients than bone marrow (BM) tumour DNA analysis in this genetically heterogenous multi-site malignancy. Methods A total of 186 paired peripheral blood plasma and BM samples were obtained at baseline, cycle 3 day 1 (C3D1), end of study (EOS) and/or relapse, whichever appeared earlier, from a Phase II single arm study of carfilzomib-thalidomide-dexamethasone (KTd) in 50 transplant-eligible ND MM patients who were refractory or had a suboptimal response to 1LB (Australasian Leukaemia and Lymphoma Group MM17 trial). Somatic variants were identified with ultra-sensitive targeted amplicon sequencing of BM and plasma for 22-genes known to be mutated in MM. The mutational profiles were combined with the International Staging System (ISS), SKY92 MMProfilerTM risk profile - standard-risk (SR) or high-risk (HR) or EuroFlow minimal residual disease (MRD) status and correlated to progression-free survival (PFS). Longitudinal monitoring of ctDNA variant allele frequency was also plotted to observe alterations in ctDNA kinetics at relapse compared to baseline and C3D1. Results We performed a comparison of the available baseline ctDNA and BM mutational profiles between patients who did relapse (R) (n=18 ctDNA and n=10 BM) or did not relapse (NR) (n=29 ctDNA and n=21 BM). Utilising data derived from all variants identified, there were no significant differences in the relative proportions of specific mutations between R and NR in the BM samples whereas there were significant ctDNA differences between R and NR for both BRAF (p=0.02) and TP53 (p=0.06) mutations (chi-square test). We next performed a comparison of only those ctDNA variants with variant allelic frequencies (VAF) >1%, a threshold known to have a prognostic impact, and identified a statistically significant difference in mutational proportions between R and NR for RAS/RAF (22.2% vs 3.4%, p=0.04) and DNA damage repair genes (DDR) (ATM/ATR/TP53) (55.5% vs 20.6%, p=0.01). Subsequently, we combined ctDNA RAS/RAF and/or DDR mutational detection (>1% VAF, referred to as ctDNA+) with risk status as defined by ISS, SKY92 or MRD. Patients in ISS 2+3/ctDNA+ (compared to ISS 2+3/ctDNA-, ISS 1/ctDNA+, ISS 1/ctDNA-, Figure 1A); SKY92 HR/ctDNA+ (compared to SKY92 HR/ctDNA- and SKY92 SR/ctDNA+ or SKY92 SR/ctDNA-) and MRD+/ctDNA+ (compared to MRD+/ctDNA- and MRD-/ctDNA+ or MRD-/ctDNA-) all had significantly shorter PFS (p<0.01; p<0.01 and p<0.05; respectively, Log-rank tests). Importantly, patients that were ctDNA+ also had a shorter PFS on KTd compared to ctDNA- (p<0.01, 28.4 months for ctDNA+ vs not reached for ctDNA-, Log-rank test, Figure 1B). Conversely, parallel combined analyses with BM mutations revealed no significant prognostic differences. Longitudinal monitoring of ctDNA demonstrated that in 87.5% of patients, 1 or more of the dominant mutations present at the time of relapse were already present at the start of KTd salvage therapy. Conclusions These data demonstrate that combining ctDNA mutational profiling with available platforms for MM risk-stratification significantly enhances the identification of high-risk patients. Moreover, the impact in this context of RAS/RAF and DDR mutations provides a rationale for the design and implementation of novel treatment paradigms utilising RAS/RAF inhibitors or DNA-repair modulators in these high-risk MM patients. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Pathogenic variants in SLF2 and SMC5 cause segmented chromosomes and mosaic variegated hyperploidy

Embryonic development is dictated by tight regulation of DNA replication, cell division and differentiation. Mutations in DNA repair and replication genes disrupt this equilibrium, giving rise to neurodevelopmental disease characterized by microcephaly, short stature and chromosomal breakage. Here, we identify biallelic variants in two components of the RAD18-SLF1/2-SMC5/6 genome stability pathway, SLF2 and SMC5, in 11 patients with microcephaly, short stature, cardiac abnormalities and anemia. Patient-derived cells exhibit a unique chromosomal instability phenotype consisting of segmented and dicentric chromosomes with mosaic variegated hyperploidy. To signify the importance of these segmented chromosomes, we have named this disorder Atelís (meaning - incomplete) Syndrome. Analysis of Atelís Syndrome cells reveals elevated levels of replication stress, partly due to a reduced ability to replicate through G-quadruplex DNA structures, and also loss of sister chromatid cohesion. Together, these data strengthen the functional link between SLF2 and the SMC5/6 complex, highlighting a distinct role for this pathway in maintaining genome stability.

P015 - A dedicated screening for early detection of Prostate cancer (Pca) in men with germline mutations in DNA-Repair Genes (DRG)

P015 - A dedicated screening for early detection of Prostate cancer (Pca) in men with germline mutations in DNA-Repair Genes (DRG)

P008 - Male awareness of prostate cancer risk remains poor in families with germline DNA-repair genes mutations

P008 - Male awareness of prostate cancer risk remains poor in families with germline DNA-repair genes mutations

Deficient mismatch repair is detected in large-to-giant congenital melanocytic naevi: providing new insight into aetiology and diagnosis.

The aetiologies of large-to-giant congenital melanocytic naevi (LGCMN) remain ambiguous. A previous study discovered signatures associated with deficient mismatch repair (dMMR) in patients with LGCMN. However, a screening diagnostic immunohistochemistry (IHC) panel of dMMR in patients with LGCMN has not been performed to date. To identify the MMR status and aetiologies of LGCMN. A total of 110 patients with CMN, including 30 giant CMN, 30 large CMN, 30 medium CMN and 20 small CMN, underwent diagnostic IHC (for MSH6, MSH2, PMS2 and MLH1) screening of dMMR. The control group comprised normal skin samples from 20 healthy people. MMR proteins with little effect (MSH3 and PMS1) on the MMR system were stained in all samples. The surgical procedures conducted on each patient were noted because they might alter the behaviour of CMN and confound the results. Binary logistic regression analyses were performed between the phenotypic data and MMR status to identify associations. Whole-exome sequencing was performed on the main naevi, satellite naevi and normal skin tissues of four patients to detect variants. Mutational signature analyses were conducted to explore the aetiologies of LGCMN. dMMR was detected in 37% (11 of 30) of giant, 23% (7 of 30) of large and 7% (2 of 30) of medium CMNs, but were not identified in small CMNs or normal skin tissues. Moreover, multiple LGCMNs had a much higher dMMR rate than did single LGCMNs. The regression analyses showed that MMR status was significantly associated with CMN size and the presence of satellites, but was not correlated with age, sex, location, satellite diversity or tissue expansion. Notably, the pattern of protein loss in LGCMN mainly consisted of PMS2 loss. Mutational signature analyses detected dMMR-related signatures in patients with LGCMN. Additionally, rare deleterious germline mutations in DNA repair genes were detected in LGCMN, mainly in MSH6, ATM, RAD50, BRCA1 and ERCC8. These germline mutations were single-patient variants with unknown significance. dMMR is one of the aetiologies underlying LGCMN, particularly in patients with giant main lesions and multiple satellite lesions. Further studies are necessary to investigate the role of the DNA repair system, particularly MMR, in LGCMN.

SC142 - A dedicated screening for early detection of prostate cancer in men with germline mutations in DNA-repair genes

SC142 - A dedicated screening for early detection of prostate cancer in men with germline mutations in DNA-repair genes

SC99 - Male awareness of prostate cancer risk remains poor in families with germline mutations in dna-repair genes

SC99 - Male awareness of prostate cancer risk remains poor in families with germline mutations in dna-repair genes

369. GENOMIC ALTERATIONS AND SURVIVAL AFTER TREATMENT OF EAC BY SURGERY WITHOUT CHEMO- OR RADIOTHERAPY

Abstract Prognostic biomarkers for esophageal adenocarcinoma (EAC) remain elusive but may be helpful in treatment planning, as TNM staging often fails to accurately predict survival. Advanced stage patients are treated by peri-operative chemo/radiotherapy; biomarkers associated with survival are thus likely to represent both true prognostic markers as well as markers of response to chemo/radiotherapy. Here we present first-pass genomic findings for a cohort of optimally staged EAC patients treated by surgery alone. DNA was extracted from fresh frozen EAC and matching normal squamous esophageal tissues obtained at esophagectomy from 65 consenting patients who did not receive any neo- or adjuvant chemo- or radiotherapy due to institutional preference at the time of tissue collection. Library preparation and sequencing for a targeted 600 cancer-associated gene panel designed using the Roche/NimbleGen EZ Choice Library NimbleDesign platform were conducted on Illumina-based platforms followed by analysis with an accredited bioinformatics pipeline. The panel design incorporated the entire coding region plus 10 bp of flanking intron of each gene. Mean age 70 yrs; 88% male. All patients underwent an en bloc esophagectomy (mean 35 lymph nodes). TNM (7th ed.) stages were 61% Stage 3, 18% stage 2, 14% stage 1, 6% stage 4. At median 9.5 years follow-up, 20 (31%) patients remained alive. Copy number changes were common, reflecting chromosomal instability. Less than 8% of patients had high tumour mutational burden (&amp;gt;10mut/MB), associated with mutations in DNA repair genes. Commonest somatic mutations included TP53 (HR: 0.43) and LRP1B (HR: 1.7). Pathways implicated included RTK signalling (PIK3CA, EGFR, KRAS), DNA damage (BRCA1, PALB2, MGMT) and histone remodelling (ARID1A, ARID2, KMT2D). Peri-operative treatment means linking genomic changes independent of stage to clinical outcomes is difficult. Neoadjuvant and/or adjuvant treatment is now standard for T2–4 or node positive EAC. This cohort of 65 patients, most of whom had stage 3 disease and all of whom underwent optimal staging with en bloc esophagectomy, represents a unique opportunity to analyze characteristics of EAC without confounding by peri-operative treatment. An EAC-specific DNA sequencing panel approach offers potential for personalized therapy.

Genomic landscape of pleural and peritoneal mesothelioma tumours

BackgroundMalignant pleural and peritoneal mesotheliomas are rare malignancies with unacceptable poor prognoses and limited treatment options. The genomic landscape is mainly characterised by the loss of tumour suppressor genes and mutations in DNA repair genes. Currently, data from next-generation sequencing (NGS) of mesothelioma tumours is restricted to a limited number of cases; moreover, data comparing molecular features of mesothelioma from the pleural and peritoneal origin with NGS are lacking.MethodsWe analysed 1113 pleural mesothelioma and 355 peritoneal mesothelioma samples. All tumours were sequenced with the FoundationOne® or FoundationOne®CDx assay for detection of substitutions, insertion–deletions, copy-number alterations and selected rearrangements in at least 324 cancer genes.ResultsThis analysis revealed alterations in 19 genes with an overall prevalence of at least 2%. Alterations in BAP1, CDKN2A, CDKN2B, NF2, MTAP, TP53 and SETD2 occurred with a prevalence of at least 10%. Peritoneal, compared to pleural mesothelioma, was characterised by a lower prevalence of alterations in CDKN2A, CDKN2B and MTAP. Moreover, we could define four distinct subgroups according to alterations in BAP1 and CDKN2A/B. Alterations in Hedgehog pathway-related genes (PTCH1/2 and SUFU) and Hippo pathway-related gene (NF2) as well as KRAS, EGFR, PDGFRA/B, ERBB2 and FGFR3 were detected in both cohorts.ConclusionHere, we report the molecular aberrations from the largest cohort of patients with mesothelioma. This analysis identified a proportion of patients with targetable alterations and suggests that molecular profiling can identify new treatment options for patients with mesothelioma.

1081P DNA damage response and repair (DDR) gene mutations as an alternative mechanism to generate high TMB in never smoker NSCLC patients

Immune checkpoint inhibitors (IO) single agent or in combination with platinum-based chemotherapy (CT-IO) are standard of care for Stage IV and not oncogene addicted non-small cell lung cancer (aNSCLC) according to PD-L1 expression. The presence of a high tumor mutation burden (H-TMB) is one of the most debated biomarkers for IO response. Smoking-induced harm is a mechanism that generates an H-TMB in aNSCLC smoking patients (S-pts), whereas never-smoking patients (NS-pts) usually have a low TMB and are unresponsive to IO. However, the subgroup of NS-pts with an H-TMB has not yet been well characterized molecularly. We retrospectively collected clinical data from a single-center cohort of 142 aNSCLC pts with PD-L1 ≥ 50% treated with first-line pembrolizumab between January 2017 to March 2021. Next-generation sequencing (NGS) analysis using the FoundationOne®CDx assay (Foundation Medicine, Cambridge, MA, USA) was performed to correlate genetic alterations with clinical characteristics and response outcomes. We classified all detected mutations into eleven main pathways: cell cycle pathway, Hippo pathway, Myc pathway, Notch pathway, Oxidative stress/Nrf2 pathway, PI3K pathway, RTK/RAS/MAP pathway, TGF beta pathway, p53 pathway, beta-catenin/Wnt pathway and DDR pathway. Lastly, we identified the pathways with at least one mutation for each patient and performed enrichment analysis to characterize patients’ subgroups in terms of mutated pathways. With a median follow-up of 22 months (m), mPFS was 9.9 m, and mOS was 10.6 m. There were 111 S-pts and 31 NS-pts. The cohort of S-pts had higher TMB than the NS-pts cohort (TMB average 10.05 vs. 8.86 Mut/Mb). However, a subgroup of 11 NS-pts with high TMB (39-11 Mut/Mb) was identified. This subgroup was particularly enriched in DDR pathway mutations (p-value=0.0016) compared to the rest of the series and the H-TMB/S-pts subgroup. All H-TMB/NS-pts responded to IO treatment with an mPFS of 10.9 m and mOS of 12.7 m. Our data suggest a potential role of DDR signatures as an alternative mechanism to generate H-TMB in NS-pts. This preliminary observation could identify a subgroup of NS-pts responsive to IO and with a better prognosis.

A genome-wide CRISPR-Cas9 knockout screen identifies novel PARP inhibitor resistance genes in prostate cancer.

DNA repair gene mutations are frequent in castration-resistant prostate cancer (CRPC), suggesting eligibility for poly(ADP-ribose) polymerase inhibitor (PARPi) treatment. However, therapy resistance is a major clinical challenge and genes contributing to PARPi resistance are poorly understood. Using a genome-wide CRISPR-Cas9 knockout screen, this study aimed at identifying genes involved in PARPi resistance in CRPC. Based on the screen, we identified PARP1, and six novel candidates associated with olaparib resistance upon knockout. For validation, we generated multiple knockout populations/clones per gene in C4 and/or LNCaP CRPC cells, which confirmed that loss of PARP1, ARH3, YWHAE, or UBR5 caused olaparib resistance. PARP1 or ARH3 knockout caused cross-resistance to other PARPis (veliparib and niraparib). Furthermore, PARP1 or ARH3 knockout led to reduced autophagy, while pharmacological induction of autophagy partially reverted their PARPi resistant phenotype. Tumor RNA sequencing of 126 prostate cancer patients identified low ARH3 expression as an independent predictor of recurrence. Our results advance the understanding of PARPi response by identifying four novel genes that contribute to PARPi sensitivity in CRPC and suggest a new model of PARPi resistance through decreased autophagy.

Selection of Staphylococcus aureus in a murine nasopharyngeal colonization model.

Staphylococcus aureus nasal colonization is a risk factor for infection. A large proportion of the population are identified as potential S. aureus carriers yet we only partially understand the repertoire of genetic factors that promote long-term nasal colonization. Here we present a murine model of nasopharyngeal colonization that requires a low S. aureus inoculum and is amenable to experimental evolution approaches. We used this model to experimentally evolve S. aureus using successive passages in the nasopharynx to identify those genetic loci under selection. After 3 cycles of colonization, mutations were identified in mannitol, sorbitol, arginine, nitrite and lactate metabolism genes promoting key pathways in nasal colonization. Stress responses were identified as being under selective pressure, with mutations in DNA repair genes including dnaJ and recF and key stress response genes clpL, rpoB and ahpF. Peptidoglycan synthesis pathway genes also revealed mutations indicating potential selection for alteration of the cell surface. The murine model used here is versatile to question colonization, persistence and evolution studies.We studied the human pathogen Staphylococcus aureus in our search to determine factors that contribute to its ability to live in the human nose and throat. The anterior nares and nasopharynx are considered primary habitats but we do not understand how the pathogen adapts as it moves from one person to the next. We first determined sustained survival of the pathogen over multiple days in the nasopharynx that might act as a good model for human persistence due to the low numbers of bacteria needed for it to establish. By using successive rounds of colonization of the nasopharynx across different mice we revealed that multiple genetic changes in the S. aureus occurred. These changes were found in genes associated with the cell surface and metabolism and might indicate adaptation to the niche. One gene showed an accumulation of multiple mutations supporting a key contribution in adaptation but the role of the protein it encodes is not yet known. The contribution of these genes and genetic changes are unclear but indicate an area for future research to better understand how this common human pathogen is so successful at human colonization and survival.

A matter of delicate balance: Loss and gain of Cockayne syndrome proteins in premature aging and cancer.

DNA repair genes are critical for preserving genomic stability and it is well established that mutations in DNA repair genes give rise to progeroid diseases due to perturbations in different DNA metabolic activities. Cockayne Syndrome (CS) is an autosomal recessive inheritance caused by inactivating mutations in CSA and CSB genes. This review will primarily focus on the two Cockayne Syndrome proteins, CSA and CSB, primarily known to be involved in Transcription Coupled Repair (TCR). Curiously, dysregulated expression of CS proteins has been shown to exhibit differential health outcomes: lack of CS proteins due to gene mutations invariably leads to complex premature aging phenotypes, while excess of CS proteins is associated with carcinogenesis. Thus it appears that CS genes act as a double-edged sword whose loss or gain of expression leads to premature aging and cancer. Future mechanistic studies on cell and animal models of CS can lead to potential biological targets for interventions in both aging and cancer development processes. Some of these exciting possibilities will be discussed in this review in light of the current literature.

Alterations in DNA damage response and repair genes as potential biomarkers for immune checkpoint blockade in gastrointestinal cancer.

Objective:Immune checkpoint inhibitors (ICIs) have achieved remarkable results in cancer treatments. However, there is no effective predictive biomarker for gastrointestinal (GI) cancer.Methods:We conducted integrative analyses of the genomic and survival data of ICI-treated GI cancer patients from the Memorial Sloan Kettering Cancer Center cohort (MSK-GI, n = 227), the Janjigian cohort (n = 40), and the Peking University Cancer Hospital & Institute cohort (PUCH, n = 80) to determine the possible associations between DNA damage response and repair (DDR) gene mutations and clinical outcomes. Data from The Cancer Genome Atlas database were analyzed to determine the possible correlations between DDR gene mutations and the tumor microenvironment.Results:In the MSK cohort, the presence of ≥ 2 DDR gene mutations was correlated with prolonged overall survival (OS). The Janjigian and PUCH cohorts further confirmed that subgroups with ≥ 2 DDR gene mutations displayed a prolonged OS and a higher durable clinical benefit. Furthermore, the DDR gene mutation load could be considered as an independent prognostic factor, and exhibited a potential predictive value for survival in GI cancer patients treated with ICIs. Mechanistically, we showed that the presence of ≥ 2 DDR gene mutations was correlated with higher levels of tumor mutation burden, neoantigen, and T cell infiltration.Conclusions:The DDR gene mutation status was correlated with favorable clinical outcomes in GI cancer patients receiving ICIs, which could serve as a potential biomarker to guide patient selection for immunotherapy.

Deep Sequencing of Early T Stage Colorectal Cancers Reveals Disruption of Homologous Recombination Repair in Microsatellite Stable Tumours with High Mutational Burdens.

Simple SummaryStage IIIA are rare early T stage colorectal cancers that are not widely reported in genome sequencing studies. We aimed to investigate genomics features in common cancer genes associated with lymph node metastasis from these tumours. We discovered that microsatellite stable tumours with high mutational burdens showed different genomic variant frequencies compared to tumours with low mutation burdens. The high burden microsatellite stable tumours showed co-occurrence of mutations in homologous recombination DNA repair genes that where not observed in the microsatellite stable cancers with low mutational burdens. This finding highlights a potential therapeutic approach for high mutation burden microsatellite stable colorectal cancers given the successful clinical implementation of drugs blocking homologous recombination DNA repair in other cancers.Early T stage colorectal cancers (CRC) that invade lymph nodes (Stage IIIA) are rare and greatly under-represented in large-scale genomic mapping projects. We retrieved 10 Stage IIIA CRC cases, matched these to 16 Stage 1 CRC cases (T1 depth without lymph node metastasis) and carried out deep sequencing of 409 genes using the IonTorrent system. Tumour mutational burdens (TMB) ranged from 2.4 to 77.2/Mb sequenced. No stage-related mutational differences were observed, consistent with reanalysis of The Cancer Genome Atlas (TCGA) Stage I and IIIA datasets. We next examined mutational burdens and observed that the top five cancers were microsatellite stable (MSS) genotypes (mean TMB 49.3/Mb), while the other 16 MSS cancers had a mean TMB of 5.9/Mb. To facilitate comparison with TCGA hypermutator CRC, we included four microsatellite instability-high (MSI-H) samples with the high mutation burden MSS cases to form a TMB-High group. Comparison of TMB-High with TMB-Low groups revealed differences in mutational frequency of ATM, ALK, NSD1, UBR5, BCL9, CARD11, KDM5C, MN1, PTPRT and PIK3CA, with ATM and UBR5 validated in reanalysis of TCGA hypermutator Stages I and IIIA samples. Variants in ATM were restricted to the TMB-High group, and in four of five MSS specimens, we observed the co-occurrence of mutations in homologous recombination repair (HRR) genes in either two of ATM, CDK12, PTEN or ATR, with at least one of these being a likely pathogenic truncating mutation. No MSI-H specimens carried nonsense mutations in HRR genes. These findings add to our knowledge of early T stage CRC and highlight a potential therapeutic vulnerability in the HRR pathway of TMB-H MSS CRC.

Germline Mutations in Patients With Early-Onset Prostate Cancer.

ObjectiveTo investigate the inherited mutations and their association with clinical features and treatment response in young-onset prostate cancer patients.MethodTargeted gene sequencing on 139 tumor susceptibility genes was conducted with a total of 24 patients diagnosed with PCa under the age of 63 years old. Meanwhile, the related clinical information of those patients is collected and analyzed.ResultsSixty-two germline mutations in 45 genes were verified in 22 patients. BRCA2 (20.8%) and GJB2 (20.8%) were found to be the most frequently mutated, followed by CHEK2, BRCA1, PALB2, CDKN2A, HOXB13, PPM1D, and RECQL (8.3% of each, 2/24). Of note, 58.3% (14/24) patients carry germline mutations in DNA repair genes (DRGs). Four families with HRR (homologous recombination repair)-related gene mutations were described and analyzed in detail. Two patients with BRCA2 mutation responded well to the combined treatment of androgen deprivation therapy (ADT) and radiotherapy/chemotherapy.ConclusionMutations in DRGs are more prevalent in early-onset PCa with advanced clinical stages, and these patients had shorter progression-free survival. ADT Combined with either radiotherapy or chemotherapy may be effective in treating PCa caused by HRR-related gene mutations.

Germline genetics of prostate cancer.

An important fraction (>/~10%) of men with high-risk, localized prostate cancer and metastatic prostate cancer carry germline (heritable) pathogenic and likely pathogenic variants (also known as mutations) in DNA repair genes. These can represent known or suspected autosomal dominant cancer predisposition syndromes. Growing evidence suggests that pathogenic variants in key genes involved in homologous recombination and mismatch DNA repair are important in prostate cancer initiation and/or the development of metastases. Here we provide a comprehensive review regarding individual genes and available literature regarding risks for developing prostate cancer, and discuss current national guidelines for germline genetic testing in the prostate cancer population and treatment implications. The association with prostate cancer risk and treatment implications is best understood for those with germline mutations of BRCA2, with emerging data supporting associations with ATM, CHEK2, BRCA1, HOXB13, MSH2, MSH6, PALB2, TP53 and NBN. Treatment implications in the metastatic castration resistant prostate cancer setting include rucaparib and olaparib, and pembrolizumab with potential clinical trial opportunities in earlier disease settings. The data summarized in this review has led to the expansion of national guidelines for germline genetic testing in prostate cancer. We review these guidelines, and discuss the importance of cascade genetic testing of relatives, diverse populations with attention to inclusion, as well as prostate cancer screening updates and clinical trial opportunities for men who carry genetic risk factors for prostate cancer.

MODL-04. Drug screening in Disorders with Abnormal DNA Damage Response/Repair (DADDR) andin vivo validation

INTRODUCTION: Disorders with Abnormal DNA Damage Response/Repair (DADDRs) are inherited conditions caused by constitutional mutations of DNA damage response and repair genes and are characterized by an increased cancer risk. Furthermore, affected individuals also show an elevated risk of secondary neoplasms as well as excessive toxicity, poor therapy response and increased mortality when treated with standard radiation and chemotherapy regimens. The main aim of this project is to screen for potential novel chemotherapeutic approaches for these cancer entities, and to employ faithful PDX models for in vivo validation. METHODS: In vitro drug screening was performed using a custom library composed of 345 compounds targeting 61 different proteins. For two specific DADDRs, Li-Fraumeni syndrome (LFS) and Constitutional Mismatch Repair Deficiency (CMMRD), two cancerous (glioblastoma and medulloblastoma) and one non-cancerous cell lines were selected to model each of these conditions. Performance of each drug was assessed based on its efficacy (sensitivity score) and genotoxicity (micronucleus assay). For DADDR PDX model establishment tumor material from DADDR patients is currently being injected orthotopically (brain tumors) or subcutaneously (non-brain tumors) into NSG mice. Following engraftment and expansion, the PDX models will be characterized molecularly and compared with original patient material. RESULTS AND OUTLOOK: In vitro screening revealed n=26 drugs that fulfilled the following criteria: a) favorable toxicity in cancerous cell lines compared to non-cancerous cell lines, b) little to no genotoxic effect in non-cancerous cell lines. These characteristics qualify them as potentially suitable candidates for novel therapeutic approaches specifically for DADDR patients. The hits included inhibitors of ATM/ATR, CHK1/CHK2, DHFR, mTOR and PI3K, as well as microtubule-associated compounds. Combination testing and further validation of these hits using disease-specific in vitro and in vivo PDX models is ongoing.

Mutation spectrum and rates of variants of uncertain significance among African American males undergoing prostate cancer germline testing: Need for equity in genetic testing.

10502 Background: Germline testing (GT) for prostate cancer (PCA) is central to metastatic disease management, PCA screening strategies, and hereditary cancer assessment. African American (AA) males have a higher burden of PCA, yet have lower engagement in germline testing which limits understanding of genetic contribution to PCA. Here we evaluated the germline spectrum of AA and White males with PCA undergoing clinical multigene panel testing (MGPT) to inform germline testing strategies with attention to equity. Methods: Study participants included AA men and White men with PCA who underwent a 14-gene MGPT between April 2012 - December 2020 at a clinical diagnostic laboratory (Ambry Genetics). Exclusions were men with known pathogenic variants reported in their families or who had prior genetic testing. MGPT included: ATM, BRCA1, BRCA2, CHEK2, EPCAM, HOXB13, MLH1, MSH2, MSH6, NBN, PALB2, PMS2, RAD51D, TP53. Sanger or next generation sequencing analysis was performed per standard clinical testing protocol. Variant classification was per ACMG 5-tier system. Descriptive statistics summarized results with counts and percentages for categorical variables and mean and standard deviation for continuous variables. Data were compared with Fisher’s exact, Chi-squared, two proportion z-test, or two sample t-test, as appropriate. Significance level was set a priori at 0.05. Results: The dataset included genetic and clinical data from 427 males who had undergone MGPT: White males (n = 190; 45.5%) and AA males (n = 237; 55.5%). Mean age at diagnosis was 59 + 9.3 years. Among men whose Gleason score was indicated (72%), 47% had Gleason &gt; = 8. Majority of men indicated having a 1st/2nd degree relative with PCA (68.97%) or 1st/2nd degree relative with any cancer (99.2%). In the entire cohort, 8.2% tested positive for a pathogenic/likely pathogenic variant; AA males (n = 14, 5.91%) and White males (n = 21, 11.05%). VUS only was reported in 21.31% of the overall cohort with a significant difference noted between AA and White males (25.32% vs. 16.32%, respectively; p = 0.0238). Mutation spectrum in AA males included: BRCA2 (n = 7), PALB2 (n = 3), ATM (n = 3), and BRCA1 (n = 1). Among White males, a wider spectrum of mutations was observed: BRCA2 (n = 6), ATM (n = 5), HOXB13 (n = 5), CHEK2 (n = 2), TP53 (n = 1), and NBN (n = 2). The proportion of AA males with multiple VUS was significantly higher than for Caucasian males (5.1% vs. 0.53%, p = 0.003). Conclusions: Clinical germline testing among AA males reveals a narrow spectrum of mutations in key DNA repair genes, with important implications for precision therapy and hereditary cancer assessment. Furthermore, AA males had significantly higher rates of multiple VUS, indicating critical need for greater inclusion of diverse populations in genetic studies to discern the pathogenic spectrum contributing to PCA aggressiveness and risk.

Comprehensive genomic analysis of early and late-onset hepatocellular carcinoma.

e16186 Background: Hepatocellular carcinoma (HCC) accounts for 90% of primary liver cancer and is a leading cause of cancer-related death worldwide. HCC is highly therapy-resistant, and biomarker-driven therapies are emerging as important treatment options. Risk factors have been implied to distinguish early and late-onset patients. A high prevalence of non-cirrhotic HCC attributed to hepatitis B virus infection was found in young Asian patients. In late-onset patients, genetic aberrations accumulated with age in liver cirrhosis and other chronic liver diseases could provide the basis of tumorigenesis. Thus, diverse genomic alteration modes may underlie HCC of different onset ages, but the analysis is lacking. This study aims to explore genomic distinctions underlying early and late-onset HCC, thus facilitating personalized biomarker-driven treatments. Methods: The plasma and tumor samples from 222 Chinese HCCs underwent genomic profiling with hybridization capture-based targeted next-generation sequencing. The patients were categorized into early (male &lt; 40 years or female &lt; 50 years) or late (male ≥ 40 years or female ≥ 50 years) onset in accordance with the American Association for the Study of Liver Diseases guideline. We compared the clinical and molecular characteristics and explored differences between the early and late-onset cohorts. Results: The late-onset cohort accounts for 83.3% (185/222) of all HCC cases, and its male incidence rate is significantly higher than that of early-onset (88.6% vs 56.8%, p&lt; 0.0001). More younger cases have a family history of HCC (21.6% vs 14.6%). The mean somatic alteration numbers per patient are comparable between early and late-onset (8.30 vs 9.92). While TP53, TERT, and MCL1 are the most frequently mutated genes in both cohorts, we identified eight genes with significantly higher mutation frequencies in early-onset. OncoKB Levels 1 to 4 actionable alterations are present in 48.7% and 44.3% of younger and older patients, respectively, whereas the early-onset cohort has a significant enrichment of actionable MDM2 alterations (10.8% vs 1.1%, p= 0.0078). The prevalence of DNA Damage Response and Repair (DDR) gene mutations (35.1% vs 48.6%) and tumor mutation burden (TMB, mean: 4.17 muts/Mb vs 8.11 muts/Mb) are elevated in older patients. Notably, individuals harboring DDR mutations are associated with higher TMB in late-onset (mean TMB in DDR-mutated: 10.44 vs DDR- wildtype: 5.90, p= 0.0016) but not early-onset (mean TMB in DDR-mutated: 3.47 vs DDR- wildtype: 4.54, p= 0.280). Conclusions: Tumors from early and late-onset HCC demonstrated differences in genes and other biomarkers relevant to cancer biology and response to therapy. Specifically, DDR-mutated patients in the late-onset cohort are associated with higher TMB and may benefit from combining targeted and immunotherapy. Future studies are warranted to examine the response to biomarker-driven treatment strategies.