CAD is Associated with Cancer Prognosis and Promotes Enzalutamide Resistance in Prostate Cancer.

e15032 Background: Homologous recombination deficiency (HRD) is an event triggered by impairment of the homologous recombination repair (HRR) pathway which acts on DNA double-strand breaks and interstrand cross-links (ICL). Although HRD has been shown to elevate the overall genomic instability in tumors inducing favorable responses to immune checkpoint inhibitors (ICI), its clinical utility is observed in specific cancer types like breast, ovarian, low-grade glioma, testicular germ cell tumors and kidney cancers. On the contrary, in many other cancer types, HRD is conducive to the development of immune-cold tumor microenvironment leading to unfavorable treatment responses to ICI. We present, HRD predictive scores with the corresponding IO biomarkers viz. microsatellite instability (MSI) and tumor mutation burden (TMB) pan-cancers. Methods: Retrospectively, we investigated the biomarker profile (HRD, MSI, TMB) and genomic (HRR pathway genes) profiles of 642 pan-cancer patients using a comprehensive genomic assay using OncoIndx. Results: Of the cohort of 642 pan-cancer patients, a total of 12.3% (n = 79/642) of patients were detected with high HRD scores, another 16.0% (n = 103/642) were detected with intermediate HRD scores and while 71.7% (n = 460/642) of patients showed low HRD scores. Among the cohorts of high, intermediate and low HRD scores, BRCA1/2 mutation-positive patients were 6.3% (n = 5/79), 5.8% (n = 6/103), and 5.2 (n = 24/460) respectively and HRR gene mutation-positive patients were 17.7% (n = 14/79), 25.2% (n = 26/103), 17.17% (n = 79/460) respectively. Most importantly, the immune-oncology biomarkers MSI and TMB scores were high only in 1.3% (n = 1/79) and 8.9% (n = 7/79) in HRD-high patients which were not significant compared to 1.7% (n = 8/460) and 10.4% (n = 48/460) observed in HRD-low patient cohort. Even in the cohort of patients with intermediate HRD scores, MSI and TMB did not vary significantly. Overall, no significant correlation was observed between high HRD scores vs BRCA1/2 mutations, HRR pathway gene mutations, MSI and TMB statuses. Thus, HRD scores could be predicted high, irrespective of all the associated biomarkers and pathway mutations. This indicates the utility of additional treatment options in BRCA1/2 wild-type or HRR pathway gene wild-type patients. Conclusions: Although HRD-high patients could be predictive of favorable PARPi and platinum-based therapies, their role in immune activation and ICI therapy response should be carefully considered. Even at a high score, HRD seems to be inducing non-inflammatory tumor microenvironment as opposed to triggering novel cell surface antigens and high TMB aiding in immunotherapy response. However, HRD as an individual biomarker alone adds immense therapeutic benefits even among BRCA-negative patients who could be potential for PARPi/platinum-based therapy.

Background: Recent studies suggest that glucocorticoid receptor (GR) activation can cause enzalutamide resistance in advanced prostate cancer (PCa) via functional bypass of androgen receptor (AR) signaling. However, the specific molecular mechanism(s) driving this process remain unknown. In an effort to identify drivers of prostate cancer progression, in a previous study, we determined that TBX2, a developmental T-box transcription factor (TF) master regulator, is over-expressed in CRPC and drives bone metastatic progression. A recent report confirmed that TBX2 and GR are two of the four TFs that drive enzalutamide resistance in advanced PCa. Our current study demonstrates that TBX2 with known repressor and activator functions, is the molecular switch that represses AR levels while activating GR expression thereby resulting in the replacement of AR signaling to control tumor growth. Methods: We genetically modulated TBX2 using multiple approaches: a) dominant negative, DN, to block TBX2 (TBX2DN), and b) overexpression, OE, to increase TBX2 expression (TBX2OE), c) shRNA mediated knockdown (shTBX2). RNA-seq was performed, and qRT-PCR, Western blot and immunohistochemical (IHC) analyses were used for validation. Further, we used chromatin immunoprecipitation (ChIP) and site directed mutagenesis (SDM) to confirm TBX2 binding on the AR promoter. We also used co-immunoprecipitation (Co-IP) to determine protein partners of TBX2. Results: Mechanistically, our studies revealed that TBX2 bound to the promoters of both AR and GATA2, an AR coregulator, thereby resulting in a bimodal repression of AR expression. Conversely, TBX2 upregulated GR via direct GR promoter binding and TBX2-GR protein-protein interaction. Together, concurrent repression of the AR and activation of GR resulted in enzalutamide resistance. Importantly, we found that SP2509, an allosteric inhibitor of the demethylase-independent function of LSD1, a TBX2-interacting protein in the COREST complex, can disrupt both TBX2-LSD1 and TBX2-GR protein-protein interactions thereby uncovering a unique mode of SP2509 action in CRPC. Together, our study supports a molecular model of CRPC wherein: 1) TBX2, LSD1 and GR proteins interface with each other, and 2) pharmacological inhibition of LSD1 blocks the TBX2-driven AR-to-GR switch through disruption of TBX2-GR interaction. Conclusions: In summary, our study identifies TBX2 as the molecular switch that drives the AR to GR signaling bypass thereby conferring enzalutamide resistance. Further, our study provides key insights into a potential therapeutic modality for targeting the AR to GR signaling switch via disruption of the TBX2-LSD1 and TBX2-GR protein-protein interactions Citation Format: Sayanika Dutta, Girijesh Kumar Patel, Hamed Khedmatgozar, Daniel Latour, Jonathan Welsh, Manisha Tripathi, Srinivas Nandana. A TBX2-driven signaling switch from androgen receptor to glucocorticoid receptor confers enzalutamide resistance in prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6603.

e17569 Background: Molecular classification of endometrial cancer has been applied in patient stratification and treatment strategy. Although the Cancer Genome Atlas project and other genomic studies have established comprehensive molecular classification, its genomic characteristics in Chinese endometrial cancer remain unclear. Methods: Tumor tissue and matched white blood cells from 316 patients with endometrial cancer underwent next-generation sequencing (NGS), which targeted the whole coding region of 733 or 381 genes. Endometrial cancer was classified into four subtypes according to genomic characteristics: polymerase (POLE) ultramutated, microsatellite instability (MSI), TP53 wild type (TP53wt), and TP53 mutant (TP53mut). Tumor mutation burden (TMB) was calculated based on the number of somatic single nucleotide variants and indels in examined coding regions. Deleterious or suspected deleterious genes were included for analysis. Genomic instability was also evaluated with Homologous Recombination Deficiency (HRD) score by over 10, 000 single-nucleotide polymorphisms distributed across human genome. HRD algorithm combined loss of heterozygosity score (LOH), telomeric allelic imbalance score (TAI) and large-scale state transition score (LST). Results: The 316 endometrial cancer patients were divided into four subtypes: POLE ultramutated (16, 5.06%), MSI tumors (70, 22.2%), TP53wt (131, 41.5%), and TP53mut (99, 31.3%). Median TMB was 26.5 mut/Mb in overall cohort and POLE ultramutated subtype possessed the highest TMB (181 mut/Mb), followed by MSI (54.1 mut/Mb), TP53mut (7.11 mut/Mb) and TP53wt (6.61 mut/Mb) subtypes. POLE, PTEN, LRP1B, BRCA2 and ATRX were the top frequently mutated genes in POLE ultramutated subtype, which mutation rate are more that 80%. The most frequent mutations were detected in ARID1A, PTEN, PIK3CA in MSI subtype, TP53, PIK3CA, PTEN in TP53mut subtype, and PTEN, PIK3CA, ARID1A in TP53wt subtype. HRD score was significantly higher in TP53mut subtype, followed by TP53wt, MSI and POLE ultramutated subtype (median HRD score, 21.7, 6.15, 3.65 and 0; P < 0.001). Conclusions: Our study revealed the heterogeneous genomic characteristics of four molecular subtypes in Chinese endometrial cancer. POLE ultramutated and MSI subtypes display higher TMB. TP53mut subtype showed genome features of HRD and would likely benefit from HRD-targeted therapy.

When should we order a next generation sequencing test in a patient with cancer?

Homologous recombination deficiency (HRD) leads to DNA double‐strand breaks and can be exploited by the use of poly (ADP‐ribose) polymerase (PARP) inhibitors to induce synthetic lethality. Extending the original therapeutic concept, the role of HRD is currently being investigated in clinical trials testing immune checkpoint blockers alone or in combination with PARP inhibitors, but the relationship between HRD and immune cell context in cancer is incompletely understood. We analyzed the association between immune cell composition, gene expression, and HRD in 9,041 tumors of 32 solid cancer types from The Cancer Genome Atlas (TCGA). The numbers of genomic scars were quantified by the HRD sum score (HRDsum) including loss of heterozygosity, large‐scale state transitions, and telomeric allelic imbalance. The T‐cell inflamed gene expression profile correlated weakly, but significantly positively, with HRDsum across cancer types (ρ = 0.17). Within individual cancer types, a significantly positive correlation was observed only in breast cancer, ovarian cancer, and four other cancer types, but not in the remaining 26 cancer types. HRDsum and tumor mutational burden (TMB) correlated significantly positively across cancer types (ρ = 0.42) and within 18 cancer types. HRDsum and a proliferation metagene correlated significantly positively across cancer types (ρ = 0.52) and within 20 cancer types. Mismatch repair deficiency and HRD as well as proofreading deficiency showed a high level of exclusivity. High HRD scores were associated with an immunologically activated tumor microenvironment only in a minority of cancer types. Our data favor the combination of genetic markers, complex genomic markers (including HRDsum and TMB), and other molecular markers (including proliferation scores) for a precise and comprehensive read‐out of the tumor biology and an individually tailored treatment.

e14585 Background: Genome-wide homologous recombination deficiency (HRD) score is an important parameter to select patients for HRR pathway inhibitors. HRD scores are independent therapeutic predictors unlike tumor mutation burden (TMB), and microsatellite instability (MSI) values to stratify tumors for predicting immunogenicity. Since solid tumors often choose the hallmark of immune evasion to disseminate to distant tissues, their identification and treatment through genomic signatures for immunotherapy is essential. Low TMB and MSI values are often associated with immune evasion and immune cold tumors. For such patients HRD scores can be important determinants to inform on the therapeutic potential of HRR pathway inhibitors and immune checkpoint inhibitors (ICI). In this study, we retrospectively investigated solid tumors with metastatic phenotypes exhibiting microsatellite stable (MSS), MSI-Low and TMB low phenotypes. The presence of HRR pathway deficiency in these patients may lead to chromosomal instabilities and cell surface neo-antigens thereby offering potential therapeutic benefit to PARP inhibitors and ICI. Methods: 53 metastatic cancer patients were retrospectively analysed for genome-wide HRD, TMB and MSI scores based on OncoIndx comprehensive gene panel (CGP). OncoIndx CGP targets 1080 cancer related genes along with 47 HRR genes and 1600 MSI signature sites. HRD, TMB and MSI scores were determined by sequencing the individual sample libraries in pair end mode on Illumina Nextseq platform (depth 5500X). Cutoff scores HRD high (≥50), TMB high (≥10 Mutations/MB), MSI high (≥20). Results: A cohort of 53 solid tumor patients were evaluated retrospectively of which 71.6% (n=38) patients showed metastasis (brain, Popliteal fossa, skeletal, and nodal metastasis). Of these, 9.4% (n=5) patients were detected with MSI-high, 56.6% (n=30) were MSI-Low and 1.8% (n=1) were MSS. 13.2% (n=7) patients were TMB-High, 3.7% (n=2) were TMB intermediate and 41.0% (n=22) were TMB-Low. Most importantly, 41.0% (n=22) patients were both MSI and TMB low thus transforming the tumor suggestively immune-cold. Only 22.7% (n=5) patients showed PD-L1 expression on IHC with scores ranging from TPS: 2% to 20%. In this dominantly immune-cold patient cohort, 40.9% (n=9) patients showed high/intermediate HRD (22.7% high (n=5); 18.18% Intermediate (n=4)). Conclusions: The presence of HRD in 40.9% patients in the dominant immune-cold patients was observed with increased chromosomal instability and cell surface neo-antigens. Thus, HRD could potentially transform tumors to become immune-hot to benefit from PARP inhibitors and ICI.

Background: Enzalutamide, an FDA-approved androgen receptor blocker, is commonly prescribed for advanced prostate cancer which slows down prostate tumor growth. However, therapeutic benefit of enzalutamide is temporary because enzalutamide-resistant prostate cancer (ERPC) invariably develops which is incurable, primarily because currently available therapies cannot effectively kill ERPC cells. Molecular basis behind enzalutamide-resistance is not clearly understood, which is delaying progress towards development of new therapies. Thus, proper molecular characterization of ERPC cells is an urgent and unmet medical need to find appropriate targets to improve the current state of ERPC therapy. Methods: We developed an ERPC model by chronically treating prostate cancer cells to mimic the clinical conditions of Enzalutamide resistance. These ERPC cells were used for comprehensive gene expression analysis by Illumina Hi-Seq whole genome gene-expression array. Hits were confirmed by RT-PCR and Western blot. Regulation of expression and pro-cancer effects of new hits were determined by overexpression and/or treating cells with shRNA and analyzing cell viability, soft-agar colony formation, apoptosis, and effects on downstream targets. Results: Transcriptional profiling revealed that Tribbles 2 (Trib2), a pseudokinase, is overexpressed in ERPC cells. Elevated level of Trib2 was also observed in enzalutamide treated PDX tumors in mice, and in prostate tumors from patients who were treated with enzalutamide. Inhibition of Trib2 by shRNA effectively kills ERPC cells, suggesting that Trib2 plays an important role in ERPC. We found that the Trib2 protein level is especially higher in prostate cancer cells where the AR activity is either low, or absent due to genetic changes. Moreover, transfection and re-expression of the AR gene in AR-negative cells decreases Trib2 protein level, indicating that the expression of Trib2 is negatively regulated by androgenic signaling. Interestingly, forced overexpression of Trib2 results in faster prostate cancer cell growth and makes the cells completely resistant to enzalutamide, and inhibition of Trib2 by shRNA or chemical inhibitor decreases viability and re-sensitizes these cells to enzalutamide. Conclusion: Collectively, our findings reveal that Trib2 is overexpressed in ERPC cells and tumors, and suggest that Trib2 may turn out to be a novel, promising molecular target for therapy of enzalutamide-resistant, lethal prostate cancer. Citation Format: Jitender Monga, Parshva Sanghvi, Jagadananda Ghosh. Overexpression of Tribbles 2 enhances prostate cancer cell growth and contributes to enzalutamide resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1325.

Association of BRCA1/2, homologous recombination deficiency, and PD-L1 with clinical outcomes in patients receiving atezolizumab versus placebo combined with carboplatin, paclitaxel, and bevacizumab for newly diagnosed ovarian cancer: exploratory analyses of IMagyn050/GOG3015/ENGOT-ov39

IntroductionTo investigate the molecular mechanisms underlying enzalutamide resistance in castration-resistant prostate cancer (CRPC) and explore potential therapeutic strategies to overcome resistance.MethodsWe conducted comprehensive bioinformatic analysis using LNCaP/enzalutamide-resistant cells to identify key pathways associated with resistance. Functional validation was performed through targeted inhibition of the elongation of very-long chain fatty acid protein 2 (ELOVL2), followed by assays to assess cancer cell proliferation and enzalutamide sensitivity. Mechanistic studies were conducted to evaluate the impact of ELOVL2 on the ubiquitin-proteasome system and AR signaling pathways.ResultsBioinformatic analysis revealed that activation of fatty acid metabolism, particularly through upregulation of ELOVL2, plays a critical role in driving enzalutamide resistance in PCa. Functional studies demonstrated that targeted inhibition of ELOVL2 significantly suppressed cancer cell proliferation and restored enzalutamide sensitivity in resistant cells. Mechanistically, ELOVL2 facilitates enzalutamide resistance by impairing the ubiquitin-proteasome system, leading to the subsequent activation of AR signaling pathways.DiscussionOur findings demonstrate that ELOVL2 drives enzalutamide resistance in CRPC by stabilizing AR through inhibition of ubiquitin-proteasome-mediated degradation. Targeting ELOVL2 represents a promising therapeutic strategy to overcome resistance in CRPC, with potential to improve clinical outcomes for patients.

Because only a subset of cancer patients can benefit from immunotherapy, identifying predictive biomarkers of ICI therapy response is of utmost importance. We analyzed the association between hemoglobin (HGB) levels and clinical outcomes in 1,479 ICIs-treated patients across 16 cancer types. We explored the dose-dependent associations between HGB levels and survival and immunotherapy response using the spline-based cox regression analysis. Furthermore, we investigated the associations across subgroups of patients with different clinicopathological characteristics, treatment programs and cancer types using the bootstrap resampling method. HGB levels correlated positively with clinical outcomes in cancer patients receiving immunotherapy but not in those without immunotherapy. Moreover, this association was independent of other clinicopathological characteristics (such as sex, age, tumor stage and tumor mutation burden (TMB)), treatment program and cancer type. Also, this association was independent of the established biomarkers of immunotherapy response, including TMB, PD-L1 expression and microsatellite instability. The combination of TMB and HGB level are more powerful in predicting immunotherapy response than TMB alone. Multi-omics analysis showed that HGB levels correlated positively with antitumor immune signatures and negatively with tumor properties directing antitumor immunosuppression, such as homologous recombination defect, stemness and intratumor heterogeneity. The HGB measure has the potential clinical value as a novel biomarker of immunotherapy response that is easily accessible from clinically routine examination. The combination of TMB and HGB measures have better predictive performance for immunotherapy response than TMB.

While androgen deprivation therapy (ADT) continues to be a fundamental aspect of prostate cancer treatment, the development of castration-resistant prostate cancer (CRPC) emphasizes the necessity for a more profound understanding of the tumor microenvironment (TME). Normal fibroblasts (NFs) and cancer-associated fibroblasts (CAFs) were isolated and characterized from normal control and prostate cancer specimens, respectively. PC3 and DU145 cells, and the corresponding enzalutamide resistant counterparts, PC3-EnzR and DU145-EnzR, were co-cultured with NFs or CAFs to evaluate the effects of TME in driving enzalutamide resistance. Cell viability of prostate cancer cells was examined by MTT assay. The study also utilized recombinant human neuregulin-1 (NRG1) protein and siRNA to modulate NRG1 expression in CAFs. RT-qPCR, Western blot, and ELISA were employed to assess gene and protein expressions related to the NRG1-HER3 signaling pathway and its association with enzalutamide resistance. CAFs significantly promoted cell growth and enzalutamide resistance of PC3-EnzR and DU145-EnzR cells through substantial increased secretion of NRG1 by CAFs. Co-culturing enzalutamide-resistant prostate cancer cells (PC3-EnzR and DU145-EnzR) with CAFs further enhanced enzalutamide resistance, as evidenced by elevated IC50 values. Inhibition of NRG1 in CAFs attenuated their impact on enzalutamide resistance, providing insight into the role of NRG1 in mediating the crosstalk between CAFs and prostate cancer in the context of enzalutamide resistance. This study elucidates the pivotal role of CAF-secreted NRG1 in promoting enzalutamide resistance in prostate cancer, providing valuable insights for developing targeted therapeutic strategies to overcome resistance in advanced prostate cancer.

e23520 Background: Assessing molecular alterations in solid tumors is essential for providing the best care in precision oncology. CGP tests utilize next-generation sequencing (NGS) to detect clinically relevant alterations and molecular signatures that are increasingly utilized in cancer careand can be performed in-house, which decreases test turnaround time (TAT) and costs. A paucity of studies have documented the experience of in-house testing at academic centers in Brazil. Methods: The TruSight Oncology (TSO) 500 assay/TSO 500 HRD are research use only (RUO) CGP assays that were validated for the detection of small variants (SVs), copy number variants (CNVs), microsatellite instability (MSI), tumor mutation burden (TMB) and genomic instability score (GIS) in DNA and gene fusions/splice variants in RNA in the NextSeq 500 system. Secondary analysis was performed with Illumina Connected Analytics. Tertiary analysis was performed with Illumina Connected Insights (ICI) and Sophia DDM. TMB ≥ 10mut/Mb was defined as TMB-High and GIS ≥ 42 was homologous recombination deficient (HRD). Results: We performed CGP on 40 FFPE samples (16 with HRD) with variable quality and block age most of which had known alterations detected by other genomics/molecular tests: 17 TNBC (16 paired DNA and RNA, 1 DNA only), 18 lung cancer (13 paired DNA and RNA, 5 DNA only), 1 endometrium cancer (DNA only, POLE mutated, 4 replicates), 1 colorectal cancer (DNA only, MSI unstable) and 11 sarcomas (RNA only). 84%, 84%, 90% and 89% of samples with DNA integrity number (DIN) > 2.5 were qualified for analysis of SVs/TMB, MSI, CNVs, and GIS, respectively, while for samples with DIN < 2.5 these values felt to 47%, 74%, 68% and 43%, respectively. RNA isolated from blocks dated up to 5 y.o. were qualified in 90% of cases while from older blocks only 6%. The 4 replicate (single sample) analysis showed 82% and 83% overall variant concordance in the ICI and Sophia DDM software, respectively. All previously known oncogenic alterations (SVs ≥5% VAF, fusions/splice, MSI, TMB) were detected (qualified samples) and with similar performance in ICI and Sophia, respectively: concordance 0.91/p < 0.0001 vs 0.94/p < 0.0001; sensitivity 100% vs 100%; specificity 98% vs 100%. TMB had 100% concordance with previous TMB results. Of note, 73% (8/11) TNBC samples analyzed for GIS were HRD and 75% (6/8) explained by BRCA1 germline mutation (25%) and BRCA1or RAD51C somatic promoter methylation (75%). Conclusions: This study demonstrates the utility of CGP and HRD testing in identifying multiple molecular alterations in FFPE tissue samples with high sensitivity and specificity. Pre-analytical variables directly impact data generation. BRCA1/RAD51C promoter methylation showed to be a potential biomarker for selecting metastatic TNBC patients for PARP inhibitor therapies. Offering CGP can potentially bring precision oncology to more patients with cancer in Brazil.

<div>AbstractPurpose:<p>To explore whether patients with <i>BRCA1/2</i>-mutated or homologous recombination deficient (HRD) ovarian cancers benefitted from atezolizumab in the phase III IMagyn050 (NCT03038100) trial.</p>Patients and Methods:<p>Patients with newly diagnosed ovarian cancer were randomized to either atezolizumab or placebo with standard chemotherapy and bevacizumab. Programmed death-ligand 1 (PD-L1) status of tumor-infiltrating immune cells (IC) was determined centrally (VENTANA SP142 assay). Genomic alterations, including deleterious <i>BRCA1/2</i> alterations, genomic loss of heterozygosity (gLOH), tumor mutation burden (TMB), and microsatellite instability (MSI), were evaluated using the FoundationOne assay. HRD was defined as gLOH ≥ 16%, regardless of <i>BRCA1/2</i> mutation status. Potential associations between progression-free survival (PFS) and genomic biomarkers were evaluated using standard correlation analyses and log-rank of Kaplan–Meier estimates.</p>Results:<p>Among biomarker-evaluable samples, 22% (234/1,050) harbored <i>BRCA1/2</i> mutations and 46% (446/980) were HRD. Median TMB was low irrespective of <i>BRCA1/2</i> or HRD. Only 3% (29/1,024) had TMB ≥10 mut/Mb, and 0.3% (3/1,022) were MSI-high. PFS was better in <i>BRCA2</i>-mutated versus <i>BRCA2</i>–non-mutated tumors and in HRD versus proficient tumors. PD-L1 positivity (≥1% expression on ICs) was associated with HRD but not <i>BRCA1/2</i> mutations. PFS was not improved by adding atezolizumab in <i>BRCA2-</i>mutated or HRD tumors; there was a trend toward enhanced PFS with atezolizumab in <i>BRCA1</i>-mutated tumors.</p>Conclusions:<p>Most ovarian tumors have low TMB despite <i>BRCA1/2</i> mutations or HRD. Neither <i>BRCA1/2</i> mutation nor HRD predicted enhanced benefit from atezolizumab. This is the first randomized double-blind trial in ovarian cancer demonstrating that genomic instability triggered by <i>BRCA1/2</i> mutation or HRD is not associated with improved sensitivity to immune checkpoint inhibitors.</p></div>

<div>AbstractPurpose:<p>To explore whether patients with <i>BRCA1/2</i>-mutated or homologous recombination deficient (HRD) ovarian cancers benefitted from atezolizumab in the phase III IMagyn050 (NCT03038100) trial.</p>Patients and Methods:<p>Patients with newly diagnosed ovarian cancer were randomized to either atezolizumab or placebo with standard chemotherapy and bevacizumab. Programmed death-ligand 1 (PD-L1) status of tumor-infiltrating immune cells (IC) was determined centrally (VENTANA SP142 assay). Genomic alterations, including deleterious <i>BRCA1/2</i> alterations, genomic loss of heterozygosity (gLOH), tumor mutation burden (TMB), and microsatellite instability (MSI), were evaluated using the FoundationOne assay. HRD was defined as gLOH ≥ 16%, regardless of <i>BRCA1/2</i> mutation status. Potential associations between progression-free survival (PFS) and genomic biomarkers were evaluated using standard correlation analyses and log-rank of Kaplan–Meier estimates.</p>Results:<p>Among biomarker-evaluable samples, 22% (234/1,050) harbored <i>BRCA1/2</i> mutations and 46% (446/980) were HRD. Median TMB was low irrespective of <i>BRCA1/2</i> or HRD. Only 3% (29/1,024) had TMB ≥10 mut/Mb, and 0.3% (3/1,022) were MSI-high. PFS was better in <i>BRCA2</i>-mutated versus <i>BRCA2</i>–non-mutated tumors and in HRD versus proficient tumors. PD-L1 positivity (≥1% expression on ICs) was associated with HRD but not <i>BRCA1/2</i> mutations. PFS was not improved by adding atezolizumab in <i>BRCA2-</i>mutated or HRD tumors; there was a trend toward enhanced PFS with atezolizumab in <i>BRCA1</i>-mutated tumors.</p>Conclusions:<p>Most ovarian tumors have low TMB despite <i>BRCA1/2</i> mutations or HRD. Neither <i>BRCA1/2</i> mutation nor HRD predicted enhanced benefit from atezolizumab. This is the first randomized double-blind trial in ovarian cancer demonstrating that genomic instability triggered by <i>BRCA1/2</i> mutation or HRD is not associated with improved sensitivity to immune checkpoint inhibitors.</p><p><i><a href="https://aacrjournals.org/clincancerres/article/doi/10.1158/1078-0432.CCR-23-0048" target="_blank">See related commentary by Al-Rawi et al., p. 1645</a></i></p></div>

<div>AbstractPurpose:<p>To explore whether patients with <i>BRCA1/2</i>-mutated or homologous recombination deficient (HRD) ovarian cancers benefitted from atezolizumab in the phase III IMagyn050 (NCT03038100) trial.</p>Patients and Methods:<p>Patients with newly diagnosed ovarian cancer were randomized to either atezolizumab or placebo with standard chemotherapy and bevacizumab. Programmed death-ligand 1 (PD-L1) status of tumor-infiltrating immune cells (IC) was determined centrally (VENTANA SP142 assay). Genomic alterations, including deleterious <i>BRCA1/2</i> alterations, genomic loss of heterozygosity (gLOH), tumor mutation burden (TMB), and microsatellite instability (MSI), were evaluated using the FoundationOne assay. HRD was defined as gLOH ≥ 16%, regardless of <i>BRCA1/2</i> mutation status. Potential associations between progression-free survival (PFS) and genomic biomarkers were evaluated using standard correlation analyses and log-rank of Kaplan–Meier estimates.</p>Results:<p>Among biomarker-evaluable samples, 22% (234/1,050) harbored <i>BRCA1/2</i> mutations and 46% (446/980) were HRD. Median TMB was low irrespective of <i>BRCA1/2</i> or HRD. Only 3% (29/1,024) had TMB ≥10 mut/Mb, and 0.3% (3/1,022) were MSI-high. PFS was better in <i>BRCA2</i>-mutated versus <i>BRCA2</i>–non-mutated tumors and in HRD versus proficient tumors. PD-L1 positivity (≥1% expression on ICs) was associated with HRD but not <i>BRCA1/2</i> mutations. PFS was not improved by adding atezolizumab in <i>BRCA2-</i>mutated or HRD tumors; there was a trend toward enhanced PFS with atezolizumab in <i>BRCA1</i>-mutated tumors.</p>Conclusions:<p>Most ovarian tumors have low TMB despite <i>BRCA1/2</i> mutations or HRD. Neither <i>BRCA1/2</i> mutation nor HRD predicted enhanced benefit from atezolizumab. This is the first randomized double-blind trial in ovarian cancer demonstrating that genomic instability triggered by <i>BRCA1/2</i> mutation or HRD is not associated with improved sensitivity to immune checkpoint inhibitors.</p><p><i><a href="https://aacrjournals.org/clincancerres/article/doi/10.1158/1078-0432.CCR-23-0048" target="_blank">See related commentary by Al-Rawi et al., p. 1645</a></i></p></div>