ARID1A Mutations Research Articles

OTHR-25. ANAPLASTIC TRANSFORMATION OF DIFFUSE LEPTOMENINGEAL GLIONEURONAL TUMORS: TWO PEDIATRIC CASES

Abstract BACKGROUND Diffuse Leptomeningeal Glioneuronal Tumors (DLGT) typically have a clinical course with slow progression; however, there have been cases of anaplastic transformation. We describe the clinical presentation, radiographic features, and molecular characteristics in 2 pediatric DLGT cases that underwent aggressive transformation. METHODS Patient 1: A 20 y/o male with DLGT with BRAF-KIAA1549 fusion and loss of 1p who was first diagnosed at 2.5 y/o. Over the course of 17 years, he was treated with numerous therapies due to multiple progressions, including temozolomide, carboplatin/vincristine, selumetinib, and vinblastine. At age 17, he developed significant growth of a posterior fossa mass with solid and cystic characteristics. Resection revealed new anaplastic pathologic features. Patient 2: He was diagnosed with DLGT at age 2 y/o. Imaging demonstrated intramedullary spinal nodules at T4 and T5 with abnormal thickening and enhancement over the cerebral leptomeningeal space. A biopsy revealed DLGT with a BRAF-KIAA1549 fusion, 1p loss and Ki67 5%. He received multiple therapies including carboplatin/vincristine, vinblastine, and selumetinib. RESULTS Patient 1: Molecular characterization revealed new ATRX mutation, and CDKN2A/B homozygous deletion. Over the following 2 years, he had multiple treatments, progressions, and surgeries. Final pathology revealed significant anaplasia with Ki67 90%, ATRX loss, and mutation of PPM1D and ARID1A. He rapidly declined. Patient 2: Approximately 2.5 years after diagnosis, he developed rapid progression in the 4th and lateral ventricles. Pathology confirmed recurrent DLGT, but with high-grade transformation, H3K27M (-), H3k27m3 loss, ATRX (+), Ki67 40%. He was treated with focal irradiation followed by temozolomide/CCNU. CONCLUSION In rare cases, DLGT can undergo anaplastic transformation. Once this occurs, it behaves clinically like a high-grade glioma. Understanding the molecular underpinnings and prognostic features that lead to this transformation are important for future study.

A comparative analysis indicates SLC7A11 expression regulate the prognostic value of KEAP1-NFE2L2-CUL3 mutations in human uterine corpus endometrial carcinoma

Uterine corpus endometrial cancer (UCEC) is a third most common malignancy in women with a poor prognosis in advanced stages. In this study, we performed an integrated comparative analysis of exome and transcriptome data from The Cancer Genome Atlas (TCGA) of Lung Adenocarcinoma (LUAD), and UCEC patients. Our multi-omics analysis shows that the UCEC patients carrying mutations in the KEAP1-NFE2L2-CUL3 genes were associated with better progression-free survival (PFS), whereas the KEAP1-NFE2L2-CUL3 mutation in LUAD showed poor outcomes. Functional annotations and correlative expression studies show that genes, particularly GCLC and GCLM related to glutathione synthesis are expressed at lower levels in the KEAP1-NFE2L2-CUL3 mutant UCEC compared to LUAD. This events result in glutathione deficiency and it may compromise to combat intracellular reactive oxygen species (ROS). However, the expression of genes involved in the glutathione recycling process was not affected. On the other hand, cellular import of cystine is high due to increased SLC7A11 expression in UCEC. Because glutathione synthesis is impaired, the unconverted cysteine accumulates in cells, leading to di-sulfite stress. Apart from NRF2, ARID1A is one of the positive regulators of SLC7A11. In support, UCEC patients with co-occurrence of KEAP1-NFE2L2-CUL3 and ARID1A mutation shows significantly decreased PFS with decline of SLC7A11 expression as compared to patients carrying only KEAP1-NFE2L2-CUL3 mutation. Thus, we hypothesize that the KEAP1-NFE2L2-CUL3 mutation in UCEC leads to uncontrollable ROS with di-sulfite stress, reflecting a favorable clinical outcome.

Genome-wide DNA methylation in relation to ARID1A deficiency in ovarian clear cell carcinoma

BackgroundThe poor chemo-response and high DNA methylation of ovarian clear cell carcinoma (OCCC) have attracted extensive attentions. Recently, we revealed the mutational landscape of the human kinome and additional cancer-related genes and found deleterious mutations in ARID1A, a component of the SWI/SNF chromatin-remodeling complex, in 46% of OCCC patients. The present study aims to comprehensively investigate whether ARID1A loss and genome-wide DNA methylation are co-regulated in OCCC and identify putative therapeutic targets epigenetically regulated by ARID1A.MethodsDNA methylation of ARID1Amt/ko and ARID1Awt OCCC tumors and cell lines were analyzed by Infinium MethylationEPIC BeadChip. The clustering of OCCC tumors in relation to clinical and mutational status of tumors were analyzed by hierarchical clustering analysis of genome-wide methylation. GEO expression profiles were used to identify differentially methylated (DM) genes and their expression level in ARID1Amt/ko vs ARID1Awt OCCCs. Combining three pre-ranked GSEAs, pathways and leading-edge genes epigenetically regulated by ARID1A were revealed. The leading-edge genes that passed the in-silico validation and showed consistent ARID1A-related methylation change in tumors and cell lines were regarded as candidate genes and finally verified by bisulfite sequencing and RT-qPCR.ResultsHierarchical clustering analysis of genome-wide methylation showed two clusters of OCCC tumors. Tumor stage, ARID1A/PIK3CA mutations and TP53 mutations were significantly different between the two clusters. ARID1A mutations in OCCC did not cause global DNA methylation changes but were related to DM promoter or gene-body CpG islands of 2004 genes. Three pre-ranked GSEAs collectively revealed the significant enrichment of EZH2- and H3K27me3-related gene-sets by the ARID1A-related DM genes. 13 Leading-edge DM genes extracted from the enriched gene-sets passed the expression-based in-silico validation and showed consistent ARID1A-related methylation change in tumors and cell lines. Bisulfite sequencing and RT-qPCR analysis showed promoter hypermethylation and lower expression of IRX1, TMEM101 and TRIP6 in ARID1Amt compared to ARID1Awt OCCC cells, which was reversed by 5-aza-2′-deoxycytidine treatment.ConclusionsOur study shows that ARID1A loss is related to the differential methylation of a number of genes in OCCC. ARID1A-dependent DM genes have been identified as key genes of many cancer-related pathways that may provide new candidates for OCCC targeted treatment.

Abstract IA006: Synthetic lethalities for SWI/SNF mutant cancers

Abstract Genes that encode subunits of SWI/SNF (BAF) chromatin remodeling complexes are mutated in over 20% of cancers. These include recurrent mutations of ARID1A (BAF250a) in ovarian, endometrioid, bladder, stomach, colorectal and pancreatic cancers and neuroblastoma; of the SMARCA4 (BRG1) subunit in medulloblastomas and non-small cell lung cancers; of the PBRM1 subunit in renal carcinomas; of the ARID2 subunit in hepatocellular, lung, and pancreas carcinomas as well as melanomas; of the BRD7 subunit in breast cancers. The SWI/SNF complex includes both core and lineage-specific subunits and utilizes the energy of ATP to modulate chromatin structure and regulate transcription. My laboratory began studying the SWI/SNF complex when SMARCB1 (INI1/SNF5/BAF47) became the first SWI/SNF subunit linked to tumor suppression when it was found to be biallelically inactivated in nearly all cases of a highly aggressive type of pediatric cancer called malignant rhabdoid tumor (MRT). Despite the extremely aggressive and lethal nature of MRT we have shown that these cancers are diploid and have remarkably simple genomes. We leverage this model tumor to identify how SWI/SNF complexes function, to determine how mutation of SWI/SNF subunits drive cancer and other diseases, and to identify therapeutic vulnerabilities that result from SWI/SNF mutations. We have leverage the Cancer Dependency Map, and the Pediatric Cancer Dependencies Accelerator, to systematically identify robust and impactful synthethic lethalities resulting from SWI/SNF mutations. These mechanisms and insights will be presented. Citation Format: Charles W.M. Roberts. Synthetic lethalities for SWI/SNF mutant cancers [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Expanding and Translating Cancer Synthetic Vulnerabilities; 2024 Jun 10-13; Montreal, Quebec, Canada. Philadelphia (PA): AACR; Mol Cancer Ther 2024;23(6 Suppl):Abstract nr IA006.

Efficacy of immunotherapy in ARID1A-mutant solid tumors: a single-center retrospective study

BackgroundImmune checkpoint inhibitors (ICIs), especially those targeting programmed cell death-1 (PD-1) and programmed cell death ligand-1 (PD-L1), have introduced a new treatment landscape for many types of tumors. However, they only achieve a limited therapeutic response. Hence, identifying patients who may benefit from ICIs is currently a challenge.Methods47 tumor patients harboring ARID1A mutations were retrospectively studied. The genomic profiling data through next-generation sequencing (NGS) and relevant clinical information were collected and analyzed. Additionally, bioinformatics analysis of the expression of immune checkpoints and immune cell infiltration levels was conducted in ARID1A-mutant gastric cancer (GC).ResultsARID1A mutations frequently co-occur with mutations in DNA damage repair (DDR)-associated genes. Among the 35 ARID1A-mutant patients who received immunotherapy, 27 were evaluable., with the objective response rate (ORR) was 48.15% (13/27), and the disease control rate (DCR) was 92.59% (25/27). Moreover, survival assays revealed that ARID1A-mutant patients had longer median overall survival (mOS) after immunotherapy. In ARID1A-mutated GC patients, receiving ICIs treatment indicated longer progressive-free survival (PFS). Additionally, the incidence of microsatellite instability-high (MSI-H), high tumor mutation burden (TMB-H) and Epstein‒Barr virus (EBV) infection was elevated. Bioinformatic analysis showed significant enrichment of immune response and T cell activation pathway within differentially expressed genes in ARID1A-mutant GC group. Finally, ARID1A mutations status was considered to be highly correlated with the level of tumor infiltrating lymphocytes (TILs) and high expression of immune checkpoints.ConclusionsPatients with tumors harboring ARID1A mutations may achieve better clinical outcomes from immunotherapy, especially in GC. ARID1A mutations can lead to genomic instability and reshape the tumor immune microenvironment (TIME), which can be used as a biomarker for immunotherapy.

Serial Cell-Free DNA Sequencing in ROS1 Fusion-Positive Lung Cancers During Treatment With Entrectinib.

Patients with metastatic ROS1 fusion-positive non-small cell lung cancer (NSCLC) are effectively treated with entrectinib, a multikinase inhibitor. Whether serial targeted gene panel sequencing of cell-free DNA (cfDNA) can identify response and progression along with mechanisms of acquired resistance to entrectinib is underexplored. In patients with ROS1 fusion-positive NSCLC, coclinical trial plasma samples were collected before treatment, after two cycles, and after progression on entrectinib (global phase II clinical trial, ClinicalTrials.gov identifier: NCT02568267). Samples underwent cfDNA analysis using MSK-ACCESS. Variant allele frequencies of detectable alterations were correlated with objective response per RECIST v1.1 criteria. Twelve patients were included, with best response as partial response (n = 9, 75%), stable disease (n = 2, 17%), and progressive disease (PD; n = 1, 8%). A ROS1 fusion was variably detected in cfDNA; however, patients without a ROS1 fusion in cfDNA had no other somatic alterations detected, indicative of possible low cfDNA shedding. Clearance of the enrolling ROS1 fusion or concurrent non-ROS1 alterations (TP53, CDH1, NF1, or ARID1A mutations) was observed in response to entrectinib therapy. Radiologic PD was accompanied by redemonstration of a ROS1 fusion or non-ROS1 alterations. On-target resistance was rare; only one patient acquired ROS1 G2032R at the time of progression. Several patients acquired new off-target likely oncogenic alterations, including a truncating alteration in NF1. Serial cfDNA monitoring may complement radiographic assessments as determinants of response and resistance to entrectinib in ROS1 fusion-positive lung cancers in addition to detecting putative resistance mechanisms on progression.

Association of chr11q13 amplification with survival and recurrence in patients with surgically treated hepatocellular carcinoma.

e16253 Background: Hepatocellular carcinoma (HCC) is a highly lethal and aggressive malignant tumor characterized by high rates of recurrence and metastasis, and low survival outcomes. The current treatments available for HCC have shown limited success, and the prevalence of genomic characterization and their association with survival and recurrence in HCC patients are largely unknown. Methods: The investigation enrolled 1,221 Chinese individuals diagnosed with primary HCC. This study collected samples including tumor and paired tumor-free tissues and clinical characteristics. Among them, 348 patients' clinical outcome data, including overall survival (OS) and recurrence-free survival (RFS) were gathered. Genomic analysis was conducted through panel sequencing by OrigiMed. Hazard ratios were calculated employing both univariate and multivariate Cox proportional hazards regression models. The log-rank test and Kaplan-Meier plots were used to assess comparison of clinical outcomes by various prognostic factors. For other statistical analyses, a two-tailed unpaired t-test and Fisher's exact test were applied. Results: With a median age of 54, 87% of the cases were male. Pertaining to risk factors, 74% cases had HBV infection and 62% cases were cirrhosis. Meanwhile, serum AFP levels greater (or less) than 400 ng/mL were present in 299 cases (or 485 cases). Panel sequencing identified the most prevalent mutations ( > 10%, excluding copy number variations) in TP53 (60%), TERT (40%), CTNNB1 (21%), AXIN1 (14%), LRP1B (14%), ARID1A (13%), RB1 (12%) and TSC2 (11%). The most frequently amplified genes were located at chr11q13, including CCND1 (9%), FGF19 (9%), FGF4 (7%) and FGF3 (7%). Survival analysis indicated that patients with Chr11q13 amp had significantly shorter OS and RFS. Further studies revealed a higher incidence of Chr11q13 amp in patients at advanced stages III/IV (64/564, 11%) compared to early-stage I/II (38/523, 7%), and in patients with vascular invasion (31/220, 14%) versus those without (44/599, 7%). No significant differences were observed in tumor mutational burden and HLA-I evolutionary divergence between patients with various Chr11q13 amp statuses. Furthermore, multivariate Cox proportional hazards regression models were utilized to examine the relationship between Chr11q13 amp status, characteristics and outcomes. Among the 248 patients with comprehensive clinical characteristics and available OS and RFS data, analyses indicated significant negative correlations between Chr11q13 amp and embolus with both OS and RFS. Conclusions: Our study elucidates that the presence of Chr11q13 amp was significantly associated with worse survival and increased risk of recurrence among a large cohort of Chinese patients with HCC. This discovery yields important insights into the understanding of HCC and has the potential to benefit personalized therapy.

Efficacy, safety, and predictive biomarkers of dalpiciclib combined with letrozole, pertuzumab and trastuzumab as neoadjuvant therapy in HR+/HER2+ breast cancer: A phase II study.

e12621 Background: HR+/HER2+ breast cancer is a unique subtype of breast cancer. Between ER and HER2 crosstalk pathways may affect the sensitivity to both HER2-targeted and endocrine therapy in patients with HR+/HER2+ breast cancer. Current therapies for HER2-positive breast cancer have demonstrated limited efficacy in patients with HR+/HER2+ breast cancer. This Phase II trial aimed to assess the efficacy and safety of a neoadjuvant regimen combining trastuzumab, pertuzumab, dalpiciclib (a cyclin dependent kinase 4/6 inhibitor) and letrozole in patients with HR+/HER2+ breast cancer, alongside the exploration of efficacy biomarkers. Methods: Patients were administered six 28-day cycles of dalpiciclib (150 mg once daily on days 1-21) and letrozole (2.5 mg once daily), plus six 21-day cycles of trastuzumab (8 mg/kg loading dose followed by 6 mg/kg maintenance dose on day 1), pertuzumab (840mg loading dose followed by 420mg maintenance dose on day 1), prior to surgery. The primary endpoint was total pathological complete response (tpCR, ypT0/is, ypN0) rate. Secondary endpoints were objective response rate (ORR), breast pathological complete response (bpCR; ypT0/is) rate, change in Ki-67 level from baseline to one cycle of treatment and to surgery, and safety. For biomarkers analysis, next-generation sequencing was performed on pre-treatment tissue and circulating tumor DNA (ctDNA) at various time points before surgery. Results: A total of 14 patients who completed the neoadjuvant treatment and surgery between July 12, 2022 and August 12, 2023 were enrolled. A 50.0% (7 out of 14) tpCR and bpCR rate was observed, with an ORR of 92.9%. Significant reductions in Ki-67 levels were noted after both one ( P<0.05) and six cycles of neoadjuvant therapy ( P<0.05). Grade 4 neutropenia was reported in one case, with no fatalities. The most common grade 3 adverse events were neutropenia (10 [71.4%]) and leukopenia (8 [57.1%]). NGS identified frequent mutations in TP53 (84.6%), PIK3CA (53.8%), and ARID1A (30.8%). Cell cycle pathway gene alterations correlated with a higher pCR rate (80% vs 25%, P=0.103). Eight (61.5%) patients had positive ctDNA at baseline, and ctDNA positivity decreased significantly post-neoadjuvant treatment ( P<0.05). Patients with positive ctDNA at baseline without clearance post-treatment exhibited a trend towards a lower pCR rate. Conclusions: This combination neoadjuvant regimen of dalpiciclib, letrozole, pertuzumab and trastuzumab demonstrated promising pathological responses and manageable safety in patients with HR+/HER2+ breast cancer. The predictive value of genetic alterations and ctDNA status for treatment efficacy warrants further investigation. Clinical trial information: ChiCTR2200062114.

Characterization of TP53 mutations in actionable driver-negative non-small cell lung cancer (NSCLC).

8621 Background: TP53 mutations are common in NSCLC and have been associated with poor prognosis in patients with actionable genomic drivers. Despite the increased prevalence in actionable driver-negative (DN) NSCLC, the role of TP53 mutations in this subtype is not fully explored. We characterize the association of TP53 mutations with the molecular and immune landscapes, as well as outcomes, in DN NSCLC histologic subtypes. Methods: 17,689 NSCLC specimens were analyzed using next-generation sequencing of DNA (DNA-592 panel or whole exome) or RNA (whole transcriptome) at Caris Life Sciences (Phoenix, AZ). Tumors with KRAS, EGFR, BRAF, MET, HER2, ALK, ROS1, NRG1, and NTRK 1-3 alterations were excluded. Specimens were grouped as TP53WT (wild type) or TP53MUT (pathogenic/likely pathogenic mutations). PD-L1 expression was analyzed by IHC (Dako 22c3; PD-L1 positive: TPS ≥1%). TMB was measured by counting all somatic mutations found per tumor (TMB-H: ≥10 mutations/Mb). Composition of the tumor microenvironment (TME) was estimated from bulk RNA sequencing using QuanTIseq method. Overall survival was extracted from insurance claims data and calculated from the time of tissue collection (OS) or initiation of Pembrolizumab treatment (Pembro-OS) to the last contact, using Kaplan-Meier estimates. Significance was determined using chi-square, Fisher’s Exact, Mann Whitney U and adjusted for multiple comparisons (p-value < 0.05). Results: Among DN tumors, the prevalence of TP53MUT was 86%. TP53MUT was more common in men (62% vs 38%), those with a smoking history (99% vs 1%), and those with squamous cell histology (46% vs33.6%, all p<0.05). Interestingly, histological stratification suggested that TP53MUT was associated with poor OS in adenocarcinoma (AC) (HR:1.3, p<0.05), and shorter Pembro-OS in squamous cell carcinoma (SCC) (HR:1.425, p<0.05). In AC, mutations in FAT1, ARID1A, SMARCA4, ARID2 and RBM10 were enriched, while in SCC, mutations in PIK3CA were less common with TP53MUT. Gene sets involved in cell cycle regulation such as G2M, MYC, and E2F targets were enriched in TP53MUT and to a greater extent in AC (1.22-1.29) vs SCC (1.06-1.08, both p<0.05). Looking at immunotherapy-related biomarkers, both AC and SCC TP53MUT tumors had a higher prevalence of TMB-H compared to TP53WT, while PD-L1 positivity was enriched in only AC TP53MUT tumors. Conversely, KEAP1 and STK11 mutations were enriched in AC TP53WT. M2 Macrophage (1.25-fold) and NK cell (1.3-fold) fractions were enriched and B cell fractions (1.25-fold) were less common in TP53MUT SCC TMEs (all p<0.05). Conclusions: TP53MUT were associated with poor OS and Pembro-OS exclusively in AC and SCC, respectively. The distinct molecular and immune landscapes associated with TP53MUT in AC and SCC potentially explain the differences in outcomes mentioned above. Further research is needed to better understand therapeutic implications of TP53 mutations in DN-NSCLC.

An exploratory analysis of the genetic alteration associated with early-onset gastric and colorectal cancer using a large-scale nationwide database of Japan (C-CAT).

4058 Background: The recent global concern about the early onset cancer (EOC) has been rising in the field of GI cancers. Precision oncology based on comprehensive genome profile (CGP) test is anticipated to attribute the improvement of cancer treatment for EOC. This study explored the genetic alteration of EOC and association with genome matched therapy in colorectal cancer (CRC) and gastric or gastroesophageal junction cancer (G/GEJC). Methods: We retrospectively assessed Japanese nationwide, the Center for Cancer Genomics and Advanced Therapeutics (C-CAT) database. Pts meets following eligibility criteria were enrolled. 1) Pts received the reimbursed CGP tests between June 2019 and May 2023 in Japan, 2) pts registered as CRC or G/GEJC, 3) pts agreed with the utilization of their data. We defined EOC as diagnosed at less than 50 and 40 in EO-CRC and EO-G/GEJC, respectively. We investigated the genomic alterations of EOC and compared the genes with a difference in frequency of 5% or more between earlier and later onset cancer of disease. The transition rate to the subsequent matched therapy was compared between EOC and non-EOC. This study was approved by both the ethics committee of Cancer Institute Hospital of JFCR (No. 2022-GB-121) and C-CAT data utilization review board (No. AP20230309-01N). Results: Among a total of 8,180 eligible pts, 1,289 (19.9%) and 123 (7.2%) EOC were identified in CRC and G/GEJC, respectively. Tissue based assay with Foundation One (n = 6.591, 80.6%) was most frequently employed as CGP test. TP53 (84.1%), APC (77.2%) and KRAS (49.5%) mutation were most frequently occurred in EO CRC. Meanwhile, TP53 (64.2%), CDH1 (36.5%) and ARID1A (17.1%) mutation were the most prevalent in EO G/GEJC. Among the top 30th somatically mutated genes in EO CRC and EO G/GEJC, 31 (96.9%) and 29 (85.3%) genes shared with non-EO in CRC and G/GEJC, respectively. Notably, the proportion of shared genes was significantly decline to 21 (71.9%) and 18 (52.9%) in CRC and G/GEJC when they compared between pts aged <30 and ≥30 years old. The proportion of pts harboring at least one actionable mutation was 42.3% in EO CRC similar to that of non-EO CRC (43.2%) and 19.5% in EO G/GEJC and lower than that of non-EO G/GEJC (32.2%), respectively. The proportions of individuals who received targeted therapy as recommended by CGP test were all approximately 5% (EOC vs. non-EOC: 6.4% vs. 5.6% in CRC and 4.1% vs. 4.4% in G/GEJC). The treatment access rate was not improved in very young pts (aged <30). Conclusions: Genomic alterations were mostly shared between EOC and non-EOC in pts with CRC and G/GEJC. The mutation profile apparently differs between earlier onset (<30) and later onset (≥30) both in CRC and G/GEJC. Very limited proportion of EOC could access the matched therapy after CGP test in the treatment of CRC and G/GEJC as well as non-EOC.

ARID1A Mutations in Gastric Cancer: A Review with Focus on Clinicopathological Features, Molecular Background and Diagnostic Interpretation.

AT-rich interaction domain 1 (ARID1A) is a pivotal gene with a significant role in gastrointestinal tumors which encodes a protein referred to as BAF250a or SMARCF1, an integral component of the SWI/SNF (SWItch/sucrose non-fermentable) chromatin remodeling complex. This complex is instrumental in regulating gene expression by modifying the structure of chromatin to affect the accessibility of DNA. Mutations in ARID1A have been identified in various gastrointestinal cancers, including colorectal, gastric, and pancreatic cancers. These mutations have the potential to disrupt normal SWI/SNF complex function, resulting in aberrant gene expression and potentially contributing to the initiation and progression of these malignancies. ARID1A mutations are relatively common in gastric cancer, particularly in specific adenocarcinoma subtypes. Moreover, such mutations are more frequently observed in specific molecular subtypes, such as microsatellite stable (MSS) cancers and those with a diffuse histological subtype. Understanding the presence and implications of ARID1A mutations in GC is of paramount importance for tailoring personalized treatment strategies and assessing prognosis, particularly given their potential in predicting patient response to novel treatment strategies including immunotherapy, poly(ADP) ribose polymerase (PARP) inhibitors, mammalian target of rapamycin (mTOR) inhibitors, and enhancer of zeste 2 polycomb repressive complex 2 subunit (EZH2) inhibitors.

Durable pembrolizumab response in metastatic MSS ARID1A-mutant undifferentiated carcinoma of the esophagus.

In 2021, the FDA approved the combination of pembrolizumab with platinum and fluoropyrimidine-based chemotherapy for advanced esophageal and gastroesophageal junction (GEJ) cancers, regardless of the PD-L1 score. Pembrolizumab alone may benefit MSI-H gastroesophageal adenocarcinomas, but most patients with pMMR/MSS types require it in combination with standard chemotherapy. The NCCN recognizes the predictive value of PD-L1 CPS and recommends pembrolizumab plus chemotherapy for PD-L1 CPS ≥10. Undifferentiated carcinoma of the esophagus, a rare esophageal cancer subtype with a poor prognosis, still lacks a well-defined optimal treatment. We report a case of an 87-year-old female with advanced, pMMR/MSS, HER2-negative, ARID1A-mutant, undifferentiated carcinoma of the esophagus with a PD-L1 CPS of 20, who has shown a durable ongoing response to pembrolizumab monotherapy for 2 years now. The case highlights a favorable response, possibly attributed to the high CPS score combined with the ARID1A mutation, as recent research suggests that ARID1A mutations may increase immunotherapy susceptibility.

ARID1A suppresses R-loop-mediated STING-type I interferon pathway activation of anti-tumor immunity

Clinical trials have identified ARID1A mutations as enriched among patients who respond favorably to immune checkpoint blockade (ICB) in several solid tumor types independent of microsatellite instability. We show that ARID1A loss in murine models is sufficient to induce anti-tumor immune phenotypes observed in ARID1A mutant human cancers, including increased CD8+ Tcell infiltration and cytolytic activity. ARID1A-deficient cancers upregulated an interferon (IFN) gene expression signature, the ARID1A-IFN signature, associated with increased R-loops and cytosolic single-stranded DNA (ssDNA). Overexpression of the R-loop resolving enzyme, RNASEH2B, or cytosolic DNase, TREX1, in ARID1A-deficient cells prevented cytosolic ssDNA accumulation and ARID1A-IFN gene upregulation. Further, the ARID1A-IFN signature and anti-tumor immunity were driven by STING-dependent type I IFN signaling, which was required for improved responsiveness of ARID1A mutant tumors to ICB treatment. These findings define a molecular mechanism underlying anti-tumor immunity in ARID1A mutant cancers.

Molecular characteristics of early-onset compared with late-onset colorectal cancer: a case controlled study.

Early-onset colorectal cancer (EOCRC) is associated with a poorer prognosis relative to late-onset colorectal cancer (LOCRC), and its incidence has witnessed a gradual escalation in recent years. This necessitates a comprehensive examination of the underlying pathogenesis and the identification of therapeutic targets specific to EOCRC patients. The present study aimed to delineate the distinct molecular landscape of EOCRC by juxtaposing it with that of LOCRC. A total of 11344 colorectal cancer patients, diagnosed between 2003 and 2022, were enrolled in this study, comprising 578 EOCRC cases and 10766 LOCRC cases. Next-generation sequencing technology was employed to assess the tumor-related mutation and tumor mutation burden (TMB) in these patients. PD-L1 expression was quantified using immunohistochemistry. Microsatellite instability (MSI) was determined via capillary electrophoresis (2B3D NCI Panel). Upon comparing LOCRC with EOCRC patients, the latter group demonstrated a tendency towards advanced TNM stage, lower tumor differentiation, and less favorable histological types. Among LOCRC patients, those with MSI-H status were found to have an earlier TNM stage compared to those with MSI-L/MSS status. Significantly, the incidence of MSI-H was notably higher in EOCRC (10.2%) compared to LOCRC (2.2%). Mutations in the 7-gene panel (ARID1A, FANCI, CASP8, DGFRA, DPYD, TSHR, and PRKCI) were more prevalent in LOCRC. Within the EOCRC cohort, patients with the MSI-H subtype displayed an earlier TNM stage but concurrently exhibited poorer tissue differentiation and a higher frequency of mucinous adenocarcinoma. Among EOCRC patients, FBXW7, FAT1, ATM, ARID1A, and KMT2B mutations were significantly enriched in the MSI-H subgroup. A comparative analysis of MSI-H patients revealed heightened mutation frequencies of FGFBR2, PBRM1, RNF43, LRP1B, FBXW7, ATM, and ARID1A in the EOCRC group. Furthermore, EOCRC patients demonstrated a higher overall TMB, particularly in the MSI-H subtype. PD-L1 expression was elevated in EOCRC and positively associated with MSI status. This study revealed a significantly higher MSI-H distribution rate in EOCRC, and EOCRC exhibits a distinct mutational signature coupled with higher PD-L1 expression. These findings hold promise in guiding personalized therapeutic strategies for improved disease management in EOCRC patients.

ARID1A in Gynecologic Precancers and Cancers.

The highest frequency of genetic alterations in the tumor suppressor ARID1A occurs in malignancies of the female reproductive tract. The prevalence of ARID1A alterations in gynecologic precancers and cancers is summarized from the literature, and the putative mechanisms of tumor suppressive action examined both in benign/precursor lesions including endometriosis and atypical hyperplasia and in malignancies of the ovary, uterus, cervix and vagina. ARID1A alterations in gynecologic cancers are usually loss-of-function mutations, resulting in diminished or absent protein expression. ARID1A deficiency results in pleiotropic downstream effects related not only to its role in transcriptional regulation as a SWI/SNF complex subunit, but also related to the functions of ARID1A in DNA replication and repair, immune modulation, cell cycle progression, endoplasmic reticulum (ER) stress and oxidative stress. The most promising actionable signaling pathway interactions and therapeutic vulnerabilities of ARID1A mutated cancers are presented with a critical review of the currently available experimental and clinical evidence. The role of ARID1A in response to chemotherapeutic agents, radiation therapy and immunotherapy is also addressed. In summary, the multi-faceted role of ARID1A mutation in precancer and cancer is examined through a clinical lens focused on development of novel preventive and therapeutic interventions for gynecological cancers.

MITO END-3: efficacy of avelumab immunotherapy according to molecular profiling in first-line endometrial cancer therapy

Immunotherapy combined with chemotherapy significantly improves progression-free survival (PFS) compared to first-line chemotherapy alone in advanced endometrial cancer (EC), with a much larger effect size in microsatellite instability-high (MSI-H) cases. New biomarkers might help to select patients who may have benefit among those with a microsatellite-stable (MSS) tumor. In a pre-planned translational analysis of the MITO END-3 trial, we assessed the significance of genomic abnormalities in patients randomized to standard carboplatin/paclitaxel without or with avelumab. Out of 125 randomized patients, 109 had samples eligible for next-generation sequencing analysis, and 102 had MSI tested. According to The Cancer Genome Atlas (TCGA), there were 29 cases with MSI-H, 26 with MSS TP53 wild type (wt), 47 with MSS TP53 mutated (mut), and 1 case with POLE mutation. Four mutated genes were present in >30% of cases: TP53, PIK3CA, ARID1A, and PTEN. Eleven patients (10%) had a BRCA1/2 mutation (five in MSI-H and six in MSS). High tumor mutational burden (≥10 muts/Mb) was observed in all MSI-H patients, in 4 out of 47 MSS/TP53 mut, and no case in the MSS/TP53 wt category. The effect of avelumab on PFS significantly varied according to TCGA categories, being favorable in MSI-H and worst in MSS/TP53 mut (P interaction= 0.003); a similar non-significant trend was seen in survival analysis. ARID1A and PTEN also showed a statistically significant interaction with treatment effect, which was better in the presence of the mutation (ARID1A P interaction= 0.01; PTEN P interaction= 0.002). The MITO END-3 trial results suggest that TP53 mutation is associated with a poor effect of avelumab, while mutations of PTEN and ARID1A are related to a positive effect of the drug in patients with advanced EC.

MRNA Display Identifies Potent, Paralog-Selective Peptidic Ligands for ARID1B.

The ARID1A and ARID1B subunits are mutually exclusive components of the BAF variant of SWI/SNF chromatin remodeling complexes. Loss of function mutations in ARID1A are frequently observed in various cancers, resulting in a dependency on the paralog ARID1B for cancer cell proliferation. However, ARID1B has never been targeted directly, and the high degree of sequence similarity to ARID1A poses a challenge for the development of selective binders. In this study, we used mRNA display to identify peptidic ligands that bind with nanomolar affinities to ARID1B and showed high selectivity over ARID1A. Using orthogonal biochemical, biophysical, and chemical biology tools, we demonstrate that the peptides engage two different binding pockets, one of which directly involves an ARID1B-exclusive cysteine that could allow covalent targeting by small molecules. Our findings impart the first evidence of the ligandability of ARID1B, provide valuable tools for drug discovery, and suggest opportunities for the development of selective molecules to exploit the synthetic lethal relationship between ARID1A and ARID1B in cancer.

Recent Advances in Pathology of Intrahepatic Cholangiocarcinoma.

Intrahepatic cholangiocarcinoma (ICCA) is a malignant epithelial neoplasm characterized by biliary differentiation within the liver. ICCA is molecularly heterogeneous and exhibits a broad spectrum of histopathological features. It is a highly aggressive carcinoma with high mortality and poor survival rates. ICCAs are classified into two main subtypes: the small-duct type and large-duct types. These two tumor types have different cell origins and clinicopathological features. ICCAs are characterized by numerous molecular alterations, including mutations in KRAS, TP53, IDH1/2, ARID1A, BAP1, BRAF, SAMD4, and EGFR, and FGFR2 fusion. Two main molecular subtypes-inflammation and proliferation-have been proposed. Recent advances in high-throughput assays using next-generation sequencing have improved our understanding of ICCA pathogenesis and molecular genetics. The diagnosis of ICCA poses a significant challenge for pathologists because of its varied morphologies and phenotypes. Accurate diagnosis of ICCA is essential for effective patient management and prognostic determination. This article provides an updated overview of ICCA pathology, focusing particularly on molecular features, histological subtypes, and diagnostic approaches.

Abstract LB373: Pilot whole-exome sequencing data of formalin-fixed paraffin embedded endometrial tumors in the Epidemiology of Endometrial Cancer Consortium (E2C2)

Abstract Background: Endometrial cancer (EC) is the most common gynecologic cancer in the U.S.: incidence and mortality are rising. Black women face 2-fold higher mortality compared with other racial groups. To understand the role of tumor biology underlying these health inequities, we are sequencing the tumor exomes of 1,000 Black and 2,000 non-Black women in the Epidemiology of Endometrial Cancer Consortium. To inform this effort, we have completed whole-exome tumor sequencing in 35 EC patients. We present early sample performance and mutational insights of this pilot. Methods: We extracted DNA from formalin-fixed paraffin-embedded (FFPE) tumor tissues (cores, scroll) and matched normal specimens (blood, tissue) from 35 women diagnosed with EC in the Louisiana Tumor Registry, Nurses’ Health Study, and Polish Endometrial Cancer Study. Whole-exome sequencing was conducted by the Center for Inherited Disease Research at Johns Hopkins University, which called somatic alterations using matched normal samples as the germline profile (NovaSeq6000). We excluded two contaminated core samples and one paired scroll with extremely low coverage, leaving 33 women in our analytic sample. We examined the mutational landscape of EC overall and separately in 7 Black and 26 non-Black patients. For 23 women, we obtained both an FFPE scroll of the full block and FFPE tumor cores enabling a direct comparative analysis of DNA extraction yield and sequencing performance by sample source. We ran a published allele-specific copy number and clonal heterogeneity analysis tool (FACETS) in these 23 women to calculate tumor purity by tissue type. Results: Results from our pilot study revealed the most frequently mutated genes in our pilot population were PTEN (61%), ARID1A (48%), and PIK3CA (39%). We observed similar mutation frequencies for PIK3CA in both non-Black and Black women (38% vs 43%). TP53 was more frequently mutated in Black women (57% vs 16%), while ARID1A mutation was more common in non-Black women (58% vs 14%). 10 (30%) patient samples had chromosome 10 copy-neutral loss of heterozygosity. Of these, 8 (80%) had PTEN bi-allelic alterations. Of participants with both core and scroll tissue available, both sample types were successfully sequenced, although cores showed modestly better performance: 74% of core samples (vs 26% for scrolls) had a higher percentage of bases read at a target depth of 100x, and the median tumor purity for cores estimated using FACETS was higher than scrolls (53% vs 42%). Tumor purity could not be calculated for seven tissue samples due to either tumor diploidy or purity being too low: of these samples the majority were scrolls (86%). We observed greater concordance between core and scroll variant allele frequency when tumor purity was ≥30%: the benefits of cores vs scrolls matter at lower tumor purity. ConclusionsIn line with TCGA data, these pilot findings suggest potential differences in tumor mutational landscape by race and we will be interrogating these in our larger study population. FFPE core tissue generally performed better than FFPE scroll tissue in whole-exome sequencing, but our data suggest scrolls remain a viable option for sequencing when cores are unavailable. This has the potential to offer valuable insight for conducting population-based next-generation studies, which mostly rely on FFPE-derived tissues. Citation Format: Noah C. Peeri, Megan A. Clarke, Immaculata De Vivo, Mengmeng Du, Lucio Miele, Jeffin Naduparambil, Kathryn L. Penney, Venkat Seshan, Ronglai Shen, Veronica W. Setiawan, Nicolas Wentzensen, Xiao-Cheng Wu, Arnold Zea, Wenyu Zhang. Pilot whole-exome sequencing data of formalin-fixed paraffin embedded endometrial tumors in the Epidemiology of Endometrial Cancer Consortium (E2C2) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB373.

Abstract LB231: The mutagenic forces shaping the genomic landscape of lung cancer in never smokers

Abstract While most lung cancers are associated with tobacco smoking, prior studies have indicated that 15-20% of cases are found in never smokers. Lung cancer in never smokers (LCINS) shows demographic variations, being more common in females and Asian populations. Epidemiological studies have also identified environmental risk factors for LCINS, including exposure to secondhand tobacco smoke and air pollution. As part of the Sherlock-Lung project (current data freeze of 1217 samples), we generated deep WGS data from a large international cohort of 871 treatment-naïve LCINS recruited from 28 locations across four continents. Our cohort allowed mapping the genomic landscape operative in lung cancer histologies commonly found in never smokers, including adenocarcinomas (n=737) and carcinoids (n=61), as well as other histologies rarely attributed to never smokers (n=73). Information on passive smoking was collected for 458 patients, with 250 being exposed to secondhand smoke. We identified driver alterations and performed mutational signature analyses for single base substitutions (SBS), indels, doublet base substitutions (DBS), copy number alterations, and structural variants. We detected eighteen SBS signatures, with eight not previously linked to LCINS, including SBS4, associated with smoking but also observed in lifelong non-smokers exposed to different environmental mutagens, such as indoor pollution. Several additional signatures were detected in other variant types, including a novel indel signature. Notably, secondhand smoke exposure corresponded to increased SBS burden, although it was not associated with specific signatures. In contrast, we observed a signature-specific association of air pollution (measured as PM2.5 exposure) with SBS, indel, and DBS burden. SBS4 and correlated signatures ID3 and DBS2 were positively associated with PM2.5 exposure. Similarly, clock-like signature SBS5 was highly correlated with PM2.5, potentially acting as a readout of a promotion mechanism where lung cells undergo more cell divisions in individuals living in highly polluted areas. We also observed variability across histologies and ancestries for signatures and driver mutations, including enrichment of signatures SBS17b and SBS40a as well as KRAS mutations in adenocarcinomas from Europeans; aristolochic-acid associated signature SBS22a, and EGFR and TP53 mutations in adenocarcinomas from East Asians; and signature SBS8 and ARID1A mutations in carcinoids from Europeans. The unprecedented size of our cohort allowed us to refine the prevalence and intensity of the driver mutations and mutational signatures involved in LCINS, as well as their variability across ancestries, geographical locations, and histologies. Our results indicate that air pollution may act as both initiator and promoter of neoplastic expansion of LCINS. Citation Format: Marcos Diaz-Gay, Tongwu Zhang, Azhar Khandekar, Burçak Otlu, Shuvro Nandi, Christopher D. Steele, Nathaniel Rothman, Stephen J. Chanock, Qing Lan, Ludmil B. Alexandrov, Maria Teresa Landi. The mutagenic forces shaping the genomic landscape of lung cancer in never smokers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB231.