Low Variant Allele Frequency Research Articles

Defining the transcriptome of PIK3CA-altered cells in a human capillary malformation using single cell long-read sequencing

PIK3CA-related overgrowth spectrum (PROS) disorders are caused by somatic mosaic variants that result in constitutive activation of the phosphatidylinositol-3-kinase/AKT/mTOR pathway. Promising responses to molecularly targeted therapy have been reported, although identification of an appropriate agent can be hampered by the mosaic nature and corresponding low variant allele frequency of the causal variant. Moreover, our understanding of the molecular consequences of these variants—for example how they affect gene expression profiles—remains limited. Here we describe in vitro expansion of a human capillary malformation followed by molecular characterization using exome sequencing, single cell gene expression, and targeted long-read single cell RNA-sequencing in a patient with clinical features consistent with Megalencephaly-Capillary Malformation Syndrome (MCAP, a PROS condition). These approaches identified a targetable PIK3CA variant with expression restricted to PAX3+ fibroblast and undifferentiated keratinocyte populations. This study highlights the innovative combination of next-generation single cell sequencing methods to better understand unique transcriptomic profiles and cell types associated with MCAP, revealing molecular intricacies of this genetic syndrome.

Activating STAT3 mutations in CD8+ T-cells correlate to serological positivity in rheumatoid arthritis

ObjectivesLarge granular lymphocyte (LGL) leukemia is a rare hematologic malignancy characterized by clonal expansion of cytotoxic T-cells frequent somatic activating STAT3 mutations. Based on the disease overlap between LGL leukemia rheumatoid arthritis (RA)a putative role for CD8+ T-cells in RA we hypothesized that STAT3 mutations may be detected in RA patient CD8+ T-cells correlate with clinical characteristics.MethodsBlood samples, clinical parameters, and demographics were collected from 98 RA patients and 9 healthy controls (HCs). CD8+ cell DNA was isolated and analyzed via droplet digital (dd)PCR to detect STAT3 mutations common in LGL leukemia: Y640F, D661Y, and the S614 to G618 region. STAT3 data from 99 HCs from a public dataset supplemented our 9 HCs.ResultsRA patients had significantly increased presence of STAT3 mutations compared to controls (Y640F p=0.0005, D661Y p=0.0005). The majority of these were low variant allele frequency (VAF) (0.008-0.05%) mutations detected in a higher proportion of the RA population (31/98 Y640F, 17/98 D661Y) vs. HCs (0/108 Y640F, 0/108 D661Y). In addition, 3/98 RA patients had a STAT3 mutation at a VAF >5% compared to 0/108 controls. Serological markers, RF and anti-CCP positivity, were more frequently positive in RA patients with STAT3 mutation relative to those without (88% vs 59% RF, p=0.047; 92% vs 58% anti-CCP, p=0.031, respectively).ConclusionsSTAT3 activating mutations were detected in RA patient CD8+ cells and associated with seropositivity. Thus, STAT3 activating mutations may play a role in disease pathogenesis in a subset of RA patients.

Nivolumab plus anlotinib hydrochloride in advanced gastric adenocarcinoma and esophageal squamous cell carcinoma: the phase II OASIS trial

Vascular endothelial growth factor inhibitors, including tyrosine kinase inhibitors (TKIs), possess immunomodulatory properties and have shown promising outcomes when combined with anti-PD-1 antibodies. The OASIS phase II trial (NCT04503967) is designed to determine the clinical activity and safety of nivolumab (anti-PD-1) and anlotinib hydrochloride (a multi-targets TKI) as second-line or above therapy in patients with advanced gastric adenocarcinoma (GAC) and esophageal squamous cell carcinoma (ESCC). From December 2020 to September 2022, 45 patients with GAC and 3 with ESCC were enrolled in this study. The pre-specified endpoints were reached, with the primary endpoint of overall response rate achieving 29.2%. For secondary objectives, disease control rate was 64.6%; median progression-free survival was 4.0 months; and median overall survival was 11.1 months with a manageable toxicity profile. The exploratory analyses unveiled that the balance of gut bacteria and the presence of a pre-existing immune signature characterized by a high percentage of CD68+PD-L1+ PD-1+ macrophages and low pretreatment variant allele frequencies (VAF), as well as low expression of certain cytokines were significantly associated with improved clinical outcomes in patients with GAC.

Detection of KIT Mutations in Systemic Mastocytosis: How, When, and Why.

More than 90% of patients affected by mastocytosis are characterized by a somatic point mutation of KIT, which induces ligand-independent activation of the receptor and downstream signal triggering, ultimately leading to mast cell accumulation and survival. The most frequent mutation is KIT p.D816V, but other rarer mutations can also be found. These mutations often have a very low variant allele frequency (VAF), well below the sensitivity of common next-generation sequencing (NGS) methods used in routine diagnostic panels. Highly sensitive methods are developing for detecting mutations. This review summarizes the current indications on the recommended methods and on how to manage and interpret molecular data for the diagnosis and follow-up of patients with mastocytosis.

DdPCR Overcomes the CRISPR-Cas13a-Based Technique for the Detection of the BRAF p.V600E Mutation in Liquid Biopsies.

The isolation of circulating tumoral DNA (ctDNA) present in the bloodstream brings about the opportunity to detect genomic aberrations from the tumor of origin. However, the low amounts of ctDNA present in liquid biopsy samples makes the development of highly sensitive techniques necessary to detect targetable mutations for the diagnosis, prognosis, and monitoring of cancer patients. Here, we employ standard genomic DNA (gDNA) and eight liquid biopsy samples from different cancer patients to examine the newly described CRISPR-Cas13a-based technology in the detection of the BRAF p.V600E actionable point mutation and appraise its diagnostic capacity with two PCR-based techniques: quantitative Real-Time PCR (qPCR) and droplet digital PCR (ddPCR). Regardless of its lower specificity compared to the qPCR and ddPCR techniques, the CRISPR-Cas13a-guided complex was able to detect inputs as low as 10 pM. Even though the PCR-based techniques have similar target limits of detection (LoDs), only the ddPCR achieved a 0.1% variant allele frequency (VAF) detection with elevated reproducibility, thus standing out as the most powerful and suitable tool for clinical diagnosis purposes. Our results also demonstrate how the CRISPR-Cas13a can detect low amounts of the target of interest, but its base-pair specificity failed in the detection of actionable point mutations at a low VAF; therefore, the ddPCR is still the most powerful and suitable technique for these purposes.

B-232 One Year Post-Implementation Experience Using a Custom Designed DNA Contamination Detection Module for a Clinical Myeloid Neoplasm Next Generation Sequencing Assay

Abstract Background In complex automated clinical laboratory Next Generation Sequencing (NGS) workflows, numerous opportunities exist for contamination events to occur. For oncology testing applications, detection of these events is crucial for accurate results reporting. A contamination detection module (MICon) using microhaplotype (MH) regions and an in-house designed analysis model was developed for use in a NGS assay for myeloid neoplasms (NGSHM) [1]. Variant detection for NGSHM has a validated analytical sensitivity of 2% variant allele frequency (VAF). Gross contamination events can potentially cause erroneous false positive variant detection whereas true low VAF mutations may be masked and evade detection. The following study was performed to evaluate MICon module performance on samples processed over the course of a year. Methods MH regions contain highly conserved tandem single nucleotide polymorphisms (SNPs) with high global heterogeneity occurring within a 300-nucleotide span. From the work of Kidd et al [2], 27 MH regions covering 92 SNPs and spanning 16 chromosomes were selected for inclusion in the 47 gene NGSHM target-capture panel. Sequencing was performed on a NovaSeq 6000 and analyzed through an internal bioinformatics pipeline, which incorporates the MICon module. MICon uses a binary classification model incorporating VAFs from MH regions, number of MH genotypes, and the contamination estimation score from verifyBamID to compute a single value on a 0-100 scale. Scores <50 are classified as non-contaminated and scores ≥50 require further investigation. Results The dataset was comprised of 10,990 samples. A total of 10,232 patient cases (93.1%) had non-contaminated MICon scores <50. Control replicates accounted for 261 samples (2.4%). There were 497 patient cases (4.5%) with MICon scores ≥50. Of the 497 patient cases, 137 (27.6%) had undergone hematopoietic stem cell transplantation (HSCT) and 114 (22.9%) contained gross chromosomal abnormalities, representing iatrogenic or tumor biological factors. An additional 135 (27.2%) of cases were contaminated from laboratory processing errors, 45 (9.1%) occurred due to chemistry failures during run processing, and 66 (13.2%) had an undetermined cause for a high score, representing laboratory-related and unknown factors. Overall, the 135 laboratory processing errors detected accounted for 1.3% of patient cases analyzed by the laboratory. These cases were repeated, and the non-contaminated results were accurately reported. Conclusions Herein it was shown the implementation of MICon has improved patient safety over the course of a year. The 1.3% of patient cases identified as arising from laboratory processing errors were successfully reprocessed. While the overall rate of laboratory processing errors appears low, the absolute number can be significant in a high-volume test setting, despite reliance on highly automated processes. Value is added by MICon through identifying errors that could result in the release of inaccurate patient results. By detecting previously unrealized errors, MICon has become an invaluable asset to the NGSHM assay by enhancing patient laboratory testing safety.

Comparing baseline VAF in circulating tumor DNA and tumor tissues predicting prognosis of patients with colorectal cancer liver metastases after curative resection

IntroductionThe prognostic value of baseline variant allele frequency (VAF) in circulating tumor DNA (ctDNA) of colorectal cancer liver metastases (CRLM) patients after curative resection was rarely investigated. MethodsA single-center prospective study was performed to investigate the prognostic impact of baseline VAF in ctDNA and matched tumor tissues of CRLM patients after curative resection between May 2019 and May 2021 by the Illumina NovoSeq 6000 platform. The relationship of the tumor burden score (TBS) and the VAF in ctDNA and matched tumor tissues was evaluated by the Pearson correlation method. The survival curves of recurrence-free survival (RFS) and overall survival (OS) were plotted. Factors associated with RFS were calculated using Cox regression analysis, and an integrated prognostic model using significant baseline variables was proposed. ResultsThere were 121 patients with baseline ctDNA and matched tumor tissues enrolled in the study. A total of 417 mutations spanning 20 genes were identified in baseline tumor tissues of 119/121 (98.3 %) cases. The overall mutations in tumor tissues were completely covered by ctDNA in 52 of 121(43.0 %) patients. Baseline VAF in ctDNA but not in tumor tissues was significantly correlated to TBS of CRLM (R = 0.36, p < 0.001). Significantly longer RFS but not OS was observed in patients with lower VAF in ctDNA compared to those with higher one (p < 0.001 and p = 0.33 respectively). Multivariate Cox regression analysis showed higher VAF in baseline ctDNA was an independent risk factor for RFS. An integrated prognostic model including baseline metastasis location and VAF in ctDNA outperformed the traditional CRS model in predicting RFS. ConclusionBaseline VAF in ctDNA but not in tumor tissues influenced RFS of CRLM patients after curative resection.

Molecular characteristics of NPM1 mutations in AML patients using targeted NGS

ABSTRACT Background Acute myeloid leukemia (AML) is a clonal hematopoietic stem cell malignancy characterized by the accumulation of myeloid progenitor cells with arrested differentiation, leading to the suppression of normal hematopoiesis. The disease exhibits significant heterogeneity, with less than 30% five-year overall survival. Nucleophosmin 1 (NPM1) is the most commonly mutated gene in adult AML, found in approximately 25–35% of patients, and is recognized as a distinct subtype by the WHO. Methods The mutational status of NPM1 was assessed using the Oncomine Myeloid research panel on the Ion5S NGS platform (Thermo Fisher Scientific, USA). Results In our AML cohort, NPM1 was the most frequently mutated gene (75%). Indel mutations in the NPM1 gene, frequently resulting in frameshift consequences, show a statistically significant difference in variant allele frequency (VAF) compared to other mutation types. Specifically, NPM1-mutated cases exhibit a VAF that is positively correlated with initial bone marrow (BM) blast counts. Univariate logistic regression analysis reveals that a high VAF is significantly associated with non-complete remission (Non-CR), while a low VAF is significantly associated with complete remission (CR), indicating a statistically significant difference in outcomes (p = 0.012). Conclusion Targeted NGS technology enables the simultaneous analysis of multiple AML-relevant genes, offering a comprehensive mutational profile that supports risk stratification, diagnosis, and personalized treatment. Our findings highlight the significant impact of NPM1 mutations on patient outcomes, revealing their molecular characteristics and their correlation with different clinical parameters.

Tislelizumab plus cetuximab and irinotecan in refractory microsatellite stable and RAS wild-type metastatic colorectal cancer: a single-arm phase 2 study

Immunotherapy confers little to no benefit in the treatment of microsatellite stable (MSS) metastatic colorectal cancer (mCRC). Mechanistic insights suggested that epidermal growth factor receptor (EGFR) antibody plus irinotecan might augment the tumor immune response in mCRC. Therefore, we conducted a proof-of-concept, single-arm, phase 2 study (ChiCTR identifier: ChiCTR2000035642) of a combination treatment regimen including tislelizumab (anti-PD-1), cetuximab (anti-EGFR) and irinotecan in 33 patients with MSS and RAS wild-type (WT) mCRC who were previously treated with ≥2 lines of therapy. The primary endpoint was met, with a confirmed objective response rate of 33%. As secondary endpoints, the disease control rate was 79%, and the median progression-free survival and overall survival were 7.3 and 17.4 months respectively. Among the 33 patients, 32 (97.0%) had treatment-related adverse events (AEs). Three (9.1%) reported grade ≥ 3 AEs, including rash (n = 1), neutropenia (n = 2). The post-hoc evaluation of dynamic circulating tumor DNA using next generation sequencing and the analysis of peripheral immune proteomics landscape using Olink revealed that lower variant allele frequency (VAF) at baseline, greater reduction in VAF on treatment, and a hot peripheral macroenvironment were associated with the treatment response independently. Our study showed the antitumor activity of tislelizumab, cetuximab, and irinotecan combination with a tolerable safety profile in previously treated MSS and RAS WT mCRC.

Diagnostic Yield of Trio Whole-Genome Sequencing in Children with Undiagnosed Developmental Delay or Congenital Anomaly: A Prospective Cohort Study.

Developmental delays (DD) and congenital anomalies (CA) are prevalent yet often remain undiagnosed despite comprehensive genetic testing. This study aims to investigate the diagnostic yield of trio whole-genome sequencing (WGS) in children presenting with DD or CA who remained undiagnosed after previous genetic testing. A prospective cohort study was conducted on children with undiagnosed DD or CA at a single tertiary hospital. All participants suspected of genetic conditions had undergone chromosome analysis, chromosome microarray analysis (CMA), and clinical exome sequencing (CES); however, a subset remained undiagnosed. The WGS test was administered to both the affected children and their parents. A total of 52 children were included, and 10 (19.2%) had undergone a genetic diagnosis through WGS. Eight of these cases were associated with autosomal dominant and de novo variants. WGS led to successful diagnosis due to several factors, including small structural variants, genes not covered in the CES panel, the discovery of newly implicated genes, issues related to coverage depth, low variant allele frequency, challenges in variant interpretation, and differences in the interpretation of variants of unknown significance among clinicians. This study highlights the clinical value of trio WGS testing in undiagnosed children with DD or CA. Notably, an additional 19.2% of affected children were diagnosed through this method.

An ultrasensitive DNA-enhanced amplification method for detecting cfDNA drug-resistant mutations in non-small cell lung cancer with selective FEN-assisted degradation of dominant somatic fragments.

Blood cell-free DNA (cfDNA) can be a new reliable tool for detecting epidermal growth factor receptor (EGFR) mutations in non-small cell lung cancer (NSCLC) patients. However, the currently reported cfDNA assays have a limited role in detecting drug-resistant mutations due to their deficiencies in sensitivity, stability, or mutation detection rate. We developed an Archaeoglobus fulgidus-derived flap endonuclease (Afu FEN)-based DNA-enhanced amplification system of mutated cfDNA by designing a pair of hairpin probes to anneal with wild-type cfDNA to form two 5'-flaps, allowing for the specific cleavage of wild-type cfDNA by Afu FEN. When the dominant wild-type somatic cfDNA fragments were cleaved by structure-recognition-specific Afu FEN, the proportion of mutated cfDNA in the reaction system was greatly enriched. As the amount of mutated cfDNA in the system was further increased by PCR amplification, the mutation status could be easily detected through first-generation sequencing. In a mixture of synthetic wild-type and T790M EGFR DNA fragments, our new assay still could detect T790M mutation at the fg level with remarkably high sensitivity. We also tested its performance in detecting low variant allele frequency (VAF) mutations in clinical samples from NSCLC patients. The plasma cfDNA samples with low VAF (0.1 and 0.5 %) could be easily detected by DNA-enhanced amplification. This system with enhanced amplification of mutated cfDNA is an effective tool used for the early screening and individualized targeted therapy of NSCLC by providing arapid, sensitive, and economical way for the detection of drug-resistant mutations in tumors.

Mutation-Selected Amplification droplet digital PCR: A new single nucleotide variant detection assay for [formula omitted] mutant in tumor and plasma samples

The early detection of gene mutations in physiological and pathological processes is a powerful approach to guide decisions in precision medicine. However, detecting low-copy mutant DNA from clinical samples poses a challenge due to the enrichment of wild-type DNA backgrounds. In this study, we devised a novel strategy, named Mutation-Selected Amplification droplet digital PCR (MSA-ddPCR), to quantitatively analyze single nucleotide variants (SNVs) at low variant allele frequencies (VAFs). Using TP53R249S (a hotspot mutation associated with hepatocellular carcinoma) as a model, we optimized the concentration ratio of primers, the annealing temperature and nucleic acid amplification modifiers. Subsequently, we evaluated the linear range and precision of MSA-ddPCR by detecting TP53R249S and TP53wild-type (TP53WT) plasmid DNA, respectively. MSA-ddPCR demonstrated superior ability to discriminate between mutant DNA and wild-type DNA compared to traditional TaqMan-MGB PCR. We further applied MSA-ddPCR to analyze the TP53R249S mutation in 20 plasma samples and 15 formalin-fixed paraffin-embedded (FFPE) tissue samples, and assessed the agreement rates between MSA-ddPCR and amplicon high-throughput sequencing. The results showed that the limit of blanks of MSA-ddPCR are 0.449 copies μL−1 in the FAM channel and 0.452 copies μL−1 in the VIC channel. MSA-ddPCR could accurately quantify VAFs as low as 0.01 %, surpassing existing PCR and next-generation sequencing (NGS) methods. In the detection of clinical samples, a high correlation was found between MSA-ddPCR and amplicon high-throughput sequencing. Additionally, MSA-ddPCR outperformed sequencing methods in terms of detection time and simplicity of data analysis. MSA-ddPCR can be easily implemented into clinical practice and serve as a robust tool for detecting mutant genes due to its high sensitivity and accuracy.

Unraveling morphology, methylation profiling, and diagnostic challenges in BRAF-Mutant pediatric glial and glioneuronal tumors.

To elucidate the relationship between DNA methylation profiling (DMP) and pathological diagnosis (PD) in pediatric glial and glioneuronal tumors with B-Raf proto-oncogene, serine/threonine kinase (BRAF) mutations, addressing their diagnostic challenges. This retrospective study, conducted in Saudi Arabia, analyzed 47 cases from the Children's Brain Tumor Network online database using scanned images, next-generation sequencing data, and methylation profiles processed using the Heidelberg methylation brain tumor classifiers v12.5 and v12.8. The data was last access on 10 November 2023. The highest prevalence of BRAF mutations was observed in pilocytic astrocytoma and ganglioglioma. The DMP was consistent with PD in 23 cases, but discrepancies emerged in others, including diagnostic changes in diffuse leptomeningeal glioneuronal tumor and polymorphous low-grade neuroepithelial tumor of the young. A key inconsistency appeared between a pilocytic astrocytoma MC and a glioneuronal tumor PD. Two high-grade astrocytomas were misclassified as pleomorphic xanthoastrocytomas. Additionally, low variant allelic frequency in gangliogliomas likely contributed to misclassifications as control in 5 cases. This study emphasized the importance of integrating DMP with PD in diagnosing pediatric glial and glioneuronal tumors with BRAF mutations. Although DMP offers significant diagnostic insights, its limitations, particularly in cases with low tumor content, necessitate cautious interpretation, as well as its use as a complementary diagnostic tool, rather than a definitive method.

Multi-regional sequencing reveals the genetic and immune heterogeneity of non-cancerous tissues in gastric cancer.

Gastric cancer (GC) is one of the most heterogeneous tumors. However, research on normal tissue adjacent to the tumor (NAT) is very limited. We performed multi-regional omics sequencing on 150 samples to assess the genetic basis and immune microenvironment in NAT and matched primary tumor or lymph node metastases. NATs demonstrated different mutated genes compared with GC, and NAT genomes underwent independent evolution with low variant allele frequency. Mutation profiles were predominated by aging and smoking-associated signatures in NAT instead of signatures associated with genetic instability. Although the immune microenvironment within NATs shows substantial intra-patient heterogeneity, the proportion of shared TCR clones among NATs is five times higher than that of tumor regions. These findings support the notion that subclonal expansion is not pronounced in NATs. We also demonstrated remarkable intra-patient heterogeneity of GCs and revealed heterogeneity of focal amplification of CD274 (encoding PD-L1) that leads to differential expression. Finally, we identified that monoclonal seeding is predominant in GC, which is followed by metastasis-to-metastasis dissemination in individual lymph nodes. These results provide novel insights into GC carcinogenesis. © 2024 The Pathological Society of Great Britain and Ireland.

Precision genome profiling for pediatric leukemia with a software-controlled enrichment method using nanopore sequencer.

10027 Background: The real-time nature of nanopore sequencing allows for simultaneous basecalling of DNA sequences during sequencing. This unique capability enables adaptive sampling (AS), a software-controlled targeted sequencing method. AS is notable for its ability to rapidly and flexibly enrich multiple genes with long fragment reads and detect various modalities of genetic aberrations in a single run. However, the feasibility and significance of AS for cancer have not been previously reported. Methods: We performed AS on a GridION sequencer using samples from 28 pediatric leukemia patients (10 acute myeloid leukemia, 13 B-cell acute lymphoblastic leukemia, and 5 T-cell acute lymphoblastic leukemia). Target regions were comprised of 466 genes associated with hematologic malignancies and included 30-kilo base pairs of flanking regions. After 3 days of sequencing, single-nucleotide variants (SNVs), structural variations (SVs), and copy number variations (CNVs) were determined. In 21 samples, variant calling accuracy was evaluated using short-read-based whole genome sequencing (WGS). Results: In the on-target regions, mean depth was 21.0× and N50 was 11,191 bps at the median. Of the 13 samples with genetic alterations previously detected through clinical testing for diagnostic classifications, all were reconfirmed by AS. Detecting DUX4 rearrangement needed an additional analysis pipeline because of its structural complexity. Among the 15 remaining samples whose genetic alterations had not been determined by clinical diagnostic testing, AS identified putative driver aberrations in 14 samples. All of these genomic abnormalities were structural variations (SVs) or copy number variations (CNVs), most of which were not encompassed within the genes or regions targeted in clinical diagnostic testing. Detected SVs were described with accurate genomic breakpoints, enabling the efficient detection of gene rearrangements and deletions of the entire region of an exon or a gene. Regarding CNVs, both chromosomal-level CNVs, such as high-hyperdiploid, and focal CNVs, such as CDKN2A deletion, were detectable using genome-wide low-coverage reads in the off-target regions. In the other case with acute myeloid leukemia in which genetic abnormalities were not detected either by clinical testing or AS, WGS identified an NPM1 frameshift deletion located outside of known hotspots. Among variants identified by WGS, AS detected 60.9% of the SNVs, 17.6% of the small indels, and 89.2% of the SVs, with a tendency of poor detection efficiency for variants with low variant allele frequency. Conclusions: AS provides a rapid and precise description of the genomic profile of pediatric leukemia, particularly advantageous for identifying SVs and CNVs, which are difficult to detect by capture-based short-read sequencing.

Therapeutic implications of acquired high tumor mutational burden (TMB-H) after targeted therapy (TT) in metastatic colorectal cancer (mCRC).

3542 Background: mCRC treated w/ TT can acquire a high number of mutations at progression. TMB is used as a proxy of neoantigen load for predicting benefit from immune checkpoint blockade (ICB). In TMB-H CRC, benefit to ICB is restricted to microsatellite unstable (MSI-H) hypermutated or POL-D/E ultramutated tumors. We asked whether TT can sensitize microsatellite stable (MSS) CRCs to ICB by inducing an acquired TMB-H state. Methods: We screened the MSK-IMPACT dataset for mCRC patients (pts) who received TT and underwent pre-treatment (pre-TT) and post-progression (post-TT) tissue or liquid biopsies (LBx). We included pts who received TT against EGFR, BRAF V600E, KRAS G12C, or HER2. DNA sequencing of tissue and LBx was performed w/ MSK-IMPACT and Guardant 360. MSI status was assessed with algorithms measuring somatic changes in length of repetitive sequences (e.g., MSIsensor). Due to known discrepancies between tissue TMB (tTMB) and blood TMB (bTMB), we defined acquired TMB-H as: 1) tTMB &lt;10 mut/Mb or bTMB &lt;20 mut/Mb pre-TT; 2) ≥5-fold increase in TMB post-TT; 3) tTMB ≥10 mut/Mb or bTMB ≥40 mut/Mb post-TT. Results: We identified 26 pts w/ paired samples that had been sequenced w/ determination of TMB. 4/26 (15%) met criteria for acquired TMB-H. None had detectable pathogenic mismatch repair or DNA damage repair alterations pre-TT. All 4 post-TT samples were LBx only. One pt’s tumor acquired a somatic MLH1 mutation and converted from MSS to MSI-H. In all cases, the majority of acquired mutations were subclonal w/ many at variant allele frequencies (VAF) of ≤1% (Table). After detection of acquired TMB-H, 2/4 pts received ICB. Pt 1 had RAS wild type mCRC w/ pre-TT tTMB 6.9. She received irinotecan + panitumumab for 25.8 months. Post-TT bTMB was 40.19 and met criteria for MSI-H. She received pembrolizumab and experienced clinical + radiographic progression of disease (POD) within 49 days. Pt 2 had KRASG12C-mutant mCRC w/ pre-TT bTMB 13.4 and tTMB 4.9. She received sotorasib + panitumumab for 3.2 months w/ post-TT bTMB 145.34. She received pembrolizumab + regorafenib and experienced clinical + radiographic POD within 37 days. Conclusions: In CRC, acquisition of TMB-H at progression w/ predominantly low VAF mutations suggests activation of enhanced mutagenesis due to therapeutic pressure from exposure to TT. In this context, TMB may not be an accurate reflection of tumor immunogenicity as it does not distinguish between clonal and subclonal alterations. Our data suggest that pts w/ acquired TMB-H following TT are unlikely to benefit from ICB. [Table: see text]

Modified Unit-Mediated Strand Displacement Reactions for Direct Detection of Single Nucleotide Variants in Active Double-Stranded DNA.

Accurate identification of single nucleotide variants (SNVs) in key driver genes holds a significant value for disease diagnosis and treatment. Fluorescent probes exhibit tremendous potential in specific, high-resolution, and rapid detection of SNVs. However, additional steps are required in most post-PCR assays to convert double-stranded DNA (dsDNA) products into single-stranded DNA (ssDNA), enabling them to possess hybridization activity to trigger subsequent reactions. This process not only prolongs the complexity of the experiment but also introduces the risk of losing target information. In this study, we proposed two strategies for enriching active double-stranded DNA, involving PCR based on obstructive groups and cleavable units. Building upon this, we explored the impact of modified units on the strand displacement reaction (SDR) and assessed their discriminatory efficacy for mutations. The results showed that detection of low variant allele frequencies (VAF) as low as 0.1% can be achieved. The proposed strategy allowed orthogonal identification of 45 clinical colorectal cancer tissue samples with 100% specificity, and the results were generally consistent with sequencing results. Compared to existing methods for enriching active targets, our approach offers a more diverse set of enrichment strategies, characterized by the advantage of being simple and fast and preserving original information to the maximum extent. The objective of this study is to offer an effective solution for the swift and facile acquisition of active double-stranded DNA. We anticipate that our work will facilitate the practical applications of SDR based on dsDNA.

Abstract PO4-13-07: Association of clonal hematopoiesis (CH) with clinical outcomes among survivors of breast cancer (BC)

Abstract Background: Clonal hematopoiesis (CH) refers to the identification of clonal expansion of hematopoietic cells due to somatic mutations in leukemia-associated genes without evidence of hematologic anomalies. CH, particularly with variant allele frequency (VAF) ≥ 10%, has been associated with adverse outcomes, including reduced survival in advanced malignancies and higher risk of cardiovascular events. The aim of this study was to evaluate the biological and prognostic relevance of CH in survivors of breast cancer (BC). Methods: CANTO (NCT01993498) is a prospective, multicenter cohort enrolling patients diagnosed with stage I-III BC. CANTO collects clinical, tumor and treatment-related characteristics at diagnosis (dx). Follow-up visits are scheduled at 1, 2, 4 and 6 years after dx and data on disease status, type of recurrence, and survival status are collected. We assessed CH among pts ≥ 40 years, without previous solid or hematological cancer, with blood samples available at dx and year 4 or experiencing death or disease recurrence before year 4. CH was determined using Next-Generation Sequencing with unique molecular identifiers (HaloPlexHS, Agilent Technologies) for 17 genes (including DNMT3A, TET2, ASXL1, PPM1D, ATM, JAK2 and TP53) on blood samples obtained at dx. Outcomes of interest included invasive disease-free survival (iDFS), distant disease-free survival (DDFS) and overall survival (OS) defined according to STEEP criteria. Kaplan-Meier estimator, log-rank test and multivariate Cox models assessed prognostic role of CH. Results: In the cohort with available CH data (N=1219) mean age (SD) was 57.5 (10.1) years, 62% of pts were postmenopausal, 40.9% were current or former smokers, 46.2% had stage I BC, 77.7% had HR+/HER2- BC, 53.5% received chemotherapy and 80.8% hormonal therapy. CH was detected with a VAF ≥ 1% in 306 pts (25.1%) including 207 pts (67.6%) with DNMT3A mutation, ≥ 2% in 186 (15.3%) and ≥ 10% in 45 (3.7%) pts. Pts with CH ≥ 10% were more frequently older (65.3 vs 57.2 years, p&amp;lt; .0001) and with a previous history of cardiovascular disease (53.3% vs 37.3%, p&amp;lt; 0.02). At a median (IQR) follow-up of 7.0 (6.2-7.8) years 246 iDFS, 161 DDFS and 118 OS events were observed. Only 8 cases of new hematological malignancies were observed. Pts harboring CH with a VAF ≥ 10% had worse OS (log-rank p=0.04) and CH with a VAF ≥ 10% was associated with higher risk of death (HR= 2.4, 95%CI 1.04-5.6); presence of CH with lower VAF was not associated with worse OS. Table displays complete results for all tested associations. Conclusions: CH at dx was identified in 25% of pts with stage I-III BC aged ≥ 40 years in the CANTO cohort, including 4% with a VAF ≥ 10%. In a large, prospective cohort of survivors of BC, we confirmed known associations of CH with older age and cardiovascular history. We observed few secondary hematological malignancies. CH with a VAF ≥ 10% was significantly associated with higher risk of death while adjusting for other relevant prognostic factors. Furthermore, a trend towards higher risk of DDFS events was observed among pts harboring CH with a VAF ≥ 10%. Table. Citation Format: Davide Soldato, Antonin Della Noce, Antonio Di Meglio, Christophe Marzac, Barbara Pistilli, Anne-Laure Martin, Sibille Everhard, Marie Breckler, Sandrine Boyault, Marina Rousseau, Olivier Trédan, Charles Coutant, Paul Cottu, Olivier Rigal, Christelle Levy, Christelle Jouannaud, Baptiste Sauterey, Nathalie Droin, Bastien Job, Aurélie Bertaut, Fabrice André, Ines Vaz Luis, Jean-Baptiste Micol. Association of clonal hematopoiesis (CH) with clinical outcomes among survivors of breast cancer (BC) [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-13-07.

Abstract PO3-14-11: Association between BRCA alterations detected by circulating tumor DNA and germline mutations in breast cancer patients: a retrospective mono-institutional analysis

Abstract Background: PARP inhibitors (PARPi) are a standard of care for breast cancer (BC) patients (pts) with germline BRCA (gBRCA) mutation, with benefit demonstrated also in patients with somatic (s) BRCA1/2 mutations. The use of circulating tumor (ct) DNA testing allows to detect resistant and actionable alterations in BC, but it could be associated with the incidental identification of germinal mutations. The aim of this study was to describe the incidence of both, somatic and germinal BRCA1/2 alterations, and the impact on the therapeutic outcomes in a retrospective BC cohort with clinical ctDNA testing for their BC. Materials and methods: A retrospective cohort of 245 BC pts that underwent ctDNA analysis (Guardant 360) between August 2014 and May 2023 at Weill Cornell Medical College was identified. Pts with at least a BRCA1/2 alteration, including variant of uncertain significant (VUS) and synonymous, were enrolled in the study. A descriptive analysis was performed. Results: Among 35 patients included, 34 had metastatic disease, the median age was 61 years old (IQR 40-67), and 65.7% were post-menopausal at diagnosis. 57.1% of pts had hormone receptor positive/HER2 negative (HR+/HER2-) BC, 20% had HER2 positive disease and 22.9% were triple-negative (TN) BC. Ten (28.6%) and 20 (57.1%) pts had a sBRCA1 or a sBRCA2 alteration on ctDNA, respectively; 5 pts (14.3%) had a coexisting sBRCA1/2 mutation. The median variant allele frequency (VAF) was 1.2% for BRCA1 and 2.7% for BRCA2 alterations. Furthermore, 53.3% and 6.7% of sBRCA1 and 40% and 8% of sBRCA2 mutations were identified as VUS and synonymous, respectively. The most common associated genomic alterations included TP53 (62.9%), ESR1 (20%) and PI3KCA (52%) with a median number of 4 variants (IQR 2-7). Next generation sequencing (NGS) testing on tissue was available for 3 patients: two demonstrated concordance with BRCA alterations detected by ctDNA, whereas no alteration in BRCA1/2 genes was found for the third patient despite the tissue analysis was performed at the same time of the ctDNA. Germline testing was available for 24 (69%) pts; a corresponding gBRCA1 mutation was found for 3 pts (VAF 48.6%-84.3%), and a gBRCA2 for 8 pts (VAF 26.7%-49.5%). Due to the small sample size, a univocal VAF cut-off to detect gBRCA1/2 mutations could not be calculated. Twenty-nine pts had a sBRCA1/2 mutation detected by ctDNA test before starting a new therapy; of these 55.2% had HR+/HER2- disease, while 17.2% and 27.6% were HER2 positive and TN BC, respectively. The median progression free survival (mPFS) was 10.3 (3.2-17.4) months (ms) and the 1-year and 2-year overall survival (OS) rates were 82.3% and 70.5%, respectively. The mPFS was 10.3 ms (0-25.0) for patients (n=16) that underwent chemotherapy, 5.6 ms (0-15.1) for those who had received endocrine therapy (n=9), and not reached for patients treated with PARPi (n=4). Conclusions: ctDNA analysis allows the detection of sBRCA1/2 mutations that could be missed by tissue-based testing. The identification of BRCA alterations on ctDNA could guide the use of germline testing even when these are present at a lower VAF than expected, with relevant impact on the therapeutic choices and family screening. Further evaluation to establish the impact of sBRCA1/2 detected by ctDNA on the therapeutic algorithm decision are needed. Citation Format: Letizia Pontolillo, Eleonora Nicolò, Laura Munoz Arcos, Carolina Reduzzi, Mara Serena Serafini, Amanda Kaylan Strickland, Nadia Bayou, Jeannine Donahue, Elisabetta Molteni, Lorenzo Gerratana, Diana Giannarelli, Eleni Andreopoulou, Emilio Bria, Massimo Cristofanilli. Association between BRCA alterations detected by circulating tumor DNA and germline mutations in breast cancer patients: a retrospective mono-institutional analysis [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-14-11.

Clinical management of TP53 mosaic variants found on germline genetic testing

BackgroundGermline heterozygous TP53 pathogenic variants (PVs) cause Li Fraumeni Syndrome (LFS, OMIM#151623). TP53 PVs at lower-than-expected variant allele frequencies (VAF) may reflect postzygotic mosaicism (PZM) or clonal hematopoiesis (CH); however, no guidelines exist for workup and clinical management. Patients and methodsRetrospective analysis of probands who presented to an academic cancer genetics program with a TP53 PV result on germline genetic testing. ResultsTwenty-one of 125 unrelated probands (17 %) were found to harbor a TP53 PV with VAF<30 % or a designation of “mosaic”. A diagnosis of PZM was made in nine (43 %) due to a clinical phenotype consistent with LFS with (n = 8) or without (n = 1) positive ancillary tissue testing. Twelve patients (57 %) were diagnosed with presumed CH (pCH) due to a diagnosis of a myeloproliferative neoplasm, negative ancillary tissue testing, clinical phenotype not meeting LFS criteria, no cancer, and/or no first cancer age<50. Of the 19 patients with biological offspring, nine had either partial or complete offspring testing, all negative. ConclusionsDetermining the etiology of low VAF TP53 PVs requires ancillary tissue testing and incorporation of clinical phenotype. Discerning PZM versus CH is important to provide optimal care and follow-up.