Search

Verification of detection power calculation. Comparison between the predicted detection power of 18 replicates and the actual fraction of those replicates that were called MRD+. 18 independent samples from a 1:100k dilution were probed with a 488 SNV panel (see methods). Replicates had their duplex consensus reads downsampled in increments of 10% and detection power was recalculated. Reported are the median and range of predicted detection powers for all replicates at each downsampling.

Early stage breast cancer cohort. (A) Overview of subtype distribution of cohort as well as the timing of blood draws relative to surgery and treatment. (B) REMARK diagram of the early stage breast cancer cohort. (C) Distribution of the number of mutations tracked for each patient.

Purpose:Existing cell-free DNA (cfDNA) methods lack the sensitivity needed for detecting minimal residual disease (MRD) following therapy. We developed a test for tracking hundreds of patient-specific mutations to detect MRD with a 1,000-fold lower error rate than conventional sequencing.Experimental Design:We compared the sensitivity of our approach to digital droplet PCR (ddPCR) in a dilution series, then retrospectively identified two cohorts of patients who had undergone prospective plasma sampling and clinical data collection: 16 patients with ER+/HER2− metastatic breast cancer (MBC) sampled within 6 months following metastatic diagnosis and 142 patients with stage 0 to III breast cancer who received curative-intent treatment with most sampled at surgery and 1 year postoperative. We performed whole-exome sequencing of tumors and designed individualized MRD tests, which we applied to serial cfDNA samples.Results:Our approach was 100-fold more sensitive than ddPCR when tracking 488 mutations, but most patients had fewer identifiable tumor mutations to track in cfDNA (median = 57; range = 2–346). Clinical sensitivity was 81% (n = 13/16) in newly diagnosed MBC, 23% (n = 7/30) at postoperative and 19% (n = 6/32) at 1 year in early-stage disease, and highest in patients with the most tumor mutations available to track. MRD detection at 1 year was strongly associated with distant recurrence [HR = 20.8; 95% confidence interval, 7.3–58.9]. Median lead time from first positive sample to recurrence was 18.9 months (range = 3.4–39.2 months).Conclusions:Tracking large numbers of individualized tumor mutations in cfDNA can improve MRD detection, but its sensitivity is driven by the number of tumor mutations available to track.

Overview schematic of MRD assay. MRD assay workflow from characterizing a primary tumor to determining if a blood draw contains evidence of residual disease.

Validation of tumor fraction confidence interval and effects of biological variability on tumor fraction inference. (A) Confidence intervals inferred from simulated data were aggregated into coverage probability for each condition and compared against theoretical coverage probability of 95% (see Methods). (B) Biological variability of clonal evolution loss was simulated by removing tumor evidence from a fraction of the fingerprint panel. Tumor fraction was calculated for simulated and original samples for comparison.

Patients who experienced local recurrence only after treatment for early stage breast cancer. cfDNA time points for all patients who experienced local recurrence only. End points represent time of last follow up or death.

Supplementary Methods

Supplementary Tables

Application of MRD testing to healthy donor cfDNA samples. Patient specific panels designed for 14 different patients were pooled together and applied to cfDNA collected from four different healthy donors. Reported are the number of sites where ctDNA was detected. We required at least two sites to call a sample MRD+.

Digital droplet PCR (ddPCR) testing for single mutation in dilution series. (A) The observed VAFs of HapMap serial dilutions measured by using a ddPCR assay for a single mutation (with three replicates) vs. the expected VAFs; (B) The representative ddPCR raw data and fluorescence intensity thresholds for determining positive or negative droplets.

Technical performance of the MRD Assay. All samples from early stage breast cancer cohort. Includes plasma cfDNA and buffy coat gDNA samples. Samples from the same patient and probed with the same panel are represented independently. (A) On target fraction calculated from Picard CollectHsMetrics and using pct_selected_bases. (B) Coefficient of variation of duplex fragment depth across fingerprint sites. (C) Fold 80 base penalty score for duplex fragment depth across fingerprint sites. (D, E) Error rate comparison between conventional sequencing (requiring Q20 base quality and removing duplicate fragments) and our duplex sequencing with added filters (see methods). (F) Fraction of total duplexes after downsampling raw reads. We considered a sample to be saturated if it still contained at least 95% of its duplexes after downsampling to 80% of its raw reads.

BACKGROUND Although interest in droplet-digital PCR technology (ddPCR) for cell-free circulating DNA (cfDNA) analysis is burgeoning, the technology is compromised by subsampling errors and the few clinical targets that can be analyzed from limited input DNA. The paucity of starting material acts as a “glass ceiling” in liquid biopsies because, irrespective how analytically sensitive ddPCR techniques are, detection limits cannot be improved past DNA input limitations. METHODS We applied denaturation-enhanced ddPCR (dddPCR) using fragmented genomic DNA (gDNA) with defined mutations. We then tested dddPCR on cfDNA from volunteers and patients with cancer for commonly-used mutations. gDNA and cfDNA were tested with and without end repair before denaturation and digital PCR. RESULTS By applying complete denaturation of double-stranded DNA before ddPCR droplet formation the number of positive droplets increased. dddPCR using gDNA resulted in a 1.9–2.0-fold increase in data-positive droplets, whereas dddPCR applied on highly-fragmented cfDNA resulted in a 1.6–1.7-fold increase. End repair of cfDNA before denaturation enabled cfDNA to display a 1.9–2.0-fold increase in data-positive signals, similar to gDNA. Doubling of data-positive droplets doubled the number of potential ddPCR assays that could be conducted from a given DNA input and improved ddPCR precision for cfDNA mutation detection. CONCLUSIONS dddPCR is a simple and useful modification in ddPCR that enables extraction of more information from low-input clinical samples with minor change in protocols. It should be applicable to all ddPCR platforms for mutation detection and, potentially, for gene copy-number analysis in cancer and prenatal screening.

Purpose:Existing cell-free DNA (cfDNA) methods lack the sensitivity needed for detecting minimal residual disease (MRD) following therapy. We developed a test for tracking hundreds of patient-specific mutations to detect MRD with a 1,000-fold lower error rate than conventional sequencing.Experimental Design:We compared the sensitivity of our approach to digital droplet PCR (ddPCR) in a dilution series, then retrospectively identified two cohorts of patients who had undergone prospective plasma sampling and clinical data collection: 16 patients with ER+/HER2− metastatic breast cancer (MBC) sampled within 6 months following metastatic diagnosis and 142 patients with stage 0 to III breast cancer who received curative-intent treatment with most sampled at surgery and 1 year postoperative. We performed whole-exome sequencing of tumors and designed individualized MRD tests, which we applied to serial cfDNA samples.Results:Our approach was 100-fold more sensitive than ddPCR when tracking 488 mutations, but most patients had fewer identifiable tumor mutations to track in cfDNA (median = 57; range = 2–346). Clinical sensitivity was 81% (n = 13/16) in newly diagnosed MBC, 23% (n = 7/30) at postoperative and 19% (n = 6/32) at 1 year in early-stage disease, and highest in patients with the most tumor mutations available to track. MRD detection at 1 year was strongly associated with distant recurrence [HR = 20.8; 95% confidence interval, 7.3–58.9]. Median lead time from first positive sample to recurrence was 18.9 months (range = 3.4–39.2 months).Conclusions:Tracking large numbers of individualized tumor mutations in cfDNA can improve MRD detection, but its sensitivity is driven by the number of tumor mutations available to track.

BACKGROUND The use of clinical samples and circulating cell-free DNA (cfDNA) collected from liquid biopsies for diagnostic and prognostic applications in cancer is burgeoning, and improved methods that reduce the influence of excess wild-type (WT) portion of the sample are desirable. Here we present enrichment of mutation-containing sequences using enzymatic degradation of WT DNA. Mutation enrichment is combined with high-resolution melting (HRM) performed in multiplexed closed-tube reactions as a rapid, cost-effective screening tool before targeted resequencing. METHODS We developed a homogeneous, closed-tube approach to use a double-stranded DNA-specific nuclease for degradation of WT DNA at multiple targets simultaneously. The No Denaturation Nuclease-assisted Minor Allele Enrichment with Probe Overlap (ND-NaME-PrO) uses WT oligonucleotides overlapping both strands on putative DNA targets. Under conditions of partial denaturation (DNA breathing), the oligonucleotide probes enhance double-stranded DNA-specific nuclease digestion at the selected targets, with high preference toward WT over mutant DNA. To validate ND-NaME-PrO, we used multiplexed HRM, digital PCR, and MiSeq targeted resequencing of mutated genomic DNA and cfDNA. RESULTS Serial dilution of KRAS mutation-containing DNA shows mutation enrichment by 10- to 120-fold and detection of allelic fractions down to 0.01%. Multiplexed ND-NaME-PrO combined with multiplexed PCR-HRM showed mutation scanning of 10–20 DNA amplicons simultaneously. ND-NaME-PrO applied on cfDNA from clinical samples enables mutation enrichment and HRM scanning over 10 DNA targets. cfDNA mutations were enriched up to approximately 100-fold (average approximately 25-fold) and identified via targeted resequencing. CONCLUSIONS Closed-tube homogeneous ND-NaME-PrO combined with multiplexed HRM is a convenient approach to efficiently enrich for mutations on multiple DNA targets and to enable prescreening before targeted resequencing.

Purpose Breast cancer is a heterogeneous disease. Immunohistochemistry has given rise to triple-negative carcinoma (TNC). Concomitantly, biological origins of neoplasia and its heterogeneity has been strongly debated in cancer stem cells (CSC) theme. This study investigates the prevalence of basal (BCC) and penta-negative carcinomas (5NC) in TNC and establishes associations with CSC (CD44CD24). Materials and methods 94 TNC were tested for CK5/6, HER1, CD44 and CD24, evaluated by a simple immunohistochemistry score and correlated with clinicopathological and survival data. Results BCC had higher tumor grades than 5NC ( p = 0.004). CD44 negativity ( p = 0.007) and CD44 − CD24 + phenotype ( p = 0.013) were associated with less vascular invasion amongst TNC. CD44 expression was associated with BCC ( p = 0.007). CD44 − CD24 −/low phenotype was associated with 5NC. None of the variables were associated with clinical outcome. Conclusion BCC and 5NC are closely related tumor subtypes. CD44 − CD24 −/low phenotype was associated with 5NC and CD44 − CD24 + phenotype was associated with vascular invasion. These results require histogenetic confirmation in larger studies.

Germline mutations in the TP53 gene are associated with Li-Fraumeni and Li-Fraumeni-Like Syndromes, characterized by increased predisposition to early-onset cancers. In Brazil, the prevalence of the TP53-p.R337H germline mutation is exceedingly high in the general population and in cancer-affected patients, probably as result of a founder effect. Several genotyping methods are used for the molecular diagnosis of LFS/LFL, however Sanger sequencing is still considered the gold standard. We compared performance, cost and turnaround time of Sanger sequencing, PCR-RFLP, TaqMan-PCR and HRM in the p.R337H genotyping. The performance was determined by analysis of 95 genomic DNA samples and results were 100% concordant for all methods. Sequencing was the most expensive method followed by TaqMan-PCR, PCR-RFLP and HRM. The overall cost of HRM increased with the prevalence of positive samples, since confirmatory sequencing must be performed when a sample shows an abnormal melting profile, but remained lower than all other methods when the mutation prevalence was less than 2.5%. Sequencing had the highest throughput and the longest turnaround time, while TaqMan-PCR showed the lowest turnaround and hands-on times. All methodologies studied are suitable for the detection of p.R337H and the choice will depend on the application and clinical scenario.

Presence of excess unaltered, wild-type DNA providing no information of biologic or clinical value may often mask rare alterations containing diagnostic or therapeutic clues for cancer. There is a growing demand for removing unaltered DNA over large pools-of-sequences, especially for applications in liquid biopsies with circulating DNA (cfDNA). We recently developed nuclease-assisted minor-allele enrichment with probe-overlap (NaME-PrO), a single-step approach that removes WT-DNA prior to DNA amplification, following which current genomic analysis processes remain unchanged. NaME-PrO employs a double-strand DNA-specific nuclease (DSN) and overlapping oligonucleotide-probes interrogating multiple DNA targets. Following genomic-DNA denaturation, the temperature is lowered and the probes form transient double-stranded regions with their targets, and DSN is added to provide nuclease digestion to the selected sites. Mutations create mismatches that inhibit DSN digestion; thus, subsequent amplification yields DNA with alterations enhanced at multiple targets. In this manner, WT DNA at hundreds or thousands of DNA regions can be digested simultaneously. We also show that addition of organic solvents like DMSO in the NaME-PrO reaction enables DNA denaturation at lower temperatures that do not inactivate the enzyme (DSN). This enables DSN addition from the beginning of the reaction, enabling homogeneous, closed-tube application of the approach and avoids contamination-prone sample manipulations due to open-tube addition of DSN enzyme after denaturation. Using NaME-PrO ± DMSO we demonstrate several-hundred-fold multiplexed mutation enrichment in diverse human samples on multiple clinically relevant targets in 50-plex reactions. Application with targeted resequencing of tumor-circulating DNA demonstrated detection of mutations at the 0.01-0.1% levels with few sequence reads. In ongoing studies aiming to detect minimal residual disease using cfDNA in late-stage breast cancer, we used tumor exome sequencing to identify multiple clonal mutations for individual patients. We then performed multiplexed NaME-PrO to trace the "tumor fingerprint" in plasma. In ~50-plex reactions we showed that the majority (>60%) of the tumor-specific mutations were also detected in plasma. To evaluate the ultimate sensitivity of the method to identify such "tumor fingerprints," we applied NaME-PrO in serial dilutions of cfDNA from breast cancer patients into cfDNA from cancer-free, normal patients. We demonstrated that dilutions down to 1,000-10,000-fold, corresponding to mutations at Citation Format: Fangyan Yu, Mariana Fitarelli-Kiehl, Ka Wai Leong, Viktor Adalsteinsson, Heather Parsons, Mike G. Makrigiorgos. Method for sensitive detection of tumor fingerprints in plasma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 941.

Detection of microsatellite-instability in colonoscopy-obtained polyps, as well as in plasma-circulating DNA, is frequently confounded by sensitivity issues due to co-existing excessive amounts of wild-type DNA. While also an issue for point mutations, this is particularly problematic for microsatellite changes, due to the high false-positive artifacts generated by polymerase slippage (stutter-bands). Here, we describe a nuclease-based approach, NaME-PrO, that uses overlapping oligonucleotides to eliminate unaltered micro-satellites at the genomic DNA level, prior to PCR. By appropriate design of the overlapping oligonucleotides, NaME-PrO eliminates WT alleles in long single-base homopolymers ranging from 10 to 27 nucleotides in length, while sparing targets containing variable-length indels at any position within the homopolymer. We evaluated 5 MSI targets individually or simultaneously, NR27, NR21, NR24, BAT25 and BAT26 using DNA from cell-lines, biopsies and circulating-DNA from colorectal cancer patients. NaME-PrO enriched altered microsatellites and detected alterations down to 0.01% allelic-frequency using high-resolution-melting, improving detection sensitivity by 500–1000-fold relative to current HRM approaches. Capillary-electrophoresis also demonstrated enhanced sensitivity and enrichment of indels 1–16 bases long. We anticipate application of this highly-multiplex-able method either with standard 5-plex reactions in conjunction with HRM/capillary electrophoresis or massively-parallel-sequencing-based detection of MSI on numerous targets for sensitive MSI-detection.

Germline TP53 mutations are associated with Li–Fraumeni syndrome, an autosomal dominant disorder characterized by a predisposition to multiple early-onset cancers including breast cancer (BC), the most prevalent tumor among women. The majority of germline TP53 mutations are clustered within the DNA-binding domain of the gene, disrupting the structure and function of the protein. A specific germline mutation in the tetramerization domain of p53, p.R337H, was reported at a high frequency in Southern and Southeastern Brazil. This mutation appears to result in a more subtle defect in the protein, which becomes functionally deficient only under particular conditions. Recent studies show that the BC phenotype in TP53 mutation carriers is often HER2 positive (63–83 %). Considering that the immunophenotype of BC among p.R337H carriers has not been reported, we reviewed immunohistochemistry data of 66 p.R337H carriers in comparison with 12 patients with other non-functional TP53 germline mutation. Although 75 % of carriers of these mutations showed significant HER2 overexpression (3+), corroborating previous studies, only 22.7 % of p.R337H patients had BC overexpressing HER2. These results reinforce the notion that different germline mutations in TP53 may predispose to BC via different mechanisms.

Aberrant methylation changes, often present in a minor allelic fraction in clinical samples such as plasma-circulating DNA (cfDNA), are potentially powerful prognostic and predictive biomarkers in human disease including cancer. We report on a novel, highly-multiplexed approach to facilitate analysis of clinically useful methylation changes in minor DNA populations. Methylation Specific Nuclease-assisted Minor-allele Enrichment (MS-NaME) employs a double-strand-specific DNA nuclease (DSN) to remove excess DNA with normal methylation patterns. The technique utilizes oligonucleotide-probes that direct DSN activity to multiple targets in bisulfite-treated DNA, simultaneously. Oligonucleotide probes targeting unmethylated sequences generate local double stranded regions resulting to digestion of unmethylated targets, and leaving methylated targets intact; and vice versa. Subsequent amplification of the targeted regions results in enrichment of the targeted methylated or unmethylated minority-epigenetic-alleles. We validate MS-NaME by demonstrating enrichment of RARb2, ATM, MGMT and GSTP1 promoters in multiplexed MS-NaME reactions (177-plex) using dilutions of methylated/unmethylated DNA and in DNA from clinical lung cancer samples and matched normal tissue. MS-NaME is a highly scalable single-step approach performed at the genomic DNA level in solution that combines with most downstream detection technologies including Sanger sequencing, methylation-sensitive-high-resolution melting (MS-HRM) and methylation-specific-Taqman-based-digital-PCR (digital Methylight) to boost detection of low-level aberrant methylation-changes.