Analytical performance evaluation of a commercial next generation sequencing liquid biopsy platform using plasma ctDNA, reference standards, and synthetic serial dilution samples derived from normal plasma.

BACKGROUND: Circulating tumor (ct) DNA assays performed in clinical laboratories provide tumor biomarker testing support for biopharmaceutical clinical trials. Yet it is neither practical nor economically feasible for many of these clinical laboratories to internally develop their own liquid biopsy assay. Commercially available ctDNA kits are a potential solution for laboratories seeking to incorporate liquid biopsy into their test menus. However, the scarcity of characterized patient samples and cost of purchasing validation reference standards creates a barrier to entry. In the current study, we evaluated the analytical performance of the AVENIO ctDNA liquid biopsy platform (Roche Sequencing Solutions) for use in our clinical laboratory. METHOD: Intra-laboratory performance evaluation of AVENIO ctDNA Targeted, Expanded, and Surveillance kits (Research Use Only) was performed according to College of American Pathologists (CAP) guidelines for the validation of targeted next generation sequencing assays using purchased reference standards, de-identified human plasma cell-free (cf) DNA samples, and contrived samples derived from commercially purchased normal and cancer human plasma. All samples were sequenced at read depths relevant to clinical settings using the NextSeq High Output kit (Illumina). RESULTS: At the clinically relevant read depth, Avenio ctDNA kits demonstrated 100% sensitivity in detecting single nucleotide variants (SNVs) at ≥0.5% allele frequency (AF) and 50% sensitivity in detecting SNVs at 0.1% AF using 20-40 ng sample input amount. The assay integrated seamlessly into our laboratory's NGS workflow with input DNA mass, target allele frequency (TAF), multiplexing, and number of reads optimized to support a high-throughput assay appropriate for biopharmaceutical trials. CONCLUSIONS: Our study demonstrates that AVENIO ctDNA liquid biopsy platform provides a viable alternative for efficient incorporation of liquid biopsy assays into the clinical laboratory for detecting somatic alterations as low as 0.5%. Accurate detection of variants lower than 0.5% could potentially be achieved by deeper sequencing when clinically indicated and economically feasible.

Multiparametric liquid biopsy analysis in metastatic prostate cancer.

Molecular profiling of prostate cancer with liquid biopsies, such as circulating tumor cells (CTCs) and cell-free nucleic acid analysis, yields informative yet distinct data sets. Additional insights may be gained by simultaneously interrogating multiple liquid biopsy components to construct a more comprehensive molecular disease profile. We conducted an initial proof-of-principle study aimed at piloting this multiparametric approach. Peripheral blood samples from men with metastatic castrate-resistant prostate cancer were analyzed simultaneously for CTC enumeration, single-cell copy number variations, CTC DNA and matched cell-free DNA mutations, and plasma cell-free RNA levels of androgen receptor (AR) and AR splice variant (ARV7). In addition, liquid biopsies were compared with matched tumor profiles when available, and a second liquid biopsy was drawn and analyzed at disease progression in a subset of patients. In this manner, multiparametric liquid biopsy profiles were successfully generated for each patient and time point, demonstrating the feasibility of this approach and highlighting shared as well as unique cancer-relevant alterations. With further refinement and validation in large cohorts, multiparametric liquid biopsies can optimally integrate disparate but clinically informative data sets and maximize their utility for molecularly directed, real-time patient management.

Reference Size Matching, Whole-Genome Amplification, and Fluorescent Labeling as a Method for Chromosomal Microarray Analysis of Clinically Actionable Copy Number Alterations in Formalin-Fixed, Paraffin-Embedded Tumor Tissue.

Cancer genome copy number alterations (CNAs) assist clinicians in selecting targeted therapeutics. Solid tumor CNAs are most commonly evaluated in formalin-fixed, paraffin-embedded (FFPE) tissue by fluorescence in situ hybridization. Although fluorescence in situ hybridization is a sensitive and specific assay for interrogating preselected genomic regions, it provides no information about coexisting clinically significant copy number changes. Chromosomal microarray analysis is an alternative DNA-based method for interrogating genome-wide CNAs in solid tumors. However, DNA extracted from FFPE tumor tissue produces an essential, yet problematic, sample type. The College of American Pathologists/American Society of Clinical Oncology guidelines for optimal tumor tissue handling, published in 2007 for breast cancer and in 2016 for gastroesophageal adenocarcinomas, are lacking for other solid tumors. Thus, cold ischemia times are seldom monitored in non-breast cancer and non-gastroesophageal adenocarcinomas, and all tumor biospecimens are affected by chemical fixation. Although intended to preserve specimens for long-term storage, formalin fixation causes loss of genetic information through DNA damage. Herein, we describe a reference size matching, whole-genome amplification, and fluorescent labeling method for FFPE-derived DNA designed to improve chromosomal microarray results from suboptimal nucleic acids and salvage highly degraded samples. With this technological advance, whole-genome copy number analysis of tumor DNA can be reliably performed in the clinical laboratory for a wide variety of tissue conditions and tumor types.

Genomic Rearrangements of PTEN in Prostate Cancer.

The phosphatase and tensin homolog gene (PTEN) on chromosome 10q23.3 is a negative regulator of the PIK3/Akt survival pathway and is the most frequently deleted tumor suppressor gene in prostate cancer. Monoallelic loss of PTEN is present in up to 60% of localized prostate cancers and complete loss of PTEN in prostate cancer is linked to metastasis and androgen-independent progression. Studies on the genomic status of PTEN in prostate cancer initially used a two-color fluorescence in situ hybridization (FISH) assay for PTEN copy number detection in formalin fixed paraffin embedded tissue preparations. More recently, a four-color FISH assay containing two additional control probes flanking the PTEN locus with a lower false-positive rate was reported. Combined with the detection of other critical genomic biomarkers for prostate cancer such as ERG, androgen receptor, and MYC, the evaluation of PTEN genomic status has proven to be invaluable for patient stratification and management. Although less frequent than allelic deletions, point mutations in the gene and epigenetic silencing are also known to contribute to loss of PTEN function, and ultimately to prostate cancer initiation. Overall, it is clear that PTEN is a powerful biomarker for prostate cancer. Used as a companion diagnostic for emerging therapeutic drugs, FISH analysis of PTEN is promisingly moving human prostate cancer closer to more effective cancer management and therapies.

Challenges in the codevelopment of companion diagnostics.

Therapeutics harnessing the power of personalized medicine have the potential to revolutionize healthcare. Companion diagnostics are critical to this goal and are increasingly relied upon to ensure the effective, safe development and use of a personalized therapeutic. Companion diagnostics are the focus of several recent regulatory guidance documents; the drug-diagnostic codevelopment process has become increasingly relevant and necessary. Despite this, the promise of companion diagnostics has not been fully realized and there are multiple difficulties that still need resolution. The path to codevelop a successful companion diagnostic with its complementary drug is complex, fragmented and fraught with several challenges. In this article, we discuss the logistic, strategic business, regulatory and financial challenges involved in drug-companion diagnostic codevelopment.

FISH as an effective diagnostic tool for the management of challenging melanocytic lesions.

BACKGROUND: The accuracy of melanoma diagnosis continues to challenge the pathology community, even today with sophisticated histopathologic techniques. Melanocytic lesions exhibit significant morphological heterogeneity. While the majority of biopsies can be classified as benign (nevus) or malignant (melanoma) using well-established histopathologic criteria, there exists a cohort for which the prediction of clinical behaviour and invasive or metastatic potential is difficult if not impossible to ascertain on the basis of morphological features alone. Multiple studies have shown that there is significant disagreement between pathologists and even expert dermatopathologists in the diagnosis of this subgroup of difficult melanocytic lesions. METHODS: A four probe FISH assay was utilized to analyse a cohort of 500 samples including 157 nevus, 176 dysplastic nevus and 167 melanoma specimens. RESULTS: Review of the lesions determined the assay identified genetic abnormalities in a total of 83.8% of melanomas, and 1.9% of nevus without atypia, while genetic abnormalities were identified in 6.3%, 6.7%, and 10.3% of nevus identified with mild, moderate and severe atypia, respectively. CONCLUSIONS: Based on this study, inheritable genetic damage/instability identified by FISH testing is a hallmark of a progressive malignant process, and a valuable diagnostic tool for the identification of high risk lesions.

Acquired inv(9): what is its significance?

Pericentric inversion of the heterochromatic region of chromosome 9 [inv(9)] is a common heteromorphism in the general population. It is presumed familial as there are no reports of de novo inv(9) chromosomes in constitutional karyotypes. We report 2 cases of acquired inv(9) chromosomes; 1 patient with acute myeloid leukemia, 46,XY,inv(9)(p11q13)[11]/46,XY[9], and a second with severe anemia, 46,XX,inv(9)(p11q13)[14]/46,XX[6]. The acquired nature of the inv(9) was confirmed by constitutional karyotyping and/or molecular analysis. The inv(9) in these patients may be a de novo inversion that cytogenetically mimics the constitutional inv(9) heteromorphism. Alternatively, it may be the result of neocentromere activation in 9q due to epigenetic events associated with the disease in these patients that results in a metacentric chromosome similarly mimicking the constitutional inv(9). One previous report of an acquired inv(9) was in a patient with essential thrombocythemia. The differences in clinical presentation may represent different underlying mechanisms generating the inv(9). The significance of an acquired inv(9) is unknown and will require reporting of additional cases.

A multiplex methylation PCR assay for identification of uniparental disomy of chromosome 7.

Uniparental disomy of chromosome 7 (UPD7) is associated with abnormal phenotypic effects because of inappropriate expression of imprinted genes on chromosome 7. Based on the differential methylation of the promoter region of the imprinted PEG1/MEST locus at 7q32, we designed a multiplex methylation PCR (mPCR) assay to rapidly distinguish UPD7 from biparental inheritance of chromosome 7. Primers were designed to produce different sized PCR amplicons based on the parent of origin-specific methylation at this locus; electrophoresis of PCR amplicons showed a 189-bp product from the methylated maternal allele and a 109-bp product from the unmethylated paternal allele. This mPCR assay correctly predicted the chromosome 7 imprinting status in normal control and UPD7 samples. Previous assays for UPD7 required genotyping of the proband and parents, or separate maternal- and paternal-specific mPCR reactions. The advantage of this assay is that parental samples are not required and that amplification of both alleles in the same reaction is simpler and provides an internal control. This multiplex mPCR assay will be useful in screening for UPD7 in patients with Silver-Russell syndrome (SRS; also Russell-Sliver syndrome, RSS), primordial growth retardation, and in patients with supernumerary marker chromosomes or chromosome rearrangements of chromosome 7 origin.