Journal Club

Novel molecular assay: Promising results in bone and soft tissue tumor evaluation



A novel method for detection of translocations appears to be superior to conventional molecular assays in the evaluation of bone and soft tissue tumor samples, according to researchers.

The technique of anchored multiplex polymerase chain reaction (AMP)–based targeted next-generation sequencing (NGS) had a failure rate of 14% but, nonetheless, worked favorably when compared with conventional techniques, which were associated with several false positives in this study, the researchers reported in the Journal of Molecular Diagnostics.

Two new fusion partners for the USP6 gene were found using AMP-based targeted NGS in this study, which thus contributed to the “further unraveling of the molecular landscape” for these tumors, added corresponding author Judith V.M.G. Bovée, MD, PhD, of the department of pathology at Leiden (the Netherlands) University Medical Center and her colleagues.

While the genetics of bone and soft tissue tumors have diagnostic value in clinical practice, standard fluorescence in situ hybridization (FISH) and reverse transcriptase PCR are associated with several drawbacks, such as a high false negative rate in the case of FISH, Dr. Bovée and her coauthors wrote.

Accordingly, the researchers evaluated the applicability of a targeted sequencing assay (Archer FusionPlex Sarcoma kit, which was developed by ArcherDX) aimed at 26 genes relevant to bone and soft tissue tumor diagnostics.

Besides allowing for assessment of multiple target genes in a single assay, this technique circumvents the need to know both fusion partners for translocation detection, which opens up the possibility of identifying novel or rare fusion partners, investigators noted.

AMP-based targeted NGS was used to evaluate 81 bone and soft tissue tumor samples, and of those, 48 cases showed a fusion. For the remaining 33 cases in which no fusion was detected, 22 were considered truly negative because samples met all criteria for good quality, while the remaining 11 (14%) were considered not reliable because of insufficient quality, investigators reported.

The samples were also evaluated through use of FISH, reverse transcriptase PCR, or both in 58 cases and use of immunohistochemistry in 16 cases; for the remaining seven cases, no assay or immunohistochemistry could be applied because of a lack of availability, according to investigators.

Among the 48 entities that were fusion-positive according to AMP-based targeted NGS, 29 were validated using standard molecular assays, and of those, 25 had concordant results. Further analysis of the four discordant cases with a third independent technique confirmed the AMP-based targeted NGS findings, according to the published report.

Among the 22 fusion-negative high-quality samples, 19 were validated using FISH, and one case was found to be discordant; however, despite use of a third independent technique, this discrepancy could not be resolved, investigators said.

The AMP-based targeted NGS technique identified COL1A1 and SEC31A as novel fusion partners for USP6 in two cases of nodular fasciitis. Those fusion partners had been previously described in aneurysmal bone cysts, according to investigators.

Despite the promising results for the novel assay, conventional methods were sufficient in this study to confirm translocations in straightforward cases and ordinary rearrangements, according to the investigators.

“Both reverse transcription PCR and FISH are not only quick and easy to conduct but are also of low cost and high analytical validity and accuracy, which make them attractive methods,” they wrote.

The work by Dr. Bovée and her colleagues was supported by Leiden University Medical Center. The department of pathology and the department of cell and chemical biology at the medical center receive royalty payments from Kreatech/Leica, which provided a COL1A1/PDGFB fusion probe used in the research.

SOURCE: Lam SW et al. J Mol Diagn. 2018 Aug 20;20(5):653-63.

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