(P 049) IMPLEMENTATION OF A ROUTINE DIAGNOSTIC NEXT GENERATION SEQUENCING PANEL OF FUSION-POSITIVE SARCOMAS: A SINGLE CENTER EXPERIENCE

Objective: Sarcomas represent a heterogeneous group of cancers with over 70 different subtypes identified to date. Up to a third of cases carry specific gene fusions that can be utilized for diagnostic purposes. Conventional reverse-transcriptase polymerase chain reaction (RT-PCR) and cytogenetic techniques are routinely used to identify those fusions. However, in recent years, next generation sequencing technologies (NGS) have demonstrated their superiority over conventional techniques in identifying a growing number of gene fusions thereby improving the diagnostic accuracy and classification of sarcomas. The aim of this study is to demonstrate the clinical utility of a routine diagnostic NGS fusion panel in a tertiary sarcoma center.

Methods: From December 2020 to February 2022, newly diagnosed unclassifiable sarcomas or cases suspected of possibly carrying a fusion based on histology have undergone routine NGS testing. Biopsy specimens including nonfrozen, formalin-fixed specimens or fresh frozen tissue were submitted for analysis. Samples were sequenced with the TruSight RNA Pan-Cancer panel that covers over 1385 fusion-associated genes. Only fusions read with high confidence were reported.

Results: We retrospectively studied 171 samples submitted for routine NGS testing at our institution. 30 (17.5%) samples failed the quality control to undergo NGS testing because of insufficient RNA extraction (56.7%) or insufficient number of reads (43.3%). Diagnostic fusions were found in 71 (41.5%) distinct specimens. Among the documented fusions by NGS, 39 (54.9%) cases would not have been identified with conventional molecular techniques. The initial sarcoma diagnosis was modified in 35 (49.3%) fusion-positive cases following the gene fusion discovery. Among the gene fusion-positive cases, actionable gene fusions were found in 5 (7.0%) cases and included one ALK- gene rearrangement in an inflammatory myofibroblastic tumor, 2 PDGFR-gene rearrangements in dermatofibrosarcoma protuberans sarcomas and 2 NTRK-rearrangements in unclassifiable sarcomas. Among the documented gene fusions, 9 were not previously described (Table 1).

Conclusion: Our study supports the role of NGS technologies in improving diagnostic accuracy and classification of sarcomas. Few fusions were actionable by drug therapy. As diagnostic RNA-fusion panels become routinely used in sarcoma referral centers, an increasing number of novel fusions are expected to be documented furthermore supporting the critical role of NGS in routine practice.

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