| Sumario: | Context.--Sarcomas are rare and highly heterogeneous mesenchymal tumors with deceptive morphologic features that pose a challenge for precise diagnostics. Chromosomal rearrangements generating pathognomonic gene fusions are useful diagnostic markers, traditionally tested using single-plex standard of care assays with limited diagnostic yield. NanoString nCounter technology has emerged as a robust solution with multiplexing capabilities. Objective.--To optimize NanoString effective coverage of specific entities and conduct a validation study to support its clinical implementation. Design.--We reconfigured a NanoString codeset by including a set of probes for detecting gene fusion variants of solitary fibrous tumors, low-grade fibromyxoid sarcomas/sclerosing epithelioid fibrosarcomas, and undifferentiated small round cell sarcomas, totaling 188 probes. A technical validation study was conducted with 96 retrospective samples. Additionally, 76 prospective samples were evaluated to assess the assay's clinical performance. Results.--Both technical and clinical validation studies showed that NanoString's codeset reached >88% sensitivity and 100% specificity, compared with standard of care methods, and superior diagnostic yield as a first-line test. Our design enabled the detection of almost all fusion variants of NGFI-A binding protein 2 (NAB2) with signal transducer and activator of transcription 6 (STAT6) in solitary fibrous tumors, as well as cAMP responsive element binding protein 3 like 1/2 (CREB3L1/2) rearrangements in all low-grade fibromyxoid sarcoma/sclerosing epithelioid fibrosarcoma cases. Identification of specific gene fusions of undifferentiated small round cell sarcoma was also improved, but additional strategies are necessary to attain full coverage. Conclusions.--The NanoString platform demonstrated good sensitivity, specificity, and superior diagnostic yield. It is a cost-effective assay with rapid turnaround time, low sample consumption, streamlined analysis, and easy customization. Therefore, it is a promising alternative first-line diagnostic tool for routine sarcoma testing.
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