Potentially actionable kinase fusions in inflammatory myofibroblastic tumors.

Abstract

10513 Background: Inflammatory myofibroblastic tumor (IMT) is a rare mesenchymal neoplasm that harbors anaplastic lymphoma kinase (ALK) gene rearrangements in approximately 50% of cases. ALK inhibitors have been validated as an effective therapeutic approach in this subset of IMTs. The goal of this study was to characterize a series of IMTs using both immunohistochemistry (IHC) and next generation sequencing (NGS). Methods: 30 formalin-fixed, paraffin-embedded IMT specimens from 28 patients were evaluated by IHC for ALK expression using standard techniques. DNA was extracted and sequenced using a targeted capture-based NGS assay for 3769 exons of 236 cancer-related genes and 47 introns of 19 commonly rearranged genes, including 8 tyrosine kinases in a CLIA laboratory (Foundation Medicine). Selected specimens were also evaluated for ALK fusions by fluorescence in-situ hybridization (FISH). Results: 20 samples were ALK positive and 10 samples were ALK negative by IHC. Targeted NGS was successfully performed in 16/20 ALK positive and 10/10 ALK negative cases. Among the 16 ALK positive cases analyzed by NGS, 12 harbored ALK fusions with various 5’ gene fusion partners, including LMNA, TPM3, TPM4, SEC31A, TFG, RANBP2, and CLTC. The remaining 4 were also negative by FISH suggesting a different mechanism of ALK overexpression. Among the 10 ALK negative cases, 2 harbored ALK fusions (EML4-ALK, TPM3-ALK). In the other 8 ALK negative samples, 2 contained distinct ROS1 fusions (YWHAE-ROS1, TFG-ROS1) and 1 contained a PDGFRβ fusion (NAB2-PDGFRβ), none of which have been described in IMT samples to date. Overall, kinase gene fusions were identified in 18/26 (69%) evaluable samples. Conclusions: This study represents the most comprehensive NGS analysis of IMTs. 12/12(100%) ALK IHC and FISH positive cases contained ALK fusions, while 5/8 (63%) of distinct ALK IHC negative cases harbored kinase fusions, involving ALK, ROS1, or PDGFRβ. Since these fusions are all targetable with existing kinase inhibitors (i.e. crizotinib, dasatinib), this study suggests that IMTs should be routinely profiled for kinase fusions and not just by ALK IHC. Efforts are ongoing to identify “driver mutations” in the fusion-negative specimens.