Rhabdomyosarcomas with TFCP2 fusions represent an emerging subtype of tumors, initially discovered by RNA-sequencing. We report herein the clinicopathological, transcriptional and genomic features of a series of 14 cases.Cases were retrospectively and prospectively recruited and studied by immunohistochemistry (MYF4, MYOD1, S100, AE1/E3, ALK), fluorescence in situ hybridization with TFCP2 break-apart probe (n=10/14), array-comparative genomic hybridization (Agilent), whole RNA-sequencing (Truseq Exome, Illumina) or anchored multiplex PCR based targeted next-generation sequencing (Archer® FusionPlex® Sarcoma kit). Patient's age ranged between 11 to 86 years, including 5 pediatric cases. Tumors were located in bone (n=12/14) and soft tissue (n=2/14). Most bone tumors invaded surrounding soft tissue. Craniofacial bones were over-represented (n=8/12). Median survival was 8 months and 5 patients are currently alive with a median follow-up of 20 months. Most tumors displayed a mixed spindle cell and epithelioid pattern with frequent vesicular nuclei. All tumors expressed keratins and showed a rhabdomyogenic phenotype (defined as expression of MYF4 and/or MYOD1). ALK was overexpressed in all but 3 cases without underlying ALK fusion on break-apart FISH (n=5) nor next generation sequencing (n=14).TFCP2 was fused in 5' either to EWSR1 (n=6) or FUS (n=8). EWSR1 was involved in both soft tissue cases. FISH with TFCP2 break-apart probe was positive in all tested cases (n=8), including one case with unbalanced signal. On array-CGH, all tested tumors displayed complex genetic profiles with genomic indexes ranging from 12.8 to 90 and CDKN2A deletion was recurrent (n=9/10). FET-TFCP2 rhabdomyosarcomas clustered together and distinctly from other rhabdomyosarcomas subgroups.Altogether, our data confirm and expand the spectrum of the new family of FET-TFCP2 rhabdomyosarcomas which are associated with a predilection for the craniofacial bones, an aggressive course and recurrent pathological features. Their association with ALK overexpression might represent a therapeutic vulnerability.

Background Malignant peripheral nerve sheath tumor (MPNST) constitutes the leading cause of neurofibromatosis type 1–related mortality. MPNSTs contain highly rearranged hyperploid genomes and exhibit a high division rate and aggressiveness. We have studied in vitro whether the mitotic kinesins KIF11, KIF15, and KIF23 have a functional role in maintaining MPNST cell survival and can represent potential therapeutic vulnerabilities. Methods We studied the expression of kinesin mRNAs and proteins in tumors and cell lines and used several in vitro functional assays to analyze the impact of kinesin genetic suppression (KIF15, KIF23) and drug inhibition (KIF11) in MPNST cells. We also performed in vitro combined treatments targeting KIF11 together with other described MPNST targets. Results The studied kinesins were overexpressed in MPNST samples. KIF15 and KIF23 were required for the survival of MPNST cell lines, which were also more sensitive than benign control fibroblasts to the KIF11 inhibitors ispinesib and ARRY-520. Co-targeting KIF11 and BRD4 with ARRY-520 and JQ1 reduced MPNST cell viability, synergistically killing a much higher proportion of MPNST cells than control fibroblasts. In addition, genetic suppression of KIF15 conferred an increased sensitivity to KIF11 inhibitors alone or in combination with JQ1. Conclusions The mitotic spindle kinesins KIF11 and KIF15 and the cytokinetic kinesin KIF23 play a clear role in maintaining MPNST cell survival and may represent potential therapeutic vulnerabilities. Although further in vivo evidences are still mandatory, we propose a simultaneous suppression of KIF11, KIF15, and BRD4 as a potential therapy for MPNSTs.

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