A novelCLTC-FOSBgene fusion in pseudomyogenic hemangioendothelioma of bone

Pseudomyogenic hemangioendothelioma, an uncommon mesenchymal neoplasm composed of plump spindled and/or epithelioid endothelial cells, may present multicentrically and tends to locally recur but rarely metastasizes. Morphologic resemblance to epithelioid sarcoma and other spindle cell neoplasms may result in diagnostic confusion. Molecular characterization of pseudomyogenic hemangioendothelioma has revealed these neoplasms often harbor a rearrangement of theFOSBgene withSERPINE1orACTBas recurrent fusion gene partners. Herein, a case of a fibular pseudomyogenic hemangioendothelioma with minimal extension into the adjacent soft tissue arising in a 17 year-old male is presented. The neoplasm exhibited sheets of epithelioid cells with abundant eosinophilic cytoplasm and variably eccentric nuclei. RNA sequencing revealed a novelCLTC-FOSBfusion transcript that was subsequently confirmed by direct sequencing of reverse transcription-polymerase chain reaction products demonstrating an in-frame fusion between exon 17 of the clathrin heavy chain (CLTC) gene and exon 2 of theFOSB(FosB proto-oncogene, AP-1 transcription factor subunit) gene.CLTC-FOSBfusion has not been described in a neoplasm before.

Automated summary

Pseudomyogenic hemangioendothelioma is a rare mesenchymal tumor that often presents multicentric growth and tends to locally recur. Molecular characterization revealed frequent FOSB gene rearrangements with fusion gene partners like SERPINE1 or ACTB. A novel CLTC-FOSB fusion transcript was discovered in this case, demonstrating an in-frame fusion between exon 17 of the CLTC gene and exon 2 of the FOSB gene.