A novel SERPINE1-FOSB fusion gene in pseudomyogenic hemangioendothelioma results in activation of intact FOSB and the PI3K-AKT-mTOR signaling pathway and responsiveness to sirolimus.

Pseudomyogenic hemangioendothelioma (PHE) is an extremely rare disease that affects mainly the young and more men than women. PHE are multicentric, locally aggressive, have low metastatic potential, and affect multiple tissue planes. Genetic aberrations are frequently detected in PHE and may play important roles in the occurrence, development, and treatment of this disease. In this study, we report a case of PHE with a novel SERPINE1-FOSB fusion gene. The fusion introduced a strong promoter near the coding region of FOSB, resulting in overexpression of intact FOSB. Immunohistochemical analysis showed overexpression of pAKT and mTOR in tumor cells, suggesting activation of the PI3K-AKT-mTOR signaling pathway. The patient responded well to targeted therapy with sirolimus, an mTOR inhibitor. Our study correlated dysregulation of a specific signaling pathway and the effectiveness of a targeted therapy to a specific genetic aberration. This information may be useful for future investigations of targeted therapeutics and provide a potential predictive biomarker for therapeutic effectiveness in PHE cases.

Penile pseudomyogenic hemangioendothelioma/epithelioid sarcoma-like hemangioendothelioma with a novel pattern of SERPINE1-FOSB fusion detected by RT-PCR--report of a case.

We experienced a rare case of penile mesenchymal tumor in a 43-year-old Japanese man. At least three nodules were observed around the penis. The tumors were composed of spindle- to oval-shaped atypical cells with and without prominent nucleoli. These cells were like myogenic cells, but negative for myogenic markers. They were positive for endothelial markers, such as ERG, Fli1 and CD31. They were also positive for nuclear and cytoplasmic FOSB which are not expressed in epithelioid hemangioendothelioma or epithelioid sarcoma. These pathological and immunohistochemical findings strongly suggested pseudomyogenic hemangioendothelioma/epithelioid sarcoma-like hemangioendothelioma (PHE/ES-HE). Since a recent report directly proved that two cases of PHE/ES-HE have SERPINE1-FOSB fusion gene by reverse transcription-polymerase chain reaction (RT-PCR), we examined whether the fusion gene is present or not in the present case by RT-PCR using fresh frozen surgical material. Sequencing of the PCR product revealed that this case has SERPINE1-FOSB fusion. The fusion pattern of our case was different from those of two previously reported cases. In our case, 86 nucleotides of SERPINE1 intron 1 were inserted between SERPINE1 exon 1 and the middle portion of FOSB exon 1, and a putative translation start codon was identified in SERPINE1 intron 1. Thus, this is the third case of PHE/ES-HE with SERPINE1-FOSB fusion proved by RT-PCR.