Pulmonary lipomatous hemangiopericytoma: report of a rare tumor and comparison with solitary fibrous tumor

Lipomatous Solitary Fibrous Tumors Harbor Rare NAB2-STAT6 Fusion Variants and Show Up-Regulation of the Gene PPARG, Encoding for a Regulator of Adipocyte Differentiation

Solitary fibrous tumors (SFTs) harbor activating NAB2-STAT6 gene fusions. Different variants of the NAB2-STAT6 gene fusion have been associated with distinct clinicopathologic features. Lipomatous SFTs are a morphologic variant of SFTs, characterized by a fat-forming tumor component. Our aim was to evaluate NAB2-STAT6 fusion variants and to further study the molecular genetic features in a cohort of lipomatous SFTs. A hybrid-capture-based next-generation sequencing panel was employed to detect NAB2-STAT6 gene fusions at the RNA level. In addition, the RNA expression levels of 507 genes were evaluated using this panel, and were compared with a control cohort of nonlipomatous SFTs. Notably, 5 of 11 (45%) of lipomatous SFTs in the current series harbored the uncommon NAB2 exon 4-STAT6 exon 4 gene fusion variant, which is observed in only 0.9% to 1.4% of nonlipomatous SFTs. Furthermore, lipomatous SFTs displayed significant differences in gene expression compared with their nonlipomatous counterparts, including up-regulation of the gene peroxisome proliferator activated receptor-γ (PPARG). Peroxisome proliferator activated receptor-γ is a nuclear receptor regulating adipocyte differentiation, providing a possible explanation for the fat-forming component in lipomatous SFTs. In summary, the current study provides a possible molecular genetic basis for the distinct morphologic features of lipomatous SFTs.

Pleural fat-forming variant of solitary fibrous tumor

The fat-forming variant of solitary fibrous tumor is rare. It occurs predominantly in the deep soft tissues of the retroperitoneum and thigh. We describe a case of fat-forming solitary fibrous tumor arising from the pleura, which was successfully treated using a video-assisted thoracoscopic approach. The patient remained free of recurrence 2 years after surgery and continues to be under long-term follow-up.

Fat-forming variant of solitary fibrous tumour of the pleura: CT findings

The fat-forming variant of solitary fibrous tumour (SFT) was previously called lipomatous haemangiopericytoma and is a rare variant of solitary fibrous tumour. It predominantly occurs in the deep soft tissues of the retroperitoneum and thigh. Only a handful of cases involving the perineum, spine, thoracic wall and pelvic cavity have been reported in the radiological literature and the fat-forming variant of SFT involving the pleura has not been previously reported. Herein, we report the CT findings of a case of the fat-forming variant of SFT involving the pleura that was treated by excision. Chest CT showed a large lobulated heterogeneous fatty mass with a multifocal enhancing soft-tissue component in the left lower hemithorax. Although rare, the fat-forming variant of SFT of the pleura should be added to the differential diagnosis of fat-containing pleural soft-tissue tumours.

Lipomatous hemangiopericytoma of the stomach: A case report and a review of literature

Lipomatous hemangiopericytomas (LHPCs) are rare soft-tissue tumors that are histologically characterized by hemangiopericytomatous vasculature and the presence of mature adipocytes. We present the clinicopathological features of a case of gastric LHPC in a 56-year-old female, along with a literature review. Endoscopy and endoscopic ultrasound showed a submucosal tumor 0.8 cm across in the greatest dimension in the lesser curvature side of the gastric antrum. Grossly, the well-defined mass had a solid and tan-white cut surface admixed with myxoid regions and yellowish areas. Histological examination revealed a submucosal well-circumscribed lesion composed of cellular nodules with the classic appearance of an hemangiopericytoma admixed with clusters and lobules of mature adipocytes. The ill-defined tumor cells had weakly eosinophilic cytoplasm and contained spindled nuclei with occasional small nucleoli. Nuclei atypia and mitoses were absent, and no cellular atypia, necrosis or vascular invasion was observed. Immunohistochemistry showed that the tumor cells were diffusely positive for CD34, CD99, and vimentin and were focally reactive for bcl-2. This is the first known report of an LHPC in the stomach. The patient was followed for 12 mo without any evidence of metastasis or recurrence.

Fat-forming solitary fibrous tumour (lipomatous haemangiopericytoma) of the spine: case report and literature review

Solitary fibrous tumour (SFT) is a rare soft tissue tumour of uncertain histogenesis and unpredictable biological behaviour, which was first described in the pleura and subsequently in many extra-pleural locations. Fat-forming SFT is a sub-type of SFT and only a handful of cases have been reported in the literature. We present the clinical, radiological and histological features of a case of intraspinal fat-forming SFT, along with a literature review. This is the first known report of a fat-forming SFT in the spine.