Malignant giant solitary fibrous tumour of the mediastinum; masquerading Triton tumour

Arshi Beg,Jeenal Parikh ,Amit Janu,Rajiv Kumar Kaushal

doi:10.1186/s42047-021-00098-z

Abstract

BackgroundMalignant Solitary fibrous tumour (SFT) is an uncommon mesenchymal tumour with aggressive clinical behaviour as compared to its benign counterpart. There are only a handful of reports of extra-pleural malignant SFT arising from the mediastinum.Case presentationA 68-year-old male, presented with a history of cough and breathlessness for 2 weeks. Computed tomography (CT) scan revealed a large 11.6 × 11.3x18cm anterior mediastinal mass with extension to right hemithorax. The patient underwent excision of the mass after a biopsy confirmation of mesenchymal tumour. Histological examination of resection specimen revealed a spindle cell tumour with hypo and hypercellular areas, arranged in fascicular, focal storiform and hemangio-pericytomatous vasculature pattern. Moderate to marked nuclear atypia, frequent mitosis and areas of necrosis were noted. On immunohistochemistry (IHC), the tumour cells were positive for CD34, Bcl2, MIC2 (dot-like) and focally for S100 and Desmin. Although, the possibility of a malignant peripheral nerve sheath tumour with heterologous rhadomyosarcomatous differentiation (Triton tumour) was considered, however IHC for STAT6 confirmed it to be a malignant SFT. The patient developed recurrence within 1 year after surgery and despite multi-modality treatment (Re-excision, Chemotherapy and Radiotherapy) succumbed within 14 months from point of presentation.ConclusionMalignant SFT is a rare aggressive tumour that should be considered as a differential diagnosis in the mediastinum and a broad panel of IHC markers including STAT6 may be required to confirm the diagnosis.

Highlights

BackgroundA solitary fibrous tumour (SFT) is an uncommon but well-known intrathoracic fibroblastic tumour of intermediate malignant potential and was originally described as arising in relation to pleura
Malignant Solitary fibrous tumour (SFT) is an uncommon mesenchymal tumour with aggressive clinical behaviour as compared to its benign counterpart
Malignant SFT is a rare aggressive tumour that should be considered as a differential diagnosis in the mediastinum and a broad panel of IHC markers including Signal transducer and activator of transcription (STAT6) may be required to confirm the diagnosis

Summary

Background

A solitary fibrous tumour (SFT) is an uncommon but well-known intrathoracic fibroblastic tumour of intermediate malignant potential and was originally described as arising in relation to pleura. Malignant SFTs, characterized by increased cellularity, cellular pleomorphism, mitoses > 4 per 10 high power fields (HPFs) and necrosis are extremely unusual in the mediastinal region (England et al 1989). They have relatively aggressive course and inferior diseasespecific survival (De Raet et al 2008). Additional IHC for STAT6 was carried out, which showed nuclear positivity expression of moderate-intensity in approximately 70% of tumour cells (Fig. 3F). Because of the presence of an unusual histologic pattern of SFT and STAT6 positivity with necrosis, increased mitotic activity of > 4 mitoses/ 10HPF, nuclear atypia, large tumour size (20 cms), led to the classification of this tumour as a malignant giant SFT of the mediastinum. On follow-up, the patient developed local recurrence in the mediastinum (measuring 18x16cms) within 1 year after surgery and despite multi-modality treatment (Reexcision, Chemotherapy and Radiotherapy) succumbed within 14 months from point of initial presentation

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