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A case of a large solitary fibrous tumor in the thigh, displaying NAB2ex4-STAT6ex2 gene fusion

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A Correction to this article was published on 16 October 2021

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Abstract

A solitary fibrous tumor (SFT) is documented in several body sites. However, there are few reports on the radiological and corresponding histopathological, including immunohistochemical, features of SFT in the lower extremities. A 58-year-old male presented with a lump in his right thigh of 6 months duration. Plain radiograph revealed a soft tissue lesion in his right thigh, involving the adjacent mid-diaphysis and showing focal cortical thickening and calcification. Magnetic resonance imaging scans displayed two well-defined, T1-isointense and T2 heterogeneously hyperintense lesions, measuring together 15 cm in the intermuscular plane and the juxtacortical location along the mid-diaphyseal region of the right femur. Radiologically, the differential diagnoses considered were undifferentiated pleomorphic sarcoma and synovial sarcoma. Microscopic examination of the core biopsy and the resected tumor revealed a tumor composed of cells with oval to spindle-shaped nuclei in a variably collagenized stroma, including hyalinized blood vessels and focal dystrophic calcification. Mitotic figures were 4/10 high power fields. Immunohistochemically, the tumor cells were positive for CD34, BCL2, and STAT6. Diagnosis of malignant SFT was offered. The tumor displayed NAB2ex4-STAT6ex2 gene fusion on molecular testing. This constitutes a relatively uncommon case report of a large SFT in the thigh, including its radiological and pathological features, confirmed by STAT6 immunostaining. An SFT should be considered in cases of slow-growing, well-defined soft tissue tumors, which are isointense on T1 and heterogeneously hyperintense on T2-weighted sequences, and display calcification and cortical thickening of the adjacent bones. Various differential diagnoses and their treatment-related implications in such cases are discussed herewith.

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Authors and Affiliations

  1. Department of Surgical Pathology, (Bone and Soft Tissues) Disease Management Group, Tata Memorial Hospital (TMH), Homi Bhabha National Institute (HBNI) University, Room Number 818, 8th Floor, Annex Building, Dr E.B. Road, Parel, 400012, Mumbai, India

    Bharat Rekhi

  2. Division of Molecular Pathology and Translational Medicine, Tata Memorial Hospital (TMH), Homi Bhabha National Institute (HBNI) University, Parel, Mumbai, India

    Bharat Rekhi & Prachi Bapat

  3. Department of Radiodiagnosis (Bone and Soft Tissues) Disease Management Group, Tata Memorial Hospital (TMH), Homi Bhabha National Institute (HBNI) University, Mumbai, India

    Nivedita Chakrabarty

  4. Department of Surgical Oncology (Bone and Soft Tissues), Disease Management Group, Tata Memorial Hospital (TMH), Homi Bhabha National Institute (HBNI) University, Parel, Mumbai, India

    Prakash Nayak

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  1. Bharat Rekhi
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  2. Prachi Bapat
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  4. Prakash Nayak
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Correspondence to Bharat Rekhi.

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Rekhi, B., Bapat, P., Chakrabarty, N. et al. A case of a large solitary fibrous tumor in the thigh, displaying NAB2ex4-STAT6ex2 gene fusion. Skeletal Radiol 50, 2299–2307 (2021). https://doi.org/10.1007/s00256-021-03829-1

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  • DOI: https://doi.org/10.1007/s00256-021-03829-1

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