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Plexiform Fibrohistiocytic Tumour

Plexiform fibrohistiocytic tumor is a rare dermal and subcutaneous neoplasm showing plexiform architecture and biphasic morphology, composed of nodules of histiocytoid cells and bundles of myofibroblastic spindle cells.

Symptoms & Causes

Introduction

Plexiform fibrohistiocytic tumor is a rare dermal and subcutaneous neoplasm characterized by plexiform architecture and a biphasic composition of histiocytoid and spindle cells.

Reference
WHO Classification of Tumours Editorial Board. Soft tissue and bone tumours [Internet]. Lyon (France): International Agency for Research on Cancer; 2020 [cited 2024 09 11]. (WHO classification of tumours series, 5th ed.; vol. 3). Available from: https://tumourclassification.iarc.who.int/chapters/33.

Related Terminology
None

Subtype(s)
None

Symptoms

The tumors present as slow-growing, ill-defined plaques and nodules, typically measuring 1–3 cm in diameter.

Localization

There is a strong predilection for the upper limbs followed by the lower limbs. The trunk and the head and neck area are less often affected.

Epidemiology

The age range is wide, but children and young adults are typically affected, with a median age of 14.5–20 years and an equal sex distribution.

Etiology

Unknown

Diagnosis & Treatment

Staging

Not clinically relevant

Pathogenesis

Unknown

Macroscopic Appearance

These tumors form a nondescript mass at the dermal–subcutaneous junction, usually < 3 cm in size.

Histopathology

Plexiform fibrohistiocytic tumors are centered at the dermal–subcutaneous junction. They show an infiltrative architecture with overall plexiform outlines and may extend into skeletal muscle. The tumors are composed of small nodules of histiocytoid cells and osteoclast-like multinucleated giant cells, surrounded by fascicles of spindle cells in varying proportions. There may be hemorrhage, haemosiderin deposition, and a chronic inflammatory infiltrate. Lymphovascular invasion can rarely be seen. Additional rare findings include myxoid or hyalinized stromal changes and metaplastic bone formation. By immunohistochemistry, the spindle cells express SMA.

Cytology

Not clinically relevant

Prognosis and Prediction

Plexiform fibrohistiocytic tumor is associated with a risk for local recurrence ranging from 12.5% to 37.5% and rare lymph node metastasis. Distant metastasis to the lung is exceptional.

Clinical Features

Diagnostic Molecular Pathology

Not clinically relevant

Essential and Desirable Diagnostic Criteria

Essential: plexiform architecture; involvement of dermis and/or subcutaneous adipose tissue; nodules composed of histiocytoid epithelioid cells and osteoclast-like giant cells; fascicles of myofibroblastic spindle cells.

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