Plexiform Fibrohistiocytic Tumor: An Updated Review.

Plexiform fibrohistiocytic tumor (PFHT) is a rare locally aggressive and rarely metastasizing mesenchymal neoplasm that most commonly arises in the upper extremities of children and young adults. It typically presents as a small, slow-growing, painless, dermal or subcutaneous mass. Magnetic resonance imaging (MRI) often reveals a plaque-like or infiltrative lesion with intermediate signal intensity on T1-weighted sequences and high signal intensity on T2-weighted sequences. Contrast-enhanced MRI demonstrates moderate or avid enhancement. Histologically, PFHT is characterized by a multinodular or plexiform proliferation of a variable admixture of histiocyte-like cells, osteoclast-like giant cells and elongated spindle cells. Immunohistochemically, the histiocyte-like and osteoclast-like giant cells express CD68, CD163 and CD11c, whereas the spindle cells are focally positive for smooth muscle actin. Most notably, cyclin D1 immunostaining demonstrates nuclear expression in the histiocyte-like and osteoclast-like giant cells as well as spindle cells. Wide local excision with long-term follow-up is generally considered optimal management for conventional cases. This review provides an updated overview of the clinical, radiological, histological, immunohistochemical, cytogenetic and molecular genetic features of PFHT and discusses the differential diagnosis of this enigmatic neoplasm.