Soft Tissue Tumors - Plexiform fibrohistiocytic tumor

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Soft Tissue Tumors

Fibrohistiocytic tumors

Plexiform fibrohistiocytic tumor

Reviewer: Vijay Shankar, M.D. (see Reviewers page)
Revised: 21 December 2012, last major update August 2012
Copyright: (c) 2003-2012, PathologyOutlines.com, Inc.

General
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● Dermal or subcutaneous, plexiform or multinodular proliferation of fibrohistiocytic cells and osteoclast-like giant cells with chronic inflammatory infiltrate

Terminology
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● First described in 1988 (Am J Surg Pathol 1988;12:818)
● Also called plexiform fibrous histiocytoma
● May have common histogenesis with cellular neurothekeoma (Am J Surg Pathol 2009;33:905)

Epidemiology
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● Usually children and young adults, 80% female

Clinical features
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● Small, slow growing dermal or subcutaneous mass, upper extremity (65%) or lower extremity (27%), rarely head and neck (Dermatol Sinica 2010;28:117 (pdf))

Case reports
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● 3 year old child whose tumor lacked osteoclast-like giant cells (Am J Dermatopathol 2002;24:399)
● 5 year old boy with bilateral thigh tumors (J Chinese Oncol Soc 2009;25:153)
● 6 year old boy with small perioral tumor (Eur J Dermatol 2004;14:118)
● 17 year old girl with nasal tumor and nodal metastasis (Dermatol Sinica 2010;28:117)
● 21 year old woman with mass on back (Indian J Pathol Microbiol 2008;51:245)
● 24 year old woman with supraclavicular myxoid tumor without giant cells (Arch Pathol Lab Med 2004;128:931)
● 29 year old woman with occipital mass (Case of the Week #180)
● 39 year old woman with recurrent tumor (Univ Pittsburgh Case #316)

Treatment and prognosis
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● Low grade malignant behavior
● After excision, recurs locally, rarely has nodal or pulmonary metastases (Am J Surg Pathol 1999;23:662)

Gross description
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● Multinodular, poorly circumscribed, firm, dermal or subcutaneous, 3 cm or less

Micro description
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● Deep dermal or subcutaneous tumor with ray like extension into skeletal muscle or adipose tissue
● Overlying epidermis and dermis are usually normal
● Plexiform or multinodular proliferation of fibrohistiocytic cells with minimal atypia plus osteoclast-like giant cells and chronic inflammatory infiltrate
● Nodules or clusters are interconnected in characteristic plexiform arrangement
● Prominent dilated vessels; more sclerotic than MFH
● Often hemorrhage and hemosiderin
● Vascular invasion in 10-20%
● Usually 0-2 MF/10 HPF, no necrosis
● Subtypes are fibrohistiocytic (histiocyte-like cells and giant cells), fibroblastic (fibroblast-like cells) and mixed

Micro images
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Subcutaneous proliferation of bland fibrous tissue which radiates outward from center of lesion

Most tumors have nodules of histiocyte-like cells and giant cells, also fibrous tissue and hemorrhage

Histiocyte-like cells have pale staining cytoplasm; giant cells are also present

Nodules may be composed of cells with elongated nuclei

Tumor with nodules and fibrous tissue

Fibrous tissue may resemble desmoid fibromatosis

Axillary lymph node has multiple plexiform nodules within and outside the node

Nodules are composed of plump cells and multi-nucleated giant cells

Various images

Case of Week #180: H&E, bottom row - CD68 and smooth muscle actin

12 year old girl with upper arm lesion

Virtual slides
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Plexiform fibrohistiocytic tumor

Cytology description
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● Plump fibroblastic cells and histiocyte-like cells within a finely granular myxoid background
● Also osteoclast-like giant cells (Acta Cytol 1999;43:867)

Cytology images
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Various images

Positive stains
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● Vimentin, CD68 (giant cells and mononuclear histiocyte-like cells), smooth muscle actin (fibroblast-like cells, Histopathology 1991;19:503)
● Rarely alpha-1-antitrypsin and alpha-1-antichymotrypsin

Negative stains
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● S100, keratin, CD45, Factor VIII, desmin

Electron microscopy description
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● Resembles myofibroblasts, fibroblasts and undifferentiated cells

Differential diagnosis
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● Benign fibrous histiocytoma: older patients, prominent foam cells, no plexiform extensions of fibrous tissue, no nodules of histiocyte-like cells, no multinucleated giant cells
● Cellular neurothekeoma: uniform population of epithelioid cells, no distinct nodules of histiocytoid cells or osteoclast-like giant cells (Am J Surg Pathol 2007;31:329), podoplanin+ (Am J Dermatopathol 2009;31:137)
● Fibromatosis: centered in muscle, diffusely infiltrative, no nodules
● Fibrous hamartoma of infancy: immature cells present, also myxoid stroma
● Giant cell tumor of soft tissue: infiltrative nodules of mixed giant cells and spindle cells, frequent mitotic figures
● Neurofibroma: no distinct nodules, S100+

Additional references
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● Ann Diagn Pathol 2007;11:313, Arch Pathol Lab Med 2007;131:1135, Stanford University

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