Plexiform Fibrohistiocytic Tumor

 Most arise at dermal-subcutaneous interface



• Also lower extremity, trunk, head, and neck

• Painless, slow-growing mass or plaque

• Treatment: Wide surgical excision with negative margins

• Local recurrence in up to 40%

• Low metastatic potential (6%)




Macroscopic




• Multinodular, poorly delineated, tan-white

• Usually < 3 cm (range: 0.3-8.5 cm)


Microscopic




• Poorly circumscribed with infiltrative growth pattern
• Morphologically subdivided into 3 types (fibroblastic, histiocytic, mixed)

• Fascicles of spindled fibroblastic cells

• Nodules or aggregates of epithelioid histiocytoid cells

image Osteoclast-like giant cells common

• Multinodular and plexiform growth

• Low mitotic rate; usually no cellular pleomorphism


Ancillary Tests




• (Myo)fibroblasts SMA(+); histiocytes CD68(+) and CD163(+)

• Negative for S100, CD34, desmin, keratin, MITF


Top Differential Diagnoses




• Cellular neurothekeoma

• Giant cell tumor of soft tissue

• Fibromatosis

• Low-grade myofibroblastic sarcoma

image
Plexiform Fibrohistiocytic Tumor
Plexiform fibrohistiocytic tumor (PFHT) is an unusual, infiltrative mesenchymal neoplasm image that typically arises near the dermal-subcutaneous junction, as depicted. Tumors are characterized by fascicles or sheets of spindled fibroblasts &/or nests of histiocytoid cells in a nodular and plexiform growth pattern.


image
Infiltrative Growth in Plexiform Fibrohistiocytic Tumor
Most cases of PFHT are infiltrative and characteristically show extensions or projections of tumor into the subcutaneous adipose tissue.

image
Mixed-Type Plexiform Fibrohistiocytic Tumor
The mixed subtype of PFHT shows a complex mixture of nests image of histiocytoid cells with short fascicles of bland spindled cells image.

image
Histiocytoid Nests in Plexiform Fibrohistiocytic Tumor
The characteristic nests and aggregates of PFHT, when present, contain plump to epithelioid mononuclear histiocytoid cells. Multinucleated giant cells image may or may not be present.


TERMINOLOGY


Abbreviations




• Plexiform fibrohistiocytic tumor (PFHT)


Synonyms




• Plexiform fibrous histiocytoma


Definitions




• Rarely metastasizing dermal-subcutaneous mesenchymal neoplasm composed of variable mixture of fibroblasts and histiocyte-like cells


CLINICAL ISSUES


Epidemiology




• Incidence
image Rare

• Age
image Most common in children and young adults
– Overall wide range: 1-77 years

• Sex
image Male = female
– Female predilection in some series


Site




• Upper extremity (particularly forearm and hand)
• Also lower extremity, trunk, head and neck

• Most arise at dermal-subcutaneous interface

image May also be purely dermal or subcutaneous

– Subcutaneous tumors may involve skeletal muscle


Presentation




• Painless, slow-growing mass or plaque


Treatment




• Wide surgical excision or reexcision with negative margins

• Examination of regional lymph nodes may be warranted

• Indefinite clinical follow-up recommended

Apr 24, 2017 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Plexiform Fibrohistiocytic Tumor
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