plexiform fibrohistiocytic tumor

Definition: Plexiform fibrohistiocytic tumor is a low-grade malignant myofibroblastic tumor of children, adolescents and young adults.

Synopsis

 most occur in the upper extremity (63.1-69%)
 female predominance
 ill-defined, infiltrative mass of the subcutaneous adipose tissue
 possible extension in the dermis and/or skeletal muscle
 multinodular or plexiform proliferation of mononuclear histiocyte-like cells
 spindle fibroblast-like cells
 multinucleated osteoclast-like giant cells

 three distinct growth patterns :

• fibrohistiocytic (36%)
• fibroblastic (32%)
• mixed (32%)

 cellular atypia and pleomorphism rare or absent; usually less than 3 mitoses/10 HPF
 rare vascular involvement reported
 hyaline collagen
 rare myxoid changes
 +/- mucin deposits
 frequent foci of microhemorrhage
 possible osseous metaplasia
 occasional chronic inflammatory infiltrate in or around the nodules

Immunohistochemistry

 spindle cells usually express SMA and histiocyte-like cells occasionally
 histiocytic and osteoclast-like cells express CD68, spindle cells oly rarely
 unusual positivity for alpha-1-antitrypsin or alpha-1-antichymotrypsin
 occasional faint and focal CD34 and CD57 staining
 S100, desmin, cytokeratin, factor-VIII-related protein, lyzosyme, factor XIIIa negative

Variants

 myxoid plexiform fibrohistiocytic tumour (12428852)
 metastatic forms (9130995)
 devoid of osteoclast-like giant cells (12357200)

Cytogenetics

 t(8;?) (p22;?) (2164878)
 t(4;15)(q21;q15) (9973942)

Differential diagnosis

 granulomatous inflammation

• granuloma annulare

 fusiform cell soft tissue tumors

• dermatofibrosarcoma protuberans
• fibrous hamartoma of infancy
• plexiform neurofibroma
• soft tissue giant cell tumor
• infantile myofibromatosis
• cellular neurothekeoma
• well-differentiated fibrosarcoma
• congenital dermatofibroma protuberans
• nodular fasciitis

 plexiform tumors

• plexiform neurofibroma

Prognosis

 frequent recurrence (12.5-40%) within 1-2 years after original diagnosis
 extremely rare lymph node metastases
 extremely rare pulmonary metastases

Cytogenetics

 del(X)(q13) mosaicism (21261704)

See also

 myofibroblastic tumors
 fusiform cell tumors

References

 Plexiform Fibrohistiocytic Tumor with Molecular and Cytogenetic Analysis. Leclerc-Mercier S, Pedeutour F, Fabas T, Glorion C, Brousse N, Fraitag S. Pediatr Dermatol. 2011 Jan 25. PMID: 21261704

 Neurothekeoma and Plexiform Fibrohistiocytic Tumor: Mere Histologic Resemblance or Histogenetic Relationship? Jaffer S, Ambrosini-Spaltro A, Mancini AM, Eusebi V, Rosai J. Am J Surg Pathol. 2009 Apr 1. PMID: 19342943

 Leclerc S, Hamel-Teillac D, Oger P, Brousse N, Fraitag S. Plexiform fibrohistiocytic tumor: three unusual cases occurring in infancy. J Cutan Pathol. 2005 Sep;32(8):572-6. PMID: 16115057

 Remstein ED, Arndt CA, Nascimento AG. Plexiform fibrohistiocytic tumor: clinicopathologic analysis of 22 cases. Am J Surg Pathol. 1999 Jun;23(6):662-70. PMID: 10366148

 Salomao DR, Nascimento AG. Plexiform fibrohistiocytic tumor with systemic metastases: a case report. Am J Surg Pathol. 1997 Apr;21(4):469-76. PMID: 9130995

 Zelger B, Weinlich G, Steiner H, Zelger BG, Egarter-Vigl E. Dermal and subcutaneous variants of plexiform fibrohistiocytic tumor. Am J Surg Pathol. 1997 Feb;21(2):235-41. PMID: 9042292

 Thomazy V, Nagy A, Gal I, Nemes Z. Plexiform fibrohistiocytic tumour with novel phenotypic features. Histopathology. 1994 Aug;25(2):165-9. PMID: 7982679

 Enzinger FM, Zhang RY. Plexiform fibrohistiocytic tumor presenting in children and young adults. An analysis of 65 cases. Am J Surg Pathol. 1988 Nov;12(11):818-26. PMID: 2847569

 Salamanca J, Rodriguez-Peralto JL, Garcia de la Torre JP, Lopez-Rios F. Plexiform fibrohistiocytic tumor without multinucleated giant cells: a case report.
Am J Dermatopathol. 2002 Oct;24(5):399-401. PMID: 12357200