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pleomorphic hyalinizing angiectatic tumor

Tuesday 7 February 2006

Pleomorphic hyalinizing angiectatic tumor of soft parts, PHAT

Definition: Pleomorphic hyalinizing angiectatic tumor of soft parts (PHAT) is an uncommon tumour occurring most often in subcutaneous tissues of the lower extremity and characterized by notable pleomorphism in the absence of mitotic activity. These lesions contain thin-walled dilated vessels showing prominent fibrinoid change in their walls.

Rare, locally aggressive tumor of uncertain differentiation, adult tumor, M=F ratio, subcutaneous location and rarely deep soft tissue. CD34 positive



Histologically, typical PHAT is characterized by spindle and pleomorphic cells associated with an angiectatic vasculature. The neoplastic cells often express vimentin and CD34, and may be positive for CD99 and VEGF. The low MIB-1 index and the absence of aneuploidy in PHAT indicate a non-malignancy.

This tumor can be considered as a borderline neoplasm because of its aggressive behaviour, and suggest wide local resection with tumor-free margin for the treatment of the disease.


- grossly lobulated, firm, yellow-tan, focally hemorrhagic tumor
- dermohypodermal infiltration
- bizarre spindle cells
- hyalinized ectatic vessels
- fascicular spindle cell pattern
- pleomorphic tumor giant cells

  • some phagocytic pleomorphic cells
  • intranuclear vacuolar inclusions
  • large pale cytoplasmic globular inclusions

- focal congeries of ectatic, fibrinous, and slightly hyalinized vessels
- abundant reticulin
- minimal collagenous sclerosis
- numerous mast cells were


- vimentin+
- CD34+ (CD34+ dendritic cells)
- +/- Factor XIIIa+ (FXIIIa+ dendrophage cell)

- S-100-
- cytokeratin-


PHAT is a fibrohistiocytic tumor probably derived from proliferating microvascular CD34+ dendritic cells and FXIIIa+ dendrophage cells from microvascular units.

Differential diagnosis

- hyalinizing tumors

- pleomorphic malignant fibrous histiocytoma (MFH)
- neurilemmoma

Molecular biology

- TGFBR3 and MGEA5 rearrangements in :

See also

- microvascular unit

  • microvascular CD34+ dendritic cells
  • microvascular FXIIIa+ dendrophage cells

- fibrohistiocytic tumors
- CD34+ fibroblasts
- FXIIIa+ macrophages

- CD34+ tumors

Open access references

- Clinicopathologic features of pleomorphic hyalinizing angiectatic tumor of soft parts. Ke Q, Erbolat, Zhang HY, Bu H, Li S, Shi DN, Yang GH, Chen HJ, Wei B. Chin Med J (Engl). 2007 May 20;120(10):876-81. PMID: 17571460 [Free]


- Folpe AL, Weiss SW. Pleomorphic hyalinizing angiectatic tumor: analysis of 41 cases supporting evolution from a distinctive precursor lesion. Am J Surg Pathol. 2004 Nov;28(11):1417-25. PMID: 15489645

- Fujiwara M, Yuba Y, Wada A, Ozawa T, Tanaka T. Pleomorphic hyalinizing angiectatic tumor of soft parts: report of a case and review of the literature. J Dermatol. 2004 May;31(5):419-23. PMID: 15187312

- Silverman JS, Dana MM. Pleomorphic hyalinizing angiectatic tumor of soft parts: immunohistochemical case study shows cellular composition by CD34+ fibroblasts and factor XIIIa+ dendrophages. J Cutan Pathol. 1997 Jul;24(6):377-83. PMID: 9243366

- Smith ME, Fisher C, Weiss SW. Pleomorphic hyalinizing angiectatic tumor of soft parts. A low-grade neoplasm resembling neurilemoma. Am J Surg Pathol. 1996 Jan;20(1):21-9. PMID: 8540605