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P.H.A.T. stands for pleomorphic hyalinizing angiectatic tumor of soft parts. This descriptive name identifies a rare tumor usually arising within the subcutaneous tissue.


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INCIDENCE <20 cases reported
AGE RANGE-MEDIAN 32-83 years


General Lobulated tumors with thin-walled ectatic vessels, often arranged in clusters, within a hyalinized stroma
Thrombosis, fibrin, and hemorrhage common
Plump spindled cells to rounded cells with prominent pleomorphism, occasional cells with bizarre nuclei
Intranuclear inclusions common
MF sparse
Pleomorphic hyalinizing angiectatic tumor of soft parts: case report and literature review.

El-Tal AE, Mehregan D.

Department of Dermatology, American University of Beirut, Beirut, Lebanon.

J Cutan Pathol. 2006 May;33(5):361-4. Abstract quote  

Pleomorphic hyalinizing angiectatic tumor (PHAT) of soft parts is a rare soft tissue neoplasm. Few cases have been reported in the literature thus far. PHAT is a spindle cell neoplasm with a prominent vascular component which displays some features of both neurilemoma and malignant fibrous histiocytoma.

Lesions typically occur on the lower extremities of adults, however, lesions in other anatomic locations have been described.

In this paper, we report a 60 years old female with PHAT of the right foot and review the current literature.
Pleomorphic hyalinizing angiectatic tumor: analysis of 41 cases supporting evolution from a distinctive precursor lesion.

Folpe AL, Weiss SW.

From the Department of Pathology and Laboratory Medicine Emory University, Atlanta, GA.

Am J Surg Pathol. 2004 Nov;28(11):1417-25. Abstract quote  

The pleomorphic hyalinizing angiectatic tumor (PHAT) is a rare, low-grade neoplasm that features atypical stromal cells containing hemosiderin, partially thrombosed ectatic vessels with circumferential hyalinization, and a variable inflammatory infiltrate.

Over the years, we have occasionally observed a monomorphic partially myxoid spindle cell component (provisionally termed "early PHAT") co-existing with classic PHAT. In some instances, this monomorphic lesion occurs by itself, suggesting an early stage in the evolution of PHAT. To explore this hypothesis and to better define the long-term behavior of PHAT, we have reviewed our experience with these lesions.

Forty-one cases were identified from consultation files. They occurred chiefly in adults (median 51 years, range 10-79 years) of either sex (23 female, 18 male), ranged from 0.3 to 19.7 cm (median 5.6 cm), and involved the subcutis of the ankle/foot (N = 15), leg (N = 10), thigh (N = 6), and other sites. Thirteen tumors had been present for more than 1 year prior to biopsy. Fifteen tumors consisted entirely of typical PHAT. Twelve cases conformed to "early PHAT," lacked fully developed features of PHAT, and showed instead short fascicles of hemosiderin-stippled spindled cells that infiltrated fat and surrounded congeries of small, damaged vessels. With close scrutiny, all contained rare pleomorphic cells with intranuclear pseudo-inclusions, as seen in typical PHAT. Fourteen cases contained both classic and early PHAT, in variable proportions. Follow-up was available in 18 patients (mean 84 months, median 52 months; range 13-420 months). Six of 18 patients developed recurrences, 1 with classic PHAT, 1 with mixed early-classic PHAT, and 4 with early PHAT. Following resection, 16 are disease free and 2 have persistent disease. None has developed metastasis.

Based on the histologic overlap between early and classic PHAT, the presence of early PHAT at the periphery of classic PHAT, and the admixture of both patterns within the same tumor, we conclude that early PHAT represents a precursor lesion for PHAT. It appears essentially identical to the lesion termed "hemosiderotic fibrohistiocytic lipomatous lesion," supporting the notion that the latter is a neoplastic rather than a reactive lesion. PHAT should be considered mesenchymal tumors of intermediate malignancy, given their high rate of (sometimes aggressive) local recurrence.
Pleomorphic hyalinizing angiectatic tumor of soft parts: report of a case and review of the literature.

Fujiwara M, Yuba Y, Wada A, Ozawa T, Tanaka T.

Department of Plastic and Reconstructive Surgery, Tenri Hospital, Kyoto, Japan.

J Dermatol. 2004 May;31(5):419-23. Abstract quote  

We present the case of a 69-year-old man with a subcutaneous pleomorphic hyalinizing angiectatic tumor of soft parts on the back. In addition to its rare localization, it showed unique clinical features of an exceptionally long history.

Histological characteristics of this tumor showed thin-walled angiectatic blood vessels lined with a thick eosinophilic and hyalinotic amorphous material. Tumor cells are composed of pleomorphic cells.

It was surgically removed, and there was no recurrence by 11 months postoperatively.
Pleomorphic hyalinizing angiectatic tumor of soft parts: a case report and literature review.

Matsumoto K, Yamamoto T.

Division of Pathology, Second Hospital of Nippon Medical School, Kawasaki, Japan.

Pathol Int. 2002 Oct;52(10):664-8 Abstract quote.  

Pleomorphic hyalinizing angiectatic tumor (PHAT) is a rare, recently recognized neoplasm occurring predominantly in the subcutaneous tissue of the lower limbs of adults. We report a case of PHAT in an 83-year-old woman who presented with a 5.0 x 5.0 x 2.0 cm mass in the soft part of her left thigh.

Histologically, the tumor was well circumscribed by a thin fibrous capsule and predominantly composed of fusiform cells with eosinophilic cytoplasm and round-to-oval or pleomorphic nuclei. The tumor cells resembled those of malignant fibrous histiocytoma, but differed from them by less prominent mitotic figures. Immunohistochemically, the tumor cells were diffusely and strongly positive for CD34; partially positive for vimentin and CD99 (MIC-2); and negative for epithelial and non-epithelial markers. Ultrastructurally, the tumor cells had pleomorphic cytoplasm and nucleus. Intermediate-sized cytoplasmic filaments were observed in a few tumor cells, but neurosecretory-type granule-like intracytoplasmic organelles were not seen.

These findings suggest that this tumor is derived from stromal fibroblast, such as solitary fibrous tumors or giant cell angiofibroma.
Pleomorphic hyalinizing angiectatic tumor of soft parts. A low-grade neoplasm resembling neurilemoma.

Smith ME, Fisher C, Weiss SW.

Department of Histopathology, University College London Medical School, England.

Am J Surg Pathol. 1996 Jan;20(1):21-9. Abstract quote  

Fourteen examples of an unusual mesenchymal tumor characterized by sheets and fascicles of mitotically inactive, hemosiderin-stippled, spindled, and pleomorphic cells, situated around an angiectatic vasculature, are described.

The 14 tumours developed in eight women and six men (aged 32-83 years) and ranged in size from 2.3 to 8 cm. Eleven cases presented in the subcutaneous tissues, of which eight were located in the lower extremity. All featured prominent clusters of thin-walled ectatic vessels surrounded by perivascular hyaline material representing a combination of fibrin and collagen. In three cases the perivascular hyalinization was so extensive that it constituted more than half of the total tumor area. The tumor cells were similar to those of malignant fibrous hystiocytoma but differed from them by the presence of prominent intranuclear cytoplasmic inclusions, the extreme scarcity of mitotic figures, and the occasional presence of CD-34 expression. These tumors also shared several features with neurilemomas, such as their unusual vasculature, intranuclear cytoplasmic inclusions, lack of mitotic figures, and abundance of mast cells. They could be distinguished from neurilemomas, however, by the usual presence of infiltrative margins and the absence of S-100 protein.

Follow-up information on eight patients (6 months to 25 years) indicated recurrences in four cases, with one of the three patients experiencing numerous recurrences over a 25-year period. No patient has developed metastases, however.

We suggest that this tumor is a low-grade sarcoma of uncertain lineage in which the vascular changes are, in part, reflective of its slow growth.


Special stains  
Immunoperoxidase S100 negative
50% positive for CD34
Negative for CD31, EMA, desmin, SMA
Pleomorphic hyalinizing angiectatic tumor of soft parts: immunohistochemical study including the expression of vascular endothelial growth factor.

Groisman GM, Bejar J, Amar M, Ben-Izhak O.

Department of Pathology, Hillel-Yaffe Medical Center, Hadera, Bnai-Zion Medical Center, Haifa, Israel.

Arch Pathol Lab Med. 2000 Mar;124(3):423-6. Abstract quote

We report morphologic, flow cytometric, and immunohistochemical findings in two cases of pleomorphic hyalinizing angiectatic tumor of soft parts.

Both patients were middle-aged women with subcutaneous lesions located in the lower extremity. The tumors consisted of sheets of spindled and pleomorphic cells with frequent intranuclear pseudoinclusions associated with clusters of ectatic vessels surrounded by prominent perivascular hyaline material. Numerous, nonhyalinized vessels were also present, mostly in the peripheral areas of the lesions. Some of these vessels had their walls permeated by numerous small capillaries. Immunostaining for vascular endothelial growth factor (VEGF), a secreted protein that has been implicated in tumor-associated angiogenesis, demonstrated positive staining in both tumoral and endothelial cells.

Tumor cells were also reactive to vimentin and CD34. Focal positivity for CD99 and factor XIIIa was also present. Flow cytometry yielded a diploid DNA histogram with S-phase fraction of 7%.

Our findings corroborate those from previously reported cases. They further suggest that angiogenesis and the angiogenic factor VEGF may play a role in the development of this peculiar tumor.
Pleomorphic hyalinizing angiectatic tumor of soft parts: immunohistochemical case study shows cellular composition by CD34+ fibroblasts and factor XIIIa+ dendrophages.

Silverman JS, Dana MM.

Department of Pathology and Laboratory Medicine, Southampton Hospital, New York 11969, USA.

J Cutan Pathol. 1997 Jul;24(6):377-83. Abstract quote  

We report immunomorphologic observations on a pleomorphic hyalinizing angiectatic tumor of soft parts (PHAT), a rare tumor recently described by Smith, Fisher, and Weiss.

A 2 cm skin-covered, grossly lobulated, firm, yellow-tan, focally hemorrhagic tumor was excised from the dorsum of a 59-year-old woman's right foot. It infiltrated dermis and subcutis and entrapped skin adnexae.

The tumor microscopically resembled both a pleomorphic malignant fibrous histiocytoma and a neurilemoma with fascicular spindle cell pattern, pleomorphic tumor giant cells, and focal congeries of ectatic, fibrinous, and slightly hyalinized vessels. Tumour cells produced abundant reticulin but collagenous sclerosis was minimal. Mast cells were numerous. Pleomorphic cells, some phagocytic, had intranuclear vacuolar inclusions and many cells had large pale cytoplasmic globular inclusions. Most tumor cells expressed vimentin and CD34, including pleomorphic cells. Factor XIIIa stained focally 20-40% of the spindle cells. S-100 and cytokeratin were negative and actin and desmin stained only vessel myopericytes. The Ki 67 index was 3% with mostly large CD34+ cells and a few smaller FXIIIa+ cells in the cycling fraction.

We conclude that PHAT is a fibrohistiocytic tumor probably derived from proliferating microvascular CD34+ dendritic cells and FXIIIa+ dendrophage cell subsets. Possible interactions between these cell types deserve further study in PHAT and other fibrohistiocytic tumors.
Pleomorphic hyalinizing angiectatic tumor of soft parts: ultrastructural analysis of a case with original features.

Capovilla M, Birembaut P, Cucherousset J, Ploton D, de Saint-Maur PP, Flejou JF, Lesec G.

Laboratoire Pol-Bouin, Hopital Maison-Blanche, Reims, France.

Ultrastruct Pathol. 2006 Jan-Feb;30(1):59-64. Abstract quote  

Pleomorphic hyalinizing angiectatic tumor, a rare neoplasm of uncertain lineage resembling malignant fibrous histiocytoma and schwannoma, was first described in 1996 by M. E. F. Smith et al. (Am Surg Pathol. 20:21-29). To date, less than 100 cases have been reported in the international literature.

It occurs in subcutaneous and intramuscular soft tissues of extremities or trunk in adults without sex predilection. All lesions are composed of sheets and fascicles of spindled and pleomorphic cells associated with clusters of thick-walled ectatic vessels surrounded by a perivascular hyaline material and inflammatory cells such as mast cells. About one-half of these neoplasms express CD34. No patient has developed metastases but occasional local recurrences are possible. This tumor of uncertain lineage is suggested to be an aggressive locally growing low-grade sarcoma. Only 3 cases were previously studied by electron microscopy and appeared to consist of primitive fibroblastic cells.

The authors report histological and ultrastructural characteristics of a new case of PHAT excised from the right buttock of a 66-year-old man with the presence of ganglion-like cells, a feature that has not been previously reported, and unusual central ischemic necrosis. The features of this case are suggestive of a fibroblastic origin.


Recurrence 4/8 with recurrence
Metastasis None to date

Am J Surg Pathol 1996;20:21-29
Henry JB. Clinical Diagnosis and Management by Laboratory Methods. Twentieth Edition. WB Saunders. 2001.
Rosai J. Ackerman's Surgical Pathology. Ninth Edition. Mosby 2004.
Sternberg S. Diagnostic Surgical Pathology. Fourth Edition. Lipincott Williams and Wilkins 2004.
Robbins Pathologic Basis of Disease. Seventh Edition. WB Saunders 2005.
DeMay RM. The Art and Science of Cytopathology. Volume 1 and 2. ASCP Press. 1996.
Weedon D. Weedon's Skin Pathology Second Edition. Churchill Livingstone. 2002
Fitzpatrick's Dermatology in General Medicine. 6th Edition. McGraw-Hill. 2003.
Weiss SW and Goldblum JR. Enzinger and Weiss's Soft Tissue Tumors. Fourth Edition. Mosby 2001.

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Last Updated May 15, 2006

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