Fibrous Histiocytoma
Key Points
Fibrous histiocytoma (FH) is a soft-tissue tumor characterized by a proliferation of spindle-shaped cells, usually admixed with inflammatory cells
It is believed to originate from a primitive mesenchymal cell with differentiation into fibroblast or histiocyte-like components
This tumor can occur in any part of the body and can be benign or malignant
Eyelid lesions usually present as a slow-growing, firm, painless, subcutaneous, or tarsal nodular mass, ranging from 4 mm to 1.5 cm in diameter
Rarely they can be localized to the bulbar conjunctiva where they present as slow-growing, painless, vascular, yellow to pink elevated nodules that occasionally can infiltrate the cornea
Local surgical excision is the treatment of choice
Radiation therapy may be helpful as an adjuvant treatment in certain settings
Local recurrence following surgical excision of benign FH has been reported between 5% and 11%
Rates of local recurrence for malignant fibrous histiocytoma range from 25% to 75% with a 5-year overall survival rate of 48%
Fibrous histiocytoma (FH) is a common soft-tissue tumor characterized by a proliferation of spindle-shaped cells, usually admixed with inflammatory cells.1,2 Lesions previously included under this name can be cutaneous or subcutaneous in location. In recent years, cutaneous tumors located in the dermis are more commonly referred to as dermatofibroma.3,4 Deeper, subcutaneous tumors of this type are termed FH. These are less common than cutaneous forms and generally are larger and better circumscribed.2,5,6,7
FH was first described in 1961 by Kauffman and Stout.8 It frequently involves muscular, fibrous, and fatty tissues.9 Ocular involvement is infrequent and primarily limited to the orbit where it represents 0.5% of all benign orbital tumors and is considered to be the most common primary mesenchymal tumor of the orbit seen in adults.10,11 Rarely, these tumors can arise in the conjunctiva, episclera, choroid, and lacrimal sac.12,13,14,15,16,17,18,19,20,21,22,23,24,25 Its occurrence in the eyelid is rare.4,19,26,27,28,29,30,31,32,33,34,35,36,37
Malignant fibrous histiocytoma (MFH) was described in 1961 by Kauffman and Stout8 and has been considered to be the most common adult soft-tissue sarcoma.38,39 However, major advances in immunohistochemistry during the past several decades have led to a reclassification of many tumors once included under MFH,40 so that nearly three-fourths of tumors previously diagnosed as MFH are now considered to represent alternative diagnoses.41 Although controversial, some studies have indicated that the most probable cells of origin for MFH may be primitive mesenchymal or fibroblastic cells, rather than histiocytic cells. As a result, MFH is now frequently referred to as pleomorphic undifferentiated sarcoma.
MFH develops in males in approximately two-thirds of cases, arising most commonly during the sixth and seventh decades of life.42,43 It most commonly occurs in the head and neck region, trunk, extremities, and retroperitoneum, but very rarely is seen in the eyelid.37,44,45,46,47,48 It has a high potential for local muscle, perineural, and blood vessel invasion, and to progress to distant metastasis.
Etiology and Pathogenesis
FH is a soft-tissue neoplasm with both fibrocytic and histiocytic components. The tumor was initially thought to arise from two different cell types,8 but it is now believed to originate from a primitive mesenchymal cell with differentiation into fibroblast or histiocyte-like components.10 This tumor can occur in any part of the body and can be benign or malignant.8 The orbit is the most common ocular site.10 Case reports have described the occurrence of conjunctival FHs in individuals with a history of trauma, leukemia, chemotherapy, prednisone use, radiation, rheumatoid arthritis, and xeroderma pigmentosum.49,50 There is also an association between systemic lupus erythematosis, multiple dermatofibromas, and FH in extraocular locations.51
Angiomatoid FH is a rare form with intermediate biologic potential most often arising in the extremities of children and young adults. Only one case has been described in the eyelid.33 Genetic abnormalities have been described in angiomatoid FH, associated with three characteristic gene fusions, EWSR1-CREB1, EWSR1-ATF1, and, rarely, FUS-ATF1. Angiomatoid FH is now recognized in an increasing number of sites and is known to display a variety of unusual histologic features.52,53,54
For MFH, previous ionizing radiation therapy (RT) appears to be a risk factor in some cases.55,56,57 It is the most commonly diagnosed sarcoma in patients with prior radiation exposure in the head or neck region, and patients with radiation-associated tumors in this region have a worse prognosis than those with tumors not associated with prior RT.58,59,60,61 Genetic alterations in MFH include the p53 gene,62 as well as H- and K-ras gene activation.63
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