[486] Metastasizing “Benign” Fibrous Histiocytoma: A Clinicopathologic Study of 15 Cases

Leona A Doyle, Christopher DM Fletcher. Brigham and Women's Hospital & Harvard Medical School, Boston, MA

Background: Cutaneous fibrous histiocytoma (FH) is considered a benign tumor; however, certain types of FH have been shown to have a tendency for local recurrence and there are a few reported cases of metastasis.
Design: 15 cases of morphologically "benign" FH with locoregional or distant metastasis were identified in consult files. Pathologic features and clinical outcome of primary, recurrent and metastatic tumors were evaluated.
Results: 9 patients were male and 6 female; mean age was 42 years (range 3-68). 6 tumors arose on the trunk, 5 on the lower limbs, 2 on the neck and 1 on the upper limb. Primary site in 1 case was unknown. 14 primary tumors involved the dermis; 6 extended into subcutis. Tumor size ranged from 1 to 5cm (mean 3.2). Histologically, primary tumors showed characteristic features of FH, consisting of a polymorphous population of bland spindle and histiocytoid cells with a mixed storiform and fascicular growth pattern and admixed foam cells, multinucleate cells and inflammatory cells. There were 9 cellular, 2 aneurysmal, 1 mixed atypical/cellular, 1 atypical and 1 epithelioid lesions. All tumors showed entrapment of hyalinized collagen bundles. Epidermal hyperplasia was present in most cases. Mitoses ranged from <1 to 13 per 10 HPF. Focal necrosis was seen in 3 primary tumors. Vascular invasion was not seen. Focal or multifocal SMA expression was seen in 5/7 cases and weak focal CD34 expression in 1/8. Tumor cells were negative for pan-keratin and S100. 9 tumors recurred locally, 5 as multiple "satellite" nodules. Time to first recurrence ranged from 6 weeks to 3 years. 1 patient had 3 local recurrences and 1 had 7. The local recurrences of 2 tumors showed increased cytologic atypia. Metastases occurred 0-96 months after diagnosis (mean 27.5) and involved the lungs (11 patients), soft tissues (6), lymph nodes (5) and liver (1). Metastases were morphologically similar to the primary tumors in all cases. 6 patients so far died of disease, with average time to death of 102 months (range 10-216). 2 patients are alive with stable disease 68 and 132 months after initial presentation and 65 and 66 months after lung metastases. 1 patient remains disease-free 7 years after resection of nodal and lung metastases. 1 patient died of unrelated disease 1 year after initial diagnosis.
Conclusions: Metastasis of morphologically benign cutaneous FH, although probably extremely rare, is a clinically aggressive event. Primary tumors tend to be large and cellular but aggressive behavior cannot be predicted on morphologic grounds. Early or frequent local recurrence may warrant close follow up.
Category: Dermatopathology

Monday, March 19, 2012 8:00 AM

Platform Session: Section F, Monday Morning


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