OBJECTIVETo study the clinicopathologic characteristics of atypical fibrous histiocytoma (AFH), with emphasis on differential diagnosis.

METHODSThe clinical and pathologic features were reviewed in 24 cases of AFH (from 2007 to 2012). The follow-up data were analyzed. Immunohistochemical study using EnVision method was carried out.

RESULTSThere were 10 males and 14 females with age at presentation ranging from 8 to 67 years (mean = 41 years and median = 39 years). The tumor occurred in the extremities (number = 14), trunk (number = 8) or head and neck region (number = 2). Apart from one case, all were located in the dermis. The clinical appearance was similar to those of classic fibrous histiocytoma. Histologically, the tumor was characterized by various number of hyperchromatic bizarre cells scattered in the background. Mitotic figures including atypical ones were noted, especially in the more cellular areas. Immunohistochemical study showed that the tumor cells expressed vimentin. Focal positivity for alpha-smooth muscle actin was demonstrated in some cases. Follow-up information was available in 14 cases. Three of them suffered local recurrence. None of these cases had distant metastasis.

CONCLUSIONSAtypical fibrous histiocytoma represents a pleomorphic variant of fibrous histiocytoma. Although the tumor exhibits worrisome features, it usually pursuits a relatively benign course. Nevertheless, rare cases may recur, especially after incomplete excision. AFH is sometimes mistaken as atypical fibroxanthoma. A distinction between the two entities is warranted as they represent two different entities.