Morphological and immunohistochemical characteristics of atypical fibroxanthoma with a special emphasis on potential diagnostic pitfalls: a review.
The present manuscript gives emphasis on recognizing different morphological variants of atypical fibroxanthoma (AFX), on validation of immunohistochemical markers and on discussing potential diagnostic pitfalls.


METHODS
Histological features analyzed in 66 AFXs were: ulceration, morphological variants, growth pattern, location in the skin and vascular/perineural invasion. The antibodies used were CK-MNF116, CK-AE1/AE3, S100, smooth muscle actin, desmin, CD31 and EMA.


RESULTS
The study included 59 males, 7 females, aged 55-95 years, mean 77 years. All developed on sun damaged skin. Ulceration was present in 50%. Morphological patterns were pleomorphic spindle and epithelioid cells (60.6%), predominantly spindle cells (19.7%), purely spindle-cells (13.6%), and predominantly epithelioid cells (6.1%). Most were localized in the dermis (57.6%). An expansile (36.4%) rather than infiltrative (6.1%) growth into superficial subcutis was also noted. No vascular/perineural invasion was seen. Additional changes were hemorrhagic and pseudoangiomatous areas (24.2%), granular cell change (22.7%), keloid-like areas (9.1%), myxoid change (7.6%), osteoclast-like giant cells (6.1%) and clear cell change (4.6%). AFXs were consistently negative for S100, CK-MNF116, CK-AE1/AE3 and desmin. Focal positivity for SMA (45.2%), EMA (24.4%) and CD 31 (9.5%) was seen.


CONCLUSIONS
A diagnosis of AFX is still made by exclusion of other malignant neoplasms with similar morphology. Immunohistochemistry plays a crucial role in this distinction, but can also be misleading. This study expands the spectrum of non-vascular CD31 positive tumors.
Luzar
Bostjan
B
Institute of Pathology, Medical Faculty University of Ljubljana, Korytkova 2,1000 Ljubljana, Slovenia.
Calonje
Eduardo
E
D000368:Aged; D000369:Aged, 80 and over; D001132:Arm / Q000473:pathology; D014408:Biomarkers, Tumor; D003937:Diagnosis, Differential; D005260:Female; D005355:Fibrosis / Q000473:pathology; D006258:Head and Neck Neoplasms / Q000473:pathology*; D018219:Histiocytoma, Benign Fibrous / Q000473:pathology*; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D008875:Middle Aged; D012535:Scalp / Q000473:pathology; D012737:Sex Factors; D012878:Skin Neoplasms / Q000473:pathology*; D014973:Xanthomatosis / Q000473:pathology*
D014408:Biomarkers, Tumor