ATYPICAL FIBROXANTHOMA, CLEAR CELL OR FOAM CELL VARIANT
The clear cell or foam cell variant of atypical fibroxanthoma is uncommon. There is a widely held concept that atypical fibroxanthomas represent a peculiar cutaneous form of malignant fibrous histiocytoma that usually behaves in a benign fashion. If that be the case, then the clear cell or foam cell variant of atypical fibroxanthoma would be analogous to the so-called inflammatory or xanthomatous type of malignant fibrous histiocytoma.

Tumors of this type must be distinguished from balloon cell melanoma, sebaceous carcinoma, and clear cell carcinomas, primary or metastatic. Immunohistochemical studies, as were done in this case, are very helpful.

This particular tumor is S100 negative (marker for neural, neural crest or melanocytic differentiation), AE1/AE3 (cytokeratin) negative, and CD68 (a histiocyte marker) positive. The control sections and the internal control structures reacted unequivocally.


A rapidly growing mass from the forehead of an 84 year old female:
 
Scan power view. Note the bending (curving) of adnexal structures and/or acanthotic epidermis near the periphery the mass. This is indicative of an expansile lesion and often is associated with rapid growth.
Medium power view of the dermoepidermal junction. There was no evidence of the radial growth component of a melanoma peripheral to the tumor. Most of the atypical cells have clear or foamy cytoplasm. A few spindle cells are present, but most are epithelioid.
A medium power view that is representative of most of the interior of the tumor. This tumor is not as vascular as most metastatic renal cell carcinomas, but that might be a consideration in the absence of the immunohistochemical findings..
A high power view showing an abnormal mitosis (MIT). Other mitoses were easy to find.
A high power view from near the periphery of the tumor. Balloon cell melanoma and sebaceous carcinoma would be in the differential diagnosis.
 
Medium power view of the CD68 preparation. Epidermis is in the left side of the picture and it is nonreactive The tumor cells react strongly.
High power view of the tumor in the CD68 preparation.

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