Myxoid atypical fibroxanthoma: a previously undescribed variant

Atypical fibroxanthomas (AFX) are dermal-based cutaneous tumors typically found in sun-damaged skin of the elderly. Histologic variants include spindle cell, clear cell, osteoid, osteoclastic, chondroid, pigmented, and granular cell. To date, myxoid change in AFX, has not been described.

Four cases were retrieved from the consultation and surgical pathology files of Knoxville Dermatopathology Laboratory, Knoxville, Tennessee during a 4-year period. The clinical and histologic findings were reviewed and Alcian blue/periodic acid-Schiff (PAS) stain and panel of immunohistochemical stains was obtained.

All 4 lesions occurred as solitary lesions in elderly males on the head and neck (2 cases) and upper extremity (2 cases). Histologically all tumors demonstrated a well-circumscribed, cellular lesion centered in the dermis and composed of a mix of atypical pleomorphic and spindle cells in a prominent myxomatous background. A junctional component was absent and the tumors did not arise from the epidermis or adnexal structures. Subcutaneous involvement was absent in all cases. Tumor cells were negative for melanocytic and epithelial markers. Positive staining was noted with CD10 (3/4 cases) and vimentin (4/4 cases).

Myxoid change in AFX is rare and previously undescribed in the English literature. Myxoid change may be a prominent finding in benign and malignant cutaneous tumors and awareness of this variant of AFX will avoid misdiagnosis.