Atypical fibroxanthoma (AFX) is a low-grade dermal malignancy comprised of atypical spindle cells.1 Classified as a superficial fibrohistiocytic tumor with intermediate malignant potential, AFX has an incidence of approximately 0.24% worldwide.2 The tumor appears mainly on the head and neck in sun-exposed areas but can occur less frequently on the trunk and limbs in non–sun-exposed areas. There is a 70% to 80% predominance in men aged 69 to 77 years, with lesions primarily occurring in sun-exposed areas of the head and neck.3 A median period of 4 months between time of onset and time of diagnosis has been previously established.4
When AFX does occur in non–sun-exposed areas, it tends to be in a younger patient population. Clinically, it presents as a rather nondescript, firm, erythematous papule or nodule less than 2 cm in diameter. Atypical fibroxanthoma most often presents asymptomatically, but the tumor may ulcerate and bleed, though pain and pruritus are uncommon.5 Findings are nonspecific, and the diagnosis must be confirmed with biopsy, as it can resemble other common dermatological lesions. The pathogenesis of AFX has been controversial. Two different studies looked at AFX using electron microscopy and concluded that the tumor most closely resembled a myofibroblast,6,7 which is consistent with current thinking today.
Atypical fibroxanthoma is believed to be associated with p53 mutation and is closely linked with exposure to UV radiation due to its predominance in sun-exposed areas. Other predisposing factors may include prior exposure to UV radiation, history of organ transplantation, immunosuppression, advanced age in men, and xeroderma pigmentosum. The differential diagnosis for AFX encompasses basal cell carcinoma, squamous cell carcinoma, Merkel cell carcinoma, adnexal tumor, and pyogenic granuloma.
A 93-year-old man was referred to our clinic for treatment of erosive pustular dermatosis of the scalp with photodynamic therapy (PDT). He had a more than 20-year history of multiple skin lesions including basal cell carcinoma, squamous cell carcinoma, and actinic keratoses (AKs). For one year prior to the current presentation the patient had concerns of pustules, scaling, itching, and scabbing on the scalp. The patient admitted that the pruritus caused him to pick at the scabs on the scalp. He had previously been treated with lactic acid 12% neutralized with ammonium hydroxide, tacrolimus, and halobetasol, all to no avail.
On physical examination, the lesions appeared erosive with crusting and granulation tissue (Figure 1A). The presentation was consistent with erosive pustular dermatosis of the scalp. Biopsy revealed granulation tissue. The patient underwent PDT and prednisone treatment with improvement. Additional biopsies revealed AKs. His condition improved with 2 PDT sessions but never fully cleared. During the PDT sessions, the patient reported intense unilateral headaches without visual changes. The headaches were intermittent and not apparently related to the treatments. He was referred for a temporal artery biopsy and rebiopsy of the remaining lesion on the scalp. The temporal artery biopsy was negative. The lesion that remained was a large nodule on the vertex scalp, and biopsy revealed AFX.
Immunohistochemical marker studies for S-100 and cytokeratin were negative. Invasion into subcutaneous fat was encountered (Figure 2A). Highly atypical spindle cells and mitoses were present (Figure 2B). Neoplastic cells were noted adjacent to nerve (Figure 2C). Excision of the lesion was curative, and his symptoms of pain and erosive pustular dermatosis resolved weeks thereafter (Figure 1B). The area of erosive pustular dermatosis was not excised, but symptoms resolved weeks following excision of the AFX.