Comment
Our case of AFX is unique due to the patient’s atypical presentation of severe pain. Because AFX usually presents asymptomatically, pain is an uncommon symptom. Based on the histologic findings in our case, we suspected that neural involvement of the tumor most likely explained the intense pain that our patient experienced.
The presence of erosive pustular dermatosis of the scalp also is interesting in our case. This elderly man had an extensive history of actinic damage and had reported pustules, scaling, itching, and scabbing of the scalp. It is possible that erosive pustular dermatosis was superimposed over the tumor and could have been the reason that multiple biopsies were needed to eventually arrive at a diagnosis. The coexistence of the 2 entities suggests that the chronic actinic damage played a role in the etiology of both.
Classification
There is a question regarding nomenclature when discussing AFX. Atypical fibroxanthoma has been referred to as a variant of undifferentiated pleomorphic sarcoma, which is a type of soft tissue sarcoma. Atypical fibroxanthoma can be referred to as undifferentiated pleomorphic sarcoma if it is more than 2 cm in diameter, if it involves the fascia or subcutaneous tissue, or if there is evidence of necrosis.3 Atypical fibroxanthoma generally is confined to the head and neck region and usually is less than 2 cm in diameter. In this patient, the presentation was consistent with AFX, as there was evidence of necrosis and invasion into the subcutaneous fat. The fact that the lesion also appeared on the scalp further supported the diagnosis of AFX.
Pathology
Biopsy of AFX typically reveals a spindle cell proliferation that usually arises in the setting of profound actinic damage. The epidermis may or may not be ulcerated, and in most cases, it is seen in close proximity to the overlying epidermis but not arising from it.8 Classic AFX is composed of highly atypical histiocytelike (epithelioid) cells admixed with pleomorphic spindle cells and giant cells, all showing frequent mitoses including atypical ones.9 Several histologic subtypes of AFX have been described, including clear cell, granular cell, pigmented cell, chondroid, osteoid, osteoclastic, and the most common spindle cell subtype.9 Features that indicate potential aggressive behavior include infiltration into the subcutaneous tissue, vascular invasion, and presence of necrosis. A diagnosis of AFX is made by exclusion of other malignant neoplasms with similar morphology, namely spindle cell squamous cell carcinoma, spindle cell melanoma, and leiomyoscarcoma.9 As such, immunohistochemistry plays a critical role in distinguishing these lesions, as they arise as part of the differential diagnosis. A panel of immunohistochemical stains is helpful for diagnosis and commonly includes but is not limited to S-100, Melan-A, smooth muscle actin, desmin, and cytokeratin.
Sampling error is an inherent flaw in any biopsy specimen. The eventual diagnosis of AFX in our case supports the argument for multiple biopsies of an unknown lesion, seeing as the affected area was interpreted as both granulation tissue and AK prior to the eventual diagnosis. Repeat biopsies, especially if a lesion is nonhealing, often can help clinicians arrive at a definitive diagnosis.
Treatment
Different treatment options have been used to manage AFX. Mohs micrographic surgery is most often used because of its tissue-sparing potential, often giving the most cosmetically appealing result. Wide local excision is another surgical technique utilized, generally with fixed margins of at least 1 cm.10 Radiation at the tumor site is used as a treatment method but most often during cases of reoccurrence. Cryotherapy as well as electrodesiccation and curettage are possible treatment options but are not the standard of care.