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A Difficult Diagnosis

What is the ulcerated pink nodule on this patient's scalp?

Coerdt, Kathleen M.; Khachemoune, Amor MD

Author Information
Journal of the American Academy of Physician Assistants: August 2020 - Volume 33 - Issue 8 - p 55-56
doi: 10.1097/01.JAA.0000684144.71148.80
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A 79-year-old man presented to the dermatology clinic with a 5-month history of a nodule on the frontoparietal scalp.


The patient first noted the lesion when he nicked it while shaving 5 months ago. The lesion was slowly growing in size and bled frequently. He reported no associated pain in the affected area and denied fever, chills, weight loss, or malaise. He had no personal history of skin cancer.

Physical examination

The lesion was a 1.5- to 2-cm, pink, round nodule with overlying hemorrhagic crust near the vertex of the scalp (Figure 1). No such nodules were appreciated on the neck, extremities, or trunk. No other lesions were observed on the scalp. The remainder of the physical examination was unremarkable.

The nodule with overlying hemorrhagic crust on the vertex of the patient's scalp


  • basal cell carcinoma (BCC)
  • squamous cell carcinoma (SCC)
  • malignant melanoma
  • atypical fibroxanthoma


An excisional biopsy was done to visualize the base of the lesion, and the lesion demonstrated histologic features of an atypical fibroxanthoma. Histopathologic analysis showed pleomorphic and hyperchromatic spindle cells with numerous atypical mitoses, admixed foamy histiocytes, and multinucleated giant cells. Immunohistochemical stains were intensely positive for CD68, moderately positive for S-100 in nerve endings, and mildly positive for Ki67, confirming the histologic diagnosis of atypical fibroxanthoma. Stains were negative for cytokeratin, alpha-smooth muscle actin (SMA), and melan-A.

Nodular BCC usually presents as a pearly papule or nodule with rolled borders and telangiectasias. SCC usually presents as a firm scaly nodule. Both BCC and SCC stain positively for cytokeratin. Leiomyosarcoma is a rare smooth muscle tumor that clinically presents as a firm dermal nodule. It stains positively with SMA. Melanoma often presents as a pigmented macule or nodule. The negative melanin-A stain helped rule out this diagnosis.

The tumor was treated using Mohs micrographic surgery. Complete clearance was achieved following one stage.


Atypical fibroxanthoma is a rare, dermal mesenchymal neoplasm.1 Usually it is found in older adults, often in their 60s and 70s.2-4 Atypical fibroxanthoma has a predilection for white men, though any ethnicity can be affected.1 Some risk factors are ultraviolet radiation, fair skin, xeroderma pigmentosum, immunosuppression, and a past personal history of SCC or BCC.2,4

Atypical fibroxanthoma presents clinically as a solitary, red-to-pink, dome-shaped or solid nodule.4 The nodule grows rapidly over several months, rarely exceeding 2 cm in size.1 The lesion can ulcerate, leading to a hemorrhagic crust.1,4 Atypical fibroxanthoma most commonly is found on sun-damaged skin of the head and neck.1 It is rarely found on the extremities or trunk.

Histologic evaluation is necessary for diagnosis because the neoplasms on the differential can present similarly. Once spindle cells are appreciated on histology, spindle-cell SCC, leiomyosarcoma, desmoplastic malignant melanoma, and atypical fibroxanthoma must be considered. Atypical fibroxanthoma is a diagnosis of exclusion. The lesion appears as a well-circumscribed tumor in the dermis. Peripheral collaret formation often occurs in the surrounding hyperplastic epidermis.4 Enlarged, pleomorphic spindle cells, epithelioid cells, histiocyte-like cells, and atypical multinucleated giant cells may be appreciated.1 The cells have hyperchromatic nuclei with numerous atypical mitoses.1

Histology alone is not enough for diagnosis; immunohistochemistry is essential. No one specific marker for atypical fibroxanthoma exists, so a panel of antibodies must be ordered to distinguish it from other neoplasms.1 Atypical fibroxanthoma is positive for CD68, CD10, vimentin, p53, and calponin, and negative for cytokeratin, p63, S-100, CD34, ERG, desmin, and h-caldesmon.1,4 Atypical fibroxanthoma has variable positivity for SMA, procollagen-1, melan-A, and HMB45.1 The lesion in the case above was strongly positive for CD68, in line with atypical fibroxanthoma. The lesion had some S-100 positivity in the nerve endings, which is more typical of malignant melanoma. Dendritic cells in an atypical fibroxanthoma, however, may express S-100 positivity, skewing the typical immunohistochemistry results.5 The negative melan-A stain placed malignant melanoma lower on the differential. The negative cytokeratin stain helped rule out spindle-cell SCC. Overall, the histologic picture, the CD68 positivity, and the cytokeratin negativity confirmed the atypical fibroxanthoma diagnosis.

Atypical fibroxanthoma typically is benign with a favorable prognosis.1 Recurrence and metastasis are rare but possible.1-3 Complete excision of the neoplasm is the gold standard for treatment due to the lesion's metastatic potential.1,6 Including the base of the lesion on initial biopsy is crucial to rule out undifferentiated pleomorphic sarcoma, which some consider to be a deep version of atypical fibroxanthoma, though this remains controversial.5 Undifferentiated pleomorphic sarcoma is more aggressive than atypical fibroxanthoma and has a higher risk of metastasis.5 Two techniques are used for excision—Mohs surgery and wide local excision.4,6 Mohs surgery often is preferred because it has a higher cure rate with more tissue preservation.3 Tissue sparing is especially important in cosmetically sensitive areas, such as the face. Because atypical fibroxanthoma primarily is found on the head and neck, Mohs surgery is the preferred treatment.2 Wide local excision is more widely available than Mohs surgery, so it is often used to treat atypical fibroxanthoma.6 When performing wide local excision, clinicians should ensure a clean margin of 2 cm, though no specific guidelines about atypical fibroxanthoma margins have been published.3,4,7 Likewise, no specific guidelines for follow-up have been published, although most clinicians recommend follow-up every 6 months to evaluate for recurrence or new skin malignancies.


When evaluating a patient's skin lesion, clinicians who work in primary care or dermatology should consider the lesion's location, morphology, histology, and immunohistochemistry in order to make a diagnosis. Consider atypical fibroxanthoma in older adults with ulcerated, pink-to-red, solitary papules or nodules on the head or neck. Histologic evaluation shows pleomorphic spindle cells, epithelioid cells, multinucleated giant cells, and numerous atypical mitoses. Immunohistochemistry is typically positive for CD68, vimentin, and p53 and negative for cytokeratin, S-100, and CD34. Distinguishing atypical fibroxanthoma from spindle-cell SCC, BCC, and malignant melanoma is key because these neoplasms can present similarly.


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