Abstract:

A 74-year-old man with a history of melanoma and non-melanoma skin cancers presented with a nodule on the scalp at a prior Mohs surgery site performed seven months ago for squamous cell carcinoma. Physical exam revealed an 8 mm soft purple nodule within a scar on the left parietal scalp. Punch biopsy demonstrated dermal pleomorphic spindled cells with prominent nucleoli and a moderate amount of cytoplasm with mitotic figures, areas of hemorrhage, and punctate necrosis. Immunohistochemistry was positive for CD10, focally positive for p63, and negative for AE1/AE3, CK-7, CK-20, MCK, p40, SOX10, S100, androgen receptor, desmin, CD34, pankeratin, CK-5/6, HMB45, Mart1, SMA, and ERG. After consultation with surgical pathology, the consensus opinion was of a cutaneous spindled malignancy most representative of the spectrum of atypical fibroxanthoma/pleomorphic dermal sarcoma (AFX/PDS). Next generation sequencing revealed a mutational profile consistent with the molecular signature of AFX/PDS with mutations in CDKN2A, NOTCH1/2, TP53, and FAT1. A multidisciplinary cutaneous oncology committee recommended Mohs surgery, and the lesion was excised with clear margins. AFX/PDS are fibrohistiocytic tumors that lie on a clinicopathologic spectrum with AFX being more superficial with minimal metastatic potential and PDS having greater subcutaneous invasion, tumor necrosis, or high-grade histological features. As illustrated in our case, they most commonly affect older males with sun-damaged skin, particularly favoring the scalp. AFX/PDS is a diagnosis of exclusion using immunohistostaining with further substantiation using next-generation sequencing. Differentiating PDS from AFX is critical given the higher risk for metastasis and recurrence of PDS. The treatment of choice is complete surgical excision. Our case highlights the first report, to our knowledge, of the development of AFX/PDS arising within a site of non-melanoma skin cancer that was recently treated with Mohs surgery.

Financial Disclosure:
No current or relevant financial relationships exist.

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Jennifer Laborada, BS