AFX is a superficial fibrohistiocytic tumor that presents on the head and neck of elderly patients and is usually a pink or red, solitary, firm, asymptomatic papule or nodule.2,3 Histologically, AFX reveals a dermal proliferation of spindle and epithelioid cells with (often marked) pleomorphism, bizarre mitotic figures, and multinucleated cells.3 There are many variants of AFX, including spindle cell nonpleomorphic, clear cell, osteoclastic, and granular cell.3 Cutaneous squamous cell carcinoma (SCC) has a very diverse range of clinical and pathological subtypes including, but not limited to, acantholytic poorly differentiated and spindle cell.4
A patient with a forehead lesion containing both an SCCis arising within the wall of a trichilemmal cyst and surrounding AFX has been previously reported.1 AFX and SCC occurring together on the conjunctiva5 and face6 of patients with xeroderma pigmentosum have also been reported. It is not surprising to observe a collision of SCCis (or SCC) and AFX because both tumors occur in photoexposed skin.7 In the present case, full thickness epidermal atypia was observed immediately overlying undifferentiated pleomorphic dermal cells, making it necessary to exclude invasive poorly differentiated SCC arising from SCCis by staining with antibodies to pankeratin. Furthermore, because keratinocytes in spindle8 and poorly differentiated7 SCC may lose expression of low molecular weight keratin, we used antibodies to HMWK (34BetaE12) to exclude poorly differentiated SCC. Finally, strong and diffuse labeling of pleomorphic dermal cells with antibodies to CD10 confirmed the diagnosis of AFX.9
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