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Collision of Atypical Fibroxanthoma and Acantholytic Squamous Cell Carcinoma In Situ

Hyatt, Ann-Marie MD; Mutasim, Diya F. MD; Spicknall, Kerith E. MD

The American Journal of Dermatopathology: July 2012 - Volume 34 - Issue 5 - p 563–564
doi: 10.1097/DAD.0b013e31822e63c8
Letters to the Editor

Department of Dermatology University of Cincinnati College of Medicine Cincinnati, OH

The authors have no funding or conflicts of interest to declare.

To the Editor:

A previous case of atypical fibroxanthoma (AFX) surrounding a trichilemmal cyst with squamous cell carcinoma in situ (SCCis) arising within its wall has been reported.1 We report a collision tumor of SCCis occurring in the epidermis overlying an AFX.

A 60-year-old white male presented with a several year history of a tender lesion on the left cheek. Clinical examination revealed a 7-mm firm pink papule on his left preauricular cheek. He had no palpable lymphadenopathy. Shave biopsy revealed full-thickness atypia and acantholysis of keratinocytes. Within the papillary dermis, unconnected to the overlying atypical epidermis, was a proliferation of plump spindle and epithelioid cells with marked pleomorphism, multinucleation, vesicular nuclei, markedly abundant cytoplasm, and bizarre mitotic figures (Fig. 1). Antibodies to pan-keratin (AE1/AE3) and high molecular weight keratin (HMWK; 34betaE12) labeled atypical epidermal cells, characteristic of SCCis, but did not label the pleomorphic dermal cells (Fig. 2A). In contrast, the pleomorphic dermal cells were strongly and diffusely labeled by antibodies to CD10 (Fig. 2B) but not by antibodies to pankeratin or HMWK, characteristic of AFX. Thus, the histopathologic and immunohistochemical findings were characteristic of a collision tumor of acantholytic SCCis and AFX.





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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