Abstract

Atypical fibroxanthoma(AFX) and pleomorphic dermal sarcoma(PDS) are unusual dermal mesenchymal tumors of uncertain histogenesis. They typically arise on sun-damaged skin in elderly males. AFX and PDS show overlapping histologic, immunophenotypic and molecular features. Typical tumor histology shows a mixture of markedly atypical spindled and epithelioid cells with admixed giant cells and numerous atypical mitoses. Immunohistochemically(IHC), they are negative for keratins, melanocyte markers, vascular markers, and smooth muscle markers (variable expression of SMA). Histopathologic differentiation is based on deeper subcutaneous involvement, perineural invasion, lymphovascular invasion or necrosis being present in PDS. PDS shows higher rates of local recurrence and metastasis, so differentiating between the two is clinically relevant. Besides the typical histologic appearance, variant morphologies have been reported, including clear cell and spindle cell variants. Here, we present three cases with similar clinical presentation of a rapidly growing ulcerated nodule in elderly men, that demonstrate the histologic variability of AFX/PDS. The first case shows the characteristic appearance of AFX as previously described. Unlike most AFX/PDS which typically occur on the scalp, this case arose on the forearm. In the second case, the scalp tumor shows epithelioid to spindled cells with highly vacuolated clear cytoplasm, compatible with clear cell variant of AFX/PDS given the supporting IHC findings. The third case shows a scalp tumor composed of markedly atypical and pleomorphic spindle cells with IHC findings and lymphovascular invasion supporting an interpretation of PDS.