Pseudolymphomatous Atypical Fibroxanthoma

Abstract

Atypical fibroxanthoma is a rare mesenchymal skin tumor of intermediate malignancy that typically occurs on sun-damaged skin of elderly patients. Histologically, it is composed of pleomorphic cells with hyperchromatic nuclei and abundant cytoplasm, commonly arranged in a spindle cell pattern. Different histologic variants have been described during the past years. We present a case of atypical fibroxanthoma containing a dense inflammatory infiltrate, which in conjunction with the existence of immunoblast-like and Reed-Sternberg-like neoplastic cells could be misinterpreted as a lymphoid neoplasm. Immunohistochemical studies revealed strong positivity of tumor cells for CD10 and negativity for cytokeratins, p63, p40, S100, SOX10, ERG, actin, desmin, B and T-cell markers, BCL6, CD15, and CD30. The inflammatory infiltrate contained a mixed reactive T- and B-cell population with negative T-cell receptor and immunoglobulin heavy rearrangements. We discuss the differential diagnosis of this entity in which clinical, immunohistochemical, and molecular features are essential to avoid the diagnosis of a lymphoproliferative disease.

Spindle-cell (Sarcomatoid) Variant of Cutaneous Anaplastic Large-cell Lymphoma (C-ALCL)

“…AFX of the skin sometimes can be accompanied by a rich lymphocytic infiltrate, and in some circumstances abundant CD30 + cells are present. 31,32 As opposed to C-ALCL, CD45 is negative in the tumor cells. In addition, a substantial degree of cellular pleomorphism is typical of AFX, and prominent superficial actinic damage (in highly sun-exposed areas) is the rule for such tumors.…”

“…These tumors show a prominent epidermal collarette, lack significant pleomorphism, contain rare mucinous cells, and are CD45 negative. AFX of the skin sometimes can be accompanied by a rich lymphocytic infiltrate, and in some circumstances abundant CD30 + cells are present 31,32. As opposed to C-ALCL, CD45 is negative in the tumor cells.…”