Immunohistochemical expression of melanocytic and myofibroblastic markers and their molecular correlation in atypical fibroxanthomas and pleomorphic dermal sarcomas

Abstract

Background: Atypical fibroxanthomas (AFXs) and pleomorphic dermal sarcomas (PDSs) are UV-induced pleomorphic skin tumors with a non-specific immunoprofile. For that reason, exclusion of other dedifferentiated tumor entities by immunohistochemistry is still mandatory to avoid misdiagnosis.

Methods: We determined the expression frequency of several melanocytic and myofibroblastic markers investigating 50 AFXs and PDSs.. Next-generation-sequencing (NGS) was performed in microphthalmia-associated transcription factor (MiTF)-expressing cases.

Results: We identified one MiTF-expressing AFX and PDS, and two PDSs harboring single S100-positive dendritic cells whereas Melan A, HMB45, and SOX10 were negative. Calponin was moderately expressed by tumor giant cells in one PDS whereas h-caldesmon, desmin, and myogenin were not expressed in any of the AFXs or PDSs. The MiTF-positive AFX presented CDKN2A, OXA1L, and PDGFRA mutations whereas the PDS harbored a typical TP53 mutation. Both patients have not shown any tumor progression over the last 16 and 30 months.

Conclusion: Rarely, AFX and PDS express the melanocytic marker MiTF and/or the myofibroblastic marker calponin. In doubtful cases, using a panel of immunohistochemical markers helps to avoid misdiagnosis.

Keywords: MiTF; atypical fibroxanthoma (AFX); caldesmon; calponin; pleomorphic dermal sarcoma (PDS).