Track: Clinical Studies

Abstract:

GLI1-altered mesenchymal neoplasms are a recently described tumor group characterized by gene fusions or amplifications involving GLI1. They show a wide anatomic distribution, affecting patients of a broad age range, and harbor potential to metastasize. The study aims to add to the data on cutaneous GLI1-altered mesenchymal tumors. Ethics approval was obtained, and H&E-stained sections and ancillary stains were reviewed. Six tumors were identified, located on the scalp (n=3), gluteal region (n=1), supraclavicular area (n=1), and the index finger (n=1). Five men and one woman were affected (aged 24–78 years, median 53). Histopathologically, the tumors were dermally based and composed of ovoid cells arranged in nests, sheets, and strands within a rich capillary network. Mitoses were infrequent, and necrosis was absent. Comprehensive fusion testing demonstrated a TUBA1A::GLI1 fusion in one of two tested cases. This tumor showed infiltrative growth, strong GLI1-in situ hybridization (GLI1-ISH) signals and SOX10 and S100 positivity. The remaining four tumors had weaker GLI1-ISH signals in comparison and were negative or focally/weakly positive for myoepithelial markers. CD56 was positive in all tested cases (2/2), while SMA and keratins showed focal patchy reactivity. In summary, cutaneous GLI1-altered mesenchymal tumors show a spectrum of histopathologic features and variable immunophenotypes.

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Kyle Perry