Clinicopathological characterization of
GLI1
‐altered mesenchymal neoplasms involving the dermis and subcutis: a series of eight cases
Joshua Del Papa, May Chan, Kyle Perry, Thomas Brenn, Katharina Wiedemeyer Aims
GLI1‐altered mesenchymal neoplasms are a recently described tumour group characterized by gene fusions or amplifications involving GLI1 . They show a wide anatomical distribution and harbour potential to metastasize. This study aims to add to the data on GLI1‐altered mesenchymal tumours involving the dermis and subcutis.
Methods
Departmental files were searched for GLI1‐altered mesenchymal neoplasms involving the dermis and/or subcutis. Clinicopathological features were reviewed, and cases were assessed by immunohistochemistry, GLI1 in situ hybridization, and targeted next‐generation sequencing.
Results
Eight tumours were identified and located on the scalp ( n = 3), gluteal region ( n = 2), inguinal region ( n = 1), supraclavicular area ( n = 1), and the left index finger ( n = 1). Seven men and one woman were affected (aged 24–78 years, median 53). Histopathologically, the tumours showed a multinodular growth pattern within the dermis and/or subcutaneous adipose tissue, were composed of ovoid cells with mild to moderate atypia, arranged in nests, sheets or strands. Most of them were associated with a rich capillary network. Mitotic activity was variable (0–22 per 10 high power fields). Necrosis was present in two cases. Gene fusion testing demonstrated a novel TUBA1A :: GLI1 fusion in one of three cases tested. This tumour showed strong SOX10 and S100 positivity by immunohistochemistry while the remaining tumours were negative or only focally positive for both markers. All patients were alive at last follow‐up: seven disease‐free without recurrences and one patient with advanced localized disease and metastasis to bone.
Conclusions
Superficial GLI1‐altered mesenchymal tumours show a spectrum of histopathological presentations, inconsistent immunophenotypes and variable biological behaviour.