Superficial <i>GLI1</i>‐amplified mesenchymal neoplasms: Expanding the spectrum of an emerging entity which reaches the realm of dermatopathology

Abstract

Mesenchymal neoplasms with GLI1 alterations (rearrangements and/or amplification) have been reported recently in several anatomic locations, which include head and neck, soft tissue, and gastrointestinal tract. Herein, to the best of our knowledge, we describe the first three cases of superficial/subcutaneous mesenchymal neoplasm with GLI1 amplification. The neoplasms exhibited low-grade cytologic features with predominant round cell morphology, glomangioma-like areas and a rich background capillary network. There were two to three mitotic figures per 10 HPF and focal necrosis in one case. The tumors exhibited variable expression of CDK4, MDM2, STAT6, D2-40, CD56 and cyclin D1. p16 had strong and diffuse nuclear and cytoplasmic expression in two cases. Numerous other stains were negative. Fluorescence in situ hybridization detected GLI1, DDIT3, and CDK4 coamplification in all cases, while next generation sequencing did not detect a GLI1 gene fusion. The overall features were compatible with a GLI1-amplified mesenchymal neoplasm. In Case 1 a new distant skin lesion appeared 1 month after the surgery exhibiting similar morphology albeit with a higher mitotic index. In Cases 2 and 3, there is no evidence of local recurrence or systemic disease after 8 years and 1 month of follow-up, respectively. These new cases of superficial GLI1-amplified neoplasm expand its clinical spectrum and enter the realm of dermatopathology. The combination of CDK4, cyclin D1, D2-40, and p16 expression with variable MDM2, STAT6, CD56, and S100 immunoreactivity in a low-grade neoplasm with round/ovoid cytomorphology resembling a vascular or adnexal neoplasm may suggest the possibility of GLI1-amplified neoplasm.