GLI1-altered mesenchymal tumors of the head and neck.

GLI1-altered mesenchymal tumors are a group of soft tissue tumors that have emerged as a new entity, in large part, as a result of increased next-generation sequencing (NGS)-based DNA and RNA sequencing of tumors. Over the last decade, multiple case reports and small series have reported such tumors involving multiple sites (including soft tissue, head and neck and viscera). They appear to have rather distinctive morphology and can either show GLI1-gene fusions or GLI1-gene amplifications. Although cases with metastasis are increasingly recognized, definite morphologic indicators of metastasis have not yet been identified. In this review, we focus on GLI1-altered mesenchymal tumors of the head and neck, with an emphasis on clinicopathologic features, molecular findings and approach to the diagnosis.