Spindle cell mesenchymal tumours of the head and neck: emerging and recently described entities characterised by molecular findings

The classification of mesenchymal neoplasms is rapidly expanding, with a marked increase in entities defined not only by traditional morphological parameters, but according to the underlying molecular genetic alterations driving tumorigenesis. We aim to provide an overview of a selection of recently described and emerging entities relevant to the head and neck pathologist, with an emphasis on the morphological and immunohistochemical findings that can prompt consideration of referral for molecular testing. In this review we provide an overview of: 1) TIMP3::ALK rearranged tumour, 2) spindle cell/sclerosing rhabdomyosarcoma with emphasis on tumours harbouring rearrangements of TFCP2, 3) EWSR1::POU2AF3 sarcoma, 4) sarcomas with EWSR1::PATZ1 fusions and 5) GLI1-altered soft tissue tumour.