Sclerosing Epithelioid Fibrosarcoma of the Jaw: Late Recurrence from a Low Grade Fibromyxoid Sarcoma.

Sclerosing epithelioid fibrosarcoma (SEF) is an uncommon variant of fibrosarcoma that is characterized by a distinct morphology. It most frequently presents in the deep soft tissues of the lower extremities, often in intimate association with fascia and periosteum, although reports of the head and neck involvement have been reported. A minority of cases show morphological, immunohistochemical and molecular overlap with low grade fibromyxoid sarcoma (LG-FMS). Herein, we describe a case of a bland spindle cell neoplasm presenting in the jaw that was initially incompletely excised. Over the course of 20 years the tumor subsequently recurred with a SEF morphology. Molecular testing performed on both specimens subsequently confirmed the presence of an EWSR1-CREB3L1 gene fusion. This report highlights the diagnostic difficulty with LG-FMS, particularly in unusual anatomic locations; reiterates the potential for the uncommon EWSR1-CREB3L1 fusion product in LG-FMS; and, reaffirms the potential for progression and/or overlap between LG-FMS to SEF over time.