D. Solitary fibrous tumor
Solitary fibrous tumors (SFTs) are rare, spindle-cell neoplasms of mesenchymal origin that preferentially arise in serosal membranes, intracranial and spinal cord meninges, and the extremities.1 While pleural SFTs are most common, an estimated 6% to 18% of SFTs occur in the head and neck region, most frequently involving the oral cavity, sinonasal tract, orbit, or salivary glands.2 Peak incidence is in middle-aged adults (median age, 51 years); there is no sex predilection. Patients most commonly present with a small (<5 cm), painless, slow-growing mass, with or without site-related compressive symptoms. Standard of care is wide surgical resection; however, rates of positive surgical margins are high, and postoperative radiation therapy may be considered.2 Under the 2020 World Health Organization Classification of Soft Tissue and Bone Tumors, SFTs are categorized as fibroblastic/myofibroblastic neoplasms with intermediate—rarely metastasizing—biological behavior, and multiple case series have described the indolent nature of SFT.1- 3 However, the clinical behavior of individual tumors is notoriously difficult to predict: there is a predilection for late local recurrence in 5% to 40% of patients,1 with varying reports of median time to recurrence between 37 and 120 months.1 Several risk-assessment schema have been proposed to predict the behavior of SFT (ie, risk of metastasis, risk of recurrence, disease-free and overall survival).1,4 These schema consider factors such as patient age, tumor size, depth of location, cellularity, pleomorphism, and mitotic rate/index to stratify SFTs as very low, low, moderate/intermediate, or high risk.1,4