Solitary Fibrous Tumor of the Hard Palate: A Case Report and Review of the Literature

Solitary fibrous tumors (SFTs) are a relatively rare group of mesenchymal neoplasms. Klemperer and Rabin first described a case in the pleura in 1931, but SFTs have also been reported in extrapleural sites, including the oral cavity. SFTs of the oral cavity most commonly affect the buccal mucosa and tongue of female patients in their sixth decade of life. To date, only seven cases of oral SFTs located in the palate (three soft palate, four hard palate) have been documented in the literature. We present a case of a solitary fibrous tumor of the hard palate with review of the literature.

A 26-year-old female with a past medical history significant for tuberous sclerosis presented to NYU College of Dentistry reporting a several year history of a painless mass of the hard palate. The mass was biopsied, initially diagnosed as cellular angiofibroma, and referred to the Department of Oral & Maxillofacial Surgery at Bellevue Hospital Center for further management. Examination revealed a 3x3cm exophytic lesion on the right hard palate extending past the midline. The mass was non-tender to palpation and the mucosa overlying the lesion was intact without evidence of ulceration or necrosis. A CTA of the lesion showed mild prominence of vasculature along the right lateral soft and hard palate, possibly demonstrating supply from the ascending palatine artery. Postoperative surgical histopathology demonstrated a well-circumscribed, non-encapsulated lesion composed of spindle cells with admixed background slit-and-staghorn vessels in a patternless pattern. Immunohistochemical staining was diffusely positive for CD34 and Bcl-2 while negative for SMA, CD31, AE1/AE3, CAM5.2, S-100, EMA and demonstrated low KI-67 immunolabeling.

SFTs constitute a heterogeneous group of rare spindle-cell tumors that include benign and malignant neoplasms. Their cell of origin remains uncertain since CD34-positive spindle cells are also found in other mesenchymal neoplasms, such as giant cell angiofibromas and hemangiopericytoma, and share similar microscopic, immunohistochemical and biologic features.

SFTs are usually well-demarcated and partially encapsulated neoplasms. Microscopically, SFTs show a wide range of morphological characteristics from predominantly fibrous lesions containing alternating fibrous areas and hyalinized thick-walled vessels to more cellular fibrous neoplasms with a “patternless pattern” and thin-walled branching vessels. Immunohistochemically, SFTs usually demonstrate CD34 and CD99, and vimentin positivity with variable Bcl-2, EMA and SMA positivity and are usually negative for CD68, desmin, pan-cytokeratins, and S-100 protein immunoreactivity. Malignant SFTs tend to demonstrate nuclear atypia, hypercellularity, loss of margin integrity, high mitotic rate (>4 per 10 high power fields) and lose CD34 immunoreactivity while overexpressing S-100 and p53. Our patient’s lesion demonstrated positivity for only CD34 and Bcl-2, which, along with its aforementioned histological characteristics, was more consistent with the diagnosis of benign SFT than for the original diagnosis of cellular angiofibroma. CT imaging typically demonstrates SFTs as well-circumscribed, hypervascular masses with varying degrees of enhancement, necrosis or cystic change, and may show occasional internal calcification. Our patient's lesion demonstrated mild prominence of vasculature associated with the lesion with no invasion into the adjacent hard palate, consistent with a benign tumor.

Due to its rare entity, SFTs are seldom considered in the differential diagnosis for submucosal masses of the oral cavity. However, reports suggest that SFTs may possess malignant characteristics and, thus, should be considered when evaluating well-circumscribed, solid masses in the oral cavity.

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