Parotid Gland Solitary Fibrous Tumor: A Case Report and Clinicopathologic Review of 22 Cases from the Literature

Solitary fibrous tumors (SFTs) are rare tumors in the head and neck, and even more so in the parotid gland. The mass-like clinical presentation and histologic features result in frequent misclassification, resulting in inappropriate clinical management. There are only a few reported cases in the English literature. Twenty-one patients with parotid gland solitary fibrous tumor were compiled from the English literature (Medline 1960–2011) and integrated with this case report. The patients included 11 males and 11 females, aged 11–79 years (mean, 51.2 years), who presented with a parotid gland painless mass gradually increasing in size or with compression symptoms, with a mean duration of symptoms of 24.7 months. The mean tumor size was 4.5 cm. Grossly, all tumors were described as well-circumscribed to encapsulated, firm, homogenous white to tan masses. Seven patients had a preoperative fine needle aspiration performed, with the majority interpreted to represent pleomorphic adenoma or cementifying fibroma. Histologically, the tumors were well circumscribed, although many tumors showed focally entrapped normal salivary gland acini and ducts at the edge. The tumors were cellular, arranged in haphazard short interlacing fascicles of spindled to epithelioid cells. The spindled cells showed tapering cytoplasm with monotonous, round to oval nuclei with coarse nuclear chromatin distribution. Keloid-like to wiry collagen was present between the neoplastic cells. Mitoses were identified in most cases, while necrosis was absent. Isolated, patulous vessels were present, but a well developed “hemangiopericytoma-like” vascular pattern was not seen. Three tumors were classified as malignant, showing marked nuclear pleomorphism and increased mitoses. When immunohistochemistry was performed, all tumors showed strong and diffuse vimentin, with a majority showing CD34, bcl-2 and CD99 immunoreactivity; all cases tested were negative for S100 protein, cytokeratin, EMA, CAM5.2, smooth muscle actin, muscle specific actin, desmin, MYOD1, myogenin, CD117, GFAP, CD31, FVIII-RAg, collagen IV, p63, p53, calponin, caldesmon, CD56, NFP, and ALK-1. The principle differential diagnoses include pleomorphic adenoma, myoepithelioma, nodular fasciitis, schwannoma, fibromatosis coli, spindle cell “sarcomatoid” carcinoma, and spindle cell melanoma. All patients were managed with surgery, while two patients also received radiation therapy. Metastatic disease was identified in one patient immediately after excision. All patients with follow-up were alive without evidence of disease (n = 18), but the average follow-up is only 1.9 years. One patient is alive with disease at 12 months. Parotid gland SFT is a rare tumor, usually presenting in middle aged adults as a slowly growing mass. Characteristic histologic appearance with CD34 and bcl-2 immunoreactivity support the diagnosis. Surgery is the treatment of choice to yield a good outcome.