Abstract:

Myofibroblastoma (MF) is a rare, benign mesenchymal tumor first described as a distinctive neoplasm of the breast. Extra-mammary myofibroblastoma (EMMF) is a histologically and genetically identical lesion occurring outside the breast whose prevalence has become increasingly recognized. EMMF occurs most often in the inguinal region but has been reported in a variety of anatomic locations. Only four cases in the head and neck have been described in the English literature. Herein is presented the first case of EMMF arising in the oral cavity. A 59-year-old woman presented with a six-month history of an asymptomatic nodule in the oral cavity. Physical examination revealed a 1.5 cm nodule on the buccal surface of the lower lip. Wide local excision was performed. Histopathologic examination revealed variably sized, haphazard fascicles of monomorphic spindle cells with hyalinized collagen bundles and absent fat. The spindled cells were diffusely positive for CD34, and focally positive for progesterone receptor. Desmin, SMA, androgen receptor, estrogen receptor, S100, and STAT6 were negative. Rb1 expression was lost in tumor cells. Thus, the diagnosis of EMMF was made. The chief differential diagnoses include spindle-cell lipoma (SCL) and angiofibroma (CA). Along with EMMF, these tumors are members of the 13q14 deletion/RB1 loss family. Their distinction from one another may be purely academic, as all three are similarly benign. Indolent but locally aggressive (solitary fibrous tumor, desmoid fibromatosis) and frankly malignant (low grade peripheral nerve sheath tumor, dermatofibrosarcoma protuberans) entities can be excluded by immunohistochemistry and careful microscopic examination. Extensive sampling of EMMF is important to search for atypia, mitoses, and necrosis, thus excluding the possibility of malignancy. Clinicians and pathologists alike should be aware of this entity and its potential to arise rarely in unusual locations, such as the oral cavity lesion reported herein, to ensure the correct diagnosis is made.

Financial Disclosure:
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