Ossifying fibromyxoid tumour (of soft parts) of the head and neck: a clinicopathological and immunohistochemical study of nine cases.

Ossifying fibromyxoid tumour (OFT) is a recently described, mesenchymal neoplasm originally defined as a borderline or low-grade malignant lesion. Prior reports of OFT characterize it as a slow growing lesion with a propensity to occur in both the upper and lower extremities. Most OFTs have occurred within the deep subcutis or skeletal muscle. We report nine cases which arose in the head and neck region. Six of the nine tumours were classified as ossifying variants of OFT while two were non-ossifying variants that lacked a discernable shell of lamellar bone. One tumour was classified as a malignant OFT. Seven lesions occurred in a subcutaneous site while two lesions occurred intraorally beneath the gingival and palatal mucosa. The OFTs occurred in six men and three women (age range of 29-75 years). The tumours had histological features compatible with previously described OFTs and consisted of lobulated nests of small, cytologically bland round cells (with the exception of one malignant OFT), with a myxoid to hyalinized stroma and were surrounded in part by dense fibrous connective tissue. Six cases had an incomplete rim of lamellar bone with occasional perpendicularly oriented spicules of bone. Five lesions were immunostained. S-100 protein, neuron specific enolase, and Leu-7 were found in three out of five tumours. Glial fibrillary acidic protein, smooth muscle actin (SMA), and muscle specific actin (MSA) were detected in two out of five lesions, although staining for SMA and MSA was weak in reactivity. Staining for vimentin was strongly positive in all five cases tested. The tumours were not reactive with antibodies directed against cytokeratin, epithelial membrane antigen or neurofilament protein. Follow-up information, available in eight cases, revealed multiple local recurrences in the one tumour believed to be a malignant OFT. The histogenesis of these tumours is uncertain, although the preponderance of evidence suggests a Schwann cell origin.