OSSIFYING FIBROMYXOID TUMOR OF SOFT PARTS - A MORPHOLOGICAL AND IMMUNOHISTOCHEMICAL STUDY

A case is presented of ossifying fibromyxoid tumor of soft parts (OFMT SP) which occurred in the left cheek of a 59 year old Chinese woman. H istologically, the tumor was located in the subcutis with a fibrous ps eudocapsule that contained discontinuous rims of mature trabecular bon e. The tumor cells were small, round to ovoid with a uniform, round nu cleus and a pale or slightly eosinophilic cytoplasm. Most of the cells were arranged in a random manner, some in a vague lace-like pattern. Mitotic figures were extremely rare. The stroma appeared fibromyxoid w ith scattered foci of mucinous lakes. Immunohistochemically, most of t he neoplastic cells displayed immunoreactivities for S-100 protein, S- 100 protein alpha, vimentin and alpha-smooth muscle actin; many tumor cells were positive for desmin. The tumor also showed stromal immunore activity for type IV collagen and was negative for cytokeratins, epith elial membrane antigen, glial fibrillary acidic protein, neurofilament s, muscle-specific actin, Leu-7, myelin-basic protein, osteocalcin and melanoma-specific antigen. The immunophenotypes expressed by the pres ent OFMTSP seem to reflect two lineages of neoplastic cell differentia tion, that is of nerve sheath and of smooth muscle; at the present sta ge, it is premature to diagnose this lesion as either nerve sheath or smooth muscle tumor.