S-100 PROTEIN STAINING IN LIPOSARCOMA - ITS DIAGNOSTIC UTILITY IN THEHIGH-GRADE MYXOID (ROUND-CELL) VARIANT

S-100 protein is a calcium-binding protein that is characterized by a wide distribution within human tissues. The distribution of immunoreac tivity using S-100 antibodies includes glial and Schwann cells, melano cytes, Langerhans' cells, chondrocytes, myoepithelial cells, interdigi tating reticulum cells, striated muscle cells, reactive mesothelium, a dipocytes, as well as many of the benign and malignant neoplasms there of. Liposarcoma is the most common sarcoma in adults. Although the dia gnostic utility of S-100 protein in this specific setting has been par tially elucidated by previous studies, its application to poorly diffe rentiated adipocytic tumors has not been specifically addressed. A ser ies of 100 cases of liposarcoma (all histologic types) was analyzed im munohistochemically using a polyclonal S-100 protein antiserum. Positi ve immunoreactivity in lipogenic or lipoblastic areas was observed in 65% of well-differentiated liposarcomas, 36% of myxoid/round cell lipo sarcomas, and 54% of pleomorphic liposarcomas. The spindle cell compon ent of myxoid tumors exhibited positive immunoreactivity in 40% of cas es, whereas round cell undifferentiated areas were positive in 50% of cases in the myxoid or round cell group. Pure round cell neoplasms sho wed positive immunoreactivity in 71% of cases. The authors conclude th at when dealing with poorly differentiated tumors, S-100 protein immun oreactivity may represent a useful diagnostic tool that permits the di fferentiation of round cell liposarcoma from other round cell malignan cies as well as the easier recognition of pleomorphic liposarcoma in s ome cases.