Development of a Monoclonal Antibody to the aP2 Protein to Identify Adipocyte Precursors in Tumours of Adipose Differentiation

aP2 gene product (aP2 protein) expression has been shown to be a useful diagnostic marker for identification of lipoblasts and fetal fat cells in soft tissue tumours. A monoclonal antibody was developed by a mouse spleen cell-myeloma hybridoma technique to an 18 amino acid segment of the aP2 protein and was used to investigate the immunohistochemical expression of this protein in benign and malignant tumours of adipocytic differentiation and a wide variety of other soft tissue tumours. We found that aP2 protein was expressed by lipoblasts in liposarcomas and lipoblastomas and by brown fat cells in hibemomas and normal periadrenal fat. Other benign adipose tissue tumours and benign and malignant soft tissue tumours were distinguished from liposarcoma by absence of staining for aP2 protein. Immunohistochemical identification of the aP2 protein is likely to prove a useful means of distinguishing liposarcoma from other malignant mesenchymal and epithelial neoplasms, some of which contain cells that morphologically resemble lipoblasts.