Lectin histochemistry of malignant fibrohistiocytic tumors

The staining pattern by Ricinus communis agglutinin (RCA), a lectin used as a good marker for histiocytes, in 24 cases with malignant fibrous histiocytoma (MFH) was studied and compared with that of 12 cases of fibrosarcoma (FS). In 20 (83%) of 24 cases of MFH, varying degrees of RCA binding were observed, whereas only four (33%) of 12 cases of FS were positive. RCA-positive FS included three cases with infantile FS and one adult case with post-radiation FS. Eight adult patients with FS were entirely negative. This positivity rate of RCA binding in MFH was much higher than those of antisera against lysozyme, alpha-1-antitrypsin, and alpha-1-antichymotrypsin previously reported. Seven MFH patients with focal aggregation of RCA-positive benign-appearing (reactive) histiocytes died earlier than the other patients with only scattered RCA-positive histiocytes; 5-year survival rates were 32% and 69%, respectively (p less than 0.05). These findings suggest that RCA reactivity can be used as a potential diagnostic and prognostic marker for MFH.