Increased midkine expression in hepatocellular carcinoma - Immunohistochemical and in situ hybridization analyses

Context.-Midkine (MK) is a novel heparin-binding growth factor whose gene w as identified in embryonal carcinoma cells in early stages of retinoic acid -induced differentiation. Objective.-To examine the overexpression of MK in hepatocellular carcinoma (HCC). Methods.-Seventy-seven primary HCC specimens from patients aged 17 to 72 ye ars (63 men and 14 women) were examined. Histologically, 16 cases of HCC we re classified as the well-differentiated type, 50 cases as the moderately d ifferentiated type, and 11 cases as the poorly differentiated type. Immunoh istochemical analysis was performed using a rat immunoglobulin G2a monoclon al antibody against the carboxyl terminal region of human MK. In situ hybri dization was also performed on 20 HCC samples. Results.-We successfully applied this monoclonal antibody against MK to ana lyze archival paraffin sections. The cancer tissues showed a positive react ion to this antibody, in which there was an intense reaction in their cytop lasm. Approximately one third of the individuals with HCC (26/77) had tumor tells that expressed MK, and these were classified into the following type s: moderately differentiated (20/50), well differentiated (3/16), and poorl y differentiated (3/11). The in situ hybridization analysis revealed that t he signals of MK transcripts were found in the cytoplasm of the cancer cell s; the distribution and localization of the MK transcripts' signals determi ned by in situ hybridization analysis were similar to those obtained by imm unohistochemical analysis. Conclusions.-Hepatocellular carcinoma expressed increased MK at the messeng er RNA and protein level.